Catalytic Abatement of Methane Emission from CNG …canchemtrans.ca/uploads/journals/CCT-2015-0227.pdf · etc. Various parameters used for catalytic oxidation of methane such as calcinations

Borderless Science Publishing 381

Canadian Chemical Transactions Year 2015 | Volume 3 | Issue 4 | Page 381-409

Review DOI:10.13179/canchemtrans.2015.03.04.0227

Catalytic Abatement of Methane Emission from CNG

Vehicles: An Overview

Maninder Kumar1, Gaurav Rattan1,*, and Ram Prasad2

1Dr. S. S. Bhatnagar University Institute of Chemical Engineering & Technology, Panjab University,

Chandigarh, India. 2Department of Chemical Engineering & Technology, Indian Institute of Technology (BHU), Varanasi, UP,

India.

Corresponding author: E-mail: [email protected] +91-8288071498

Received: August 27, 2015 Revised: October 28, 2015 Accepted: October 29, 2015 Published: October 30, 2015

Abstract: Compressed natural gas (CNG) is a substitution of alternative fuel for automotive application

with significant environmental advantages as it is the only fuel cheaper than gasoline or diesel,

comparatively lower air pollution emissions, lesser CO2 emissions. However, emission of methane is 40%

more in CNG fuelled engines compared to gasoline and diesel. With the exponential growth in CNG fuelled

vehicles, CH4 concentrations have reached an alarming level in the environment. It affects human health

and climate change as the Global Warming Potential (GWP) of methane is 21 times more than CO2 which

means that CH4 will cause 21 times as much warming as an equivalent mass of CO2.

Stringent regulations have been adopted to curb the menace of vehicular pollution. In order to meet

the stringent regulations Catalytic convertor using noble metals proved to a boon in vehicular industry.

Noble metals are highly active for removal of methane as a pollutant. However, their expensiveness,

deterioration with time can generate even more toxic volatile pollutants. So, researchers have tried to

substitute the noble metals with transition base metals. Further, low cost, easy availability and advance

synthesis methods of catalyst preparation advocates for the use of base metals in an auto exhaust purification

catalysts.

Ample literature has been accumulated which constitutes of review articles, research papers, PhD

thesis, proceedings etc. on methane oxidation, but still there is a gap in literature for a review article which

directs the methane oxidation with CNG exhaust emissions. Therefore in order to fill this gap present review

updates and evaluates the progress of various catalysts for purification of CNG exhaust emissions. This

paper reveals a brief discussion on CNG as an alternative fuel, various catalysts, operating parameters

reported in the literature.

Keywords: CNG exhaust emissions, Methane oxidation, Review, Catalysts, Pollution abatement.

Abbreviations: CNG: Compressed Natural Gas; NMHCs: Non-Methane Hydrocarbons; IC: Internal

Combustion; THCs: Total Hydrocarbons; GHP: Green House Potential; IPCC: Intergovernmental Panel on

mailto:[email protected]



Climate Change; EU: European Union; LPG: Liquefied Petroleum Gas; Calc. : Calcination; Temp. :

Temperature; STP: Standard Temperature & Pressure; GHSV: Gas Hourly Space Velocity; WHSV: Weight

Hourly Space Velocity; MHSV: Mass Hourly Space Velocity; ppm : Parts Per Million; mg: milligram; SV:

Space Velocity; Pepn: Preparation ; mL/min: millilitre per minute; HDP: Homogeneous Deposition

Precipitation Method; HCs: Hydrocarbons; NOx: Nitrogen Oxides; T100%= X°C: Means 100% oxidation

takes place at temperature of X°C; XRD: X-Ray Diffraction; TPR: Temperature Programmed Reduction;

XPS: X-Ray Photoelectron Spectroscopy; TGA-DSC: Thermal Gravity Analysis Differential Scanning

Calorimetry; BET: Brunauer-Emmett-Teller technique; TWC: Three Way Catalytic Convertor

1. INTRODUCTION

The combustion of conventional petroleum fuels leads to toxic emissions, global warming and

hence climate change which threatens the survival of life. Moreover with rising number of vehicles, the oil

reserves are exhausting at alarming rates. Therefore the challenge before the researchers is to investigate

alternatives for clean and efficient fuel. Natural gas provides an attractive fuel since it is available in

abundant supply. It is produced from gas wells or tied in with crude oil production. Natural gas has many

constituent gases such as methane, ethane, propane, nitrogen, helium, carbon dioxide, hydrogen sulphide,

and water vapour. Composition of these gases depends on the source of its origin. Composition of natural

gas is shown in table 1.

Table 1. Natural gas composition [1]

Composition Volume Fraction (%)

Methane(CH4) 94.00 92.07 94.39 91.82

Ethane(C2H6) 3.30 4.66 3.29 2.91

Propane(C3H8) 1.00 1.13 0.57 -

Iso-Butane(i-C4H10) 0.15 0.21 0.11 -

n-Butane(n-C4H10) 0.20 0.29 0.15 -

Iso-Pentane(i-C5H12) 0.02 0.10 0.05 -

n-Pentane(n-C5H12) 0.02 0.08 0.06 -

Nitrogen(N2) 1.00 1.02 0.96 4.46

Carbon Dioxide(CO2) 0.30 0.26 0.28 0.81

Hexane(C6+ (C6H14)) 0.01 0.17 0.13 -

Oxygen(O2) - 0.01 <0.01 -

Carbon

Monoxide(CO)

- <0.01 <0.01 -

Total 100 100 100

Natural gas can be easily compressed, so it can be stored and used as compressed natural gas

(CNG). CNG is colourless, odourless, non-toxic, lighter than air and inflammable. There are over 1,500,000

vehicles in the world produced by Honda, Ford, Toyota, Volvo, Mercedes Benz, Optare and Scania running

on CNG [2]. CNG engines guarantee considerable advantages over conventional gasoline and diesel

engines [3]. CNG is attractive for many reasons such as it is the only fuel cheaper than gasoline or diesel,

has comparatively lower air pollution emissions, lesser greenhouse gas emissions, large quantities of the

fuel is available. Being a gaseous-fuel it does not require cold-start enrichment; emissions from "cold"



engine operation are higher than with liquid fuels [4]. As it is non-toxic gas and it will not contaminate

groundwater if spilled in comparison to gasoline and diesel. The CNG fuel properties are shown in Table

2.

Table 2. CNG fuel properties at 250C and 1 atm [24]

CNG Properties Value

Density (kg/m3) 0.72 0.68

Flammability limits (volume % in air) 4.3-15 4-14

Flammability limits (Ø) 0.4-1.6 -

Autoignition temperature in air (0C) 723 700

Minimum ignition energy (mJ) 0.28 -

Flame velocity (ms-1) 0.38 0.63

Adiabatic flame temperature (K) 2214 -

Quenching distance (mm) 2.1 -

Stoichiometric fuel/air mass ratio 0.069 0.058

Stoichiometric volume fraction % 9.48 -

Lower heating value (MJ/kg) 45.8 -

Heat of combustion (MJ/kgair) 2.9 -

Octane rating - 130

Advantages of CNG according to Jahirul et al. [5] are as follows:

Unique combustion and suitable mixture formation;

Due to high octane number, engine operates smoothly with high compression ratios without

knocking;

During lean burning conditions it will lead to low exhaust emissions and fuel operating cost;

It has a lower flame speed;

Engine durability is very high.

The formation of non-methane hydrocarbons and other air pollutants in CNG fuelled engines are one-

tenth than those of gasoline engines [6]. The formation of CO and NOx are 80% lower than gasoline engines

because of simple chemical structures of natural gas (primarily methane (CH4)) contain single Carbon

compare to diesel (C15H32) and gasoline (C8H18). In terms of economy CNG fuelled engines are 20% more

economical than gasoline and diesel engines.

However, some difficulties with CNG fuelled vehicles are: a) Fuel storage, b) Infrastructure costs, and

c) Ensuring sufficient supply. As CNG requires a much larger volume to store the same mass of natural gas

and a very high pressure of about 200 bars or 2,900 psi [4] which requires the additional chambers, storage

cylinders which in turn increases weight of the vehicle. With exponential rise in the CNG fuelled vehicles

would require new gas pipelines, CNG specific fuel stations and other infrastructure. Due to on-board

storage, the engine knocks at high loads [7]. CNG advantages are partially balanced by the emission of

unburned methane. The hydrocarbon composition in the exhaust gases of lean-burn CNG engines reflects

the composition of natural gas in methane and non-methanic hydrocarbons (NMHCs), typically 90–95%

methane [8]. The typical composition of CNG is given in Table 3.



Table 3. Typical Composition (Vol %) of Compressed Natural gas [2]

Component Volumetric %

Methane (CH4) 94.42

Ethane (C2H6) 2.29

Propane (C3H8) 0.03

Butane (C4H10) 0.25

Nitrogen (N2) 0.44

Carbon dioxide (CO2) 0.57

Others 2

Methane is a potent greenhouse gas and its global warming potential is about 21 times than CO2

[9]. It contributes more to global atmosphere warming than carbon dioxide at equivalent emission rates. It

leads to climatic change which is due to the presence of such greenhouse gases. Methane has the most stable

structure compared to other hydrocarbons and is more difficult to be oxidized than most HCs. The catalytic

oxidation of methane is an easy way of automobile emission control as shown by the equation (1).

CH4 [g] + 2O2 [g] → CO2 [g] + 2H2O [g] + heat (890 kJ/mol)……. (1)

The catalytic conversion of CH4 to CO2 and H2O helps in reducing global warming. Further CO2

and H2O found in the atmosphere are useful for vegetation. CH4 oxidation has been studied broadly over

various types of catalysts such as gold based catalyst [9-10] noble metals (Pt, Pd, Rh, Au, etc.) [11-12], base

metals [13-14], mixture of noble and base metals [15], perovskites [16-18] etc. Various review articles has

been published [8, 19], number of PhD [20-21] has been awarded by various universities on the CNG

exhaust emissions and control. Also various controlling techniques and methods, catalysts have been

depicted in many patents [22-23] but still there is a gap in literature for a review article which relates the

methane emissions from CNG vehicles with the various catalysts for its abatement and control.

Therefore this paper aims to summarize the latest research results regarding the catalysts used for

methane oxidation. Complete analyses have been made of CNG properties, its advantages, disadvantages,

etc. Various parameters used for catalytic oxidation of methane such as calcinations temperature, flow rate,

other experimental operating parameters are presented in a tabular form. The sources and effect of CH4 on

humans, environment and ways to minimize emissions have also been discussed.

2. SOURCES OF METHANE EMISSIONS

Methane is colourless, odourless; tetrahedron structure (figure 2) gas having boiling point of 111.66

K. It is lighter than air which makes it very easily escapable gas from wherever it is stored or processed.

Hydrogen sulphide (which smells like rotten egg) is usually mixed with methane by the commercial energy

companies for the detection of its leakage. CH4 is a “greenhouse gas,” meaning that it traps infrared

radiation (heat) from the earth’s surface and increases the temperature of the earth. During the past century,

humans have substantially added to the amount of greenhouse gases in the atmosphere through activities

such as burning fossil fuels and deforestation. According to a study CNG fuelled transit buses have higher

methane emissions than diesels [25]. CNG engine emission results are shown in figure 1 [25].

CH4 is emitted from both natural and anthropogenic sources. Large portion of the gas is emitted

from the industrial sector such as petrochemicals [27-28]. It is generally emitted to the atmosphere during



the production, processing, storage and distribution which accounts for the huge amount to the atmosphere.

Apart from industries methane is also emitted from the flora and fauna which adds great amount of methane

as pollutant to the atmosphere. Methane is also emitted from wetland rice fields [29-30], terrestrial plants

under aerobic conditions [31], cattle [32], landfills and biomass burning.

Figure 2. Structure of Methane

2.1. CH4 from Internal Combustion Engine

CH4 is emitted from gasoline, diesel, methanol, ethanol, LPG, and natural gas internal-combustion-

engine vehicles. These emissions occur due to incomplete or partial fuel combustion, which produces CH4,

CO, PM along with other unburned hydrocarbons. This usually occurs when the ratio of air to fuel in

combustion chamber is too low for complete combustion i.e. there is inadequate oxygen to convert all CH4

present in the fuel to CO2 and H2O and heat. When internal combustion engine gets a stoichiometric mixture

of air and fuel, 17.2 parts by weight of air and one part by weight of CNG (almost methane), it emits

minimum amount of pollutants. But the combustion process is never found to be 100% efficient in IC engine

(Equation-1). Hence, under ideal conditions only the engine operates efficiently and would generate CO2,

H2O and heat. However, emissions depends upon so many factors [33], such as (i) Type of fuel used, (ii)

The design of engine, (iii) Tuning of the engine, (iv) Type of emission control system, (v) Age of the vehicle.

Figure 1 shows the comparison of exhaust gases of CNG and gasoline fuelled engines.

Figure 1. Comparison of exhaust gases of CNG and gasoline fuelled engines [25]

[g/km]

CNG

Gasoline



Moreover, CH4 has the most stable structure compared to other organic gases and is difficult to

oxidise catalytically, the systems used to control emissions of NMHCs and total hydrocarbons (THCs) do

not have the same effectiveness in controlling CH4 emissions as they do in controlling NMHCs. According

to a report, CH4 emissions from vehicles with hydrocarbon controls might be about 3 times less than CH4

emissions from vehicles with no controls. Methane from Internal-combustion-engine vehicles using fossil

fuels is presented in table 4. Vehicles without a catalytic converter emit 0.3 g/mile CH4 in comparison with

0.1 g/mile CH4 for vehicles provided with a catalytic converter. As expected that vehicles using natural gas

would emit considerably more CH4 than gasoline engines. CH4 emissions from natural gas vehicles (NGVs)

range from 0.6 to 4 g/mile for dual-fuel vehicles (which carry and use two fuels, gasoline and natural gas),

and between 0.13 and 3 g/mile for dedicated vehicles (which carry and use only natural gas) [33]. During

cold start period, gasoline engines emit much higher amount of hydrocarbons compared with the natural

gas [27]. This is mainly because CH4 is a gas at all ambient temperature and hence does not have to be

vaporized as in the case of gasoline, temperature-dependent process. Content of methane emission by

various tests is shown in table 5.

Table 4. The percentage contribution of individual GHGs to lifecycle CO2-equivalent emissions for

alternative transportation fuels for light-duty vehicles [33]

Fuel→

Conventional

gasoline

Reformulated

gasoline

Low

sulphur

diesel

85%

methanol

Compressed

natural gas

Compressed

hydrogen

LPG

CH4 3% 3% 3% 5% 17% 7% 4%

Table 5. Content of methane emission [33]

CH4 content of natural gas 86% 90% 94% 97%

CH4 emissions from vehicles in grams per mile

(REP05 cycle/FTP cycle)

0.47/0.91 0.50/0.93 0.48/0.96 0.49/0.92

FTP: Federal Test Procedure, REP05: the EPA’s high-speed, high-load driving cycle used

2.2. Adverse effect of methane

Methane emissions adversely affect humans and environment. It has drastic effects on nature as GHP and

hence climate change.

2.2.1. Effects on humans

In normal circumstances, methane is not toxic to humans. It causes asphyxiation by displacing oxygen.

However long-term exposure of methane to humans can cause loss of consciousness, depression,

suffocation, emotional upset, fatigue, nausea or even death can occur.



2.2.2. Effects on nature

The presence of methane in the atmosphere has been known since the 1940’s when Migeotte [34]

observed strong absorption bands in the infra-red region of the solar spectrum which were attributed to the

presence of atmospheric methane. Methane has a much greater impact on global warming than carbon

dioxide and it is the most damaging greenhouse gas produced by human activity after carbon dioxide [26].

According to IPCC 2013 [74], the surface mixing ratio of CH4 has increased by 150% since pre-industrial

times with some projections indicating a further doubling by 2100. A recent report by IPCC 2014 [92]

shows the trends of temperature increase from the past time. Climatic changes due to greenhouse effect are

likely to have an effect on water sources and supplies and the increase in temperature will induce a new

distribution of deserts and wet areas in the world.

Methane is also the most abundant reactive trace gas in the troposphere and its reactivity is

important to both tropospheric and stratospheric chemistry. The oxidation of CH4 by hydroxyl (OH) in the

troposphere leads to the formation of formaldehyde (CH2O), carbon monoxide (CO), and ozone (O3), in the

presence of sufficiently high levels of nitrogen oxides (NOx). Along with CO, methane helps control the

amount of OH in the troposphere. Methane affects the concentrations of water vapour and ozone in the

stratosphere, and plays a key role in the conversion of reactive chlorine to less reactive HCl in the

stratosphere [35]

2.2.3. Formaldehyde emission

Compared to low-emitting diesel, the CNG exhaust had higher levels of six toxic air contaminants

(TAC) listed by the California Air Resources Board (ARB)—acetaldehyde, acrolein, benzene,

formaldehyde, methyl ethyl ketone, and propionaldehyde—and did not have lower emissions of any TAC.

Formaldehyde emission is very high with CNG vehicles. Formaldehyde is classified as a toxic air

contaminant and is known carcinogenic. Inhalation of high doses of formaldehyde has produced nasal

tumors in laboratory rats, and lower concentrations have irritated eyes and air passages in humans.

Thresholds for sensory irritation determined by controlled exposure studies, are reported as 0.6-1.2 mg/m3

[0.5-1.0 ppm] (formaldehyde); 0.1-0.2 mg/m3 [0.04-0.09 ppm] (acrolein); and 90 mg/m3 [50 ppm]

(acetaldehyde) [70].

3. EMISSION REGULATIONS

With exponential growth of vehicles on roads, CH4 concentration has reached an alarming level in

the environment. According to the IPCC 2014 [92] “With high levels of warming that result from continued

growth in GHG emissions, risks will be challenging to manage, and even serious, sustained investments in

adaptation will face limits”. In order to manage harmful exhaust emissions stringent regulations have been

adopted from time to time. Environmental protection agency (EPA) setup in 1970 in order to reduce

automobile pollution and is still in development process. In October, 2003, the National Auto Fuel Policy

was announced, in which Indian automobile emissions are revised according to European Union,

introducing Euro 2–4 emission as Bharat Stage (BS II-IV) and fuel regulations by 2010 [36]. The

implementation schedule of EU emission standards in India is summarized in Table 6. For detail description

of various emissions norms read [37].



Table 6. Emission norms in India parallel to EU emission standards

NORMS Year CO (g/Km) HC + NOx (g/Km)

1991Norms - - 14.3-27.1 2.0(Only HC)

1996 Norms - - 8.68-12.40 3.00-4.36

1998Norms - - 4.34-6.20 1.50-2.18

India stage 2000 norms Euro 1 2000 2.72 0.97

Bharat stage-II Euro 2 2001 2.2 0.5

Bharat Stage-III Euro 3 2005 2.3 0.35(combined)

Bharat Stage-IV Euro 4 2010 1.0 0.18(combined)

Bharat Stage-V Euro 5 2011

However the emission standards for CNG fuelled vehicles runs parallel to gasoline and diesel fuelled

engines with certain modifications. Mass emission standards for CNG fuelled vehicles are same as

applicable for gasoline vehicles with an exception that HC shall be replaced by NMHC, where NMHC=

0.3 x HC [37]. Table 7 represents a brief detail of CNG emission standards.

Table 7. CNG EMISSION STANDARDS [37]

Category Applicable emission norms

OE CNG/ LPG Category M and Category N Vehicles

with GVW 3500kg, 3 wheelers and 2 wheelers

Prevailing gasoline norms *

CNG/LPG Category M and Category N Vehicles with

GVW 3500kg, 3 wheelers and 2 wheelers retro fitment

from Gasoline

Prevailing gasoline norms


GVW 3500kg, 3 wheelers and 2 wheelers retro fitment

from Diesel

Prevailing diesel norms**


GVW > 3500kg, manufactured upto 1st April 2010

Prevailing diesel engine norms based on 13-

mode steady-state engine dynamometer test

or 13 -mode Engine steady state cycle as

applicable **


GVW > 3500kg, manufactured on and from 1st April

2010

Prevailing diesel engine norms **

*-Vehicle having option for bi-fuel operation and fitted with limp-home gasoline tank of capacity not

exceeding 2 liters, 3 liters and 5 liters respectively on 2W, 3W and 4W are exempted from emission test,

crankcase emission test and SHED test in gasoline mode.

**-PM limit is not applicable

It is important to note that although methane emissions not regulated in the above given table.

Regulations are adopted for hydrocarbon and Non-Methane hydrocarbons where as methane is not

regulated. Methane is also not regulated in many parts of the developing countries, USA etc.



4. ACTIONS TO REDUCE CH4 EMISSIONS

It is likely that the emission legislation will be more stringent in the near future, since the current

limits lead to unacceptable emissions from a health point of view [38]. As emissions are a result of many

parameters and these parameters can be optimised in order to reduce or meet the stringent legislations.

There are two principal approaches for decreasing CH4 emission from internal combustion engines.

1. Optimisation of the combustion process, fuel modification or fuel additives, modification to motor

engines.

2. Cleaning of exhaust gases: catalytic oxidation using catalytic convertor.

The present review is primarily concerned with catalytic convertor used in exhaust of vehicles, hence

emphasis is on various catalysts used in the catalytic convertor.

4.1. Catalytic Converter

Frenchman Eugene Houdry a mechanical engineer and expert in catalytic oil refining invented the

catalytic converter in 1950s. Catalytic convertor was introduced in USA in 1974 [39] and in European

vehicles in 1985. Catalytic converter is fitted before the vehicular exhaust in order to reduce harmful

pollutants such as unburned Hydrocarbon (HCs), Carbon monoxide (CO) and Oxides of nitrogen (NOx)

into less harmful components. A three-way catalytic converter has three simultaneous tasks: reduction of

NOx [equation-(2)], Oxidation of CO [equation- (3)] and unburned HCs [equation- (4)].

2NOx → xO2 + N2 (2)

2CO + O2 → 2CO2 (3)

CXH2X+2 + [(3x + 1)/2]O2 → xCO2 + (x+1)H2O (4)

The three noble metals that are used in Catalytic converter are platinum, palladium and rhodium

[40]. Catalytic converter consists of two ceramic blocks with micro ducts which are used in order to increase

the contact zone between gases and catalyst. The increase in surface area is greater than the area of soccer

field. The ducts consist of platinum and rhodium in one block while platinum and palladium in the other

block, acting as catalysts. As the gas enters inside the catalyst the above reactions (equations 2-4) take

place.

When the automobile starts, both the engine and catalyst are cold. After some time, the heat of combustion

is transferred from the engine and the exhaust piping begins to heat up. Finally, a temperature is reached

within the catalyst that initiates the catalytic reactions. This light-off temperature and the concurrent

reaction rate is kinetically controlled; i.e., it depends on the chemistry of the catalyst since the transport

reactions are fast. Typically, the CO reaction begins first followed by the HC and NOx reaction [41]. There

is decrease in activity of the catalyst with time. One would expect that pollutants including CH4 to increase

somewhat as the engine and the emission-control system age and deteriorate or deterioration of catalytic

convertor. The data do suggest that for most petroleum fuels as well as nonpetroleum fuels, CH4 emissions

increase with the age of the catalyst [33].

Various factors are responsible for the deactivation of the catalyst such as 1) Deposited poisons that

cover the active sites of the catalyst and partially plug the pore entrance. 2) Chemisorbed poison which is



a result of the compounds that are present in the reactant gasses such as sulphur which chemisorbed on the

catalyst surface. The three way catalytic convertor has same problem of poisoning. 3) Diffusion poisons

that results due to the blocking of the pore mouths of the catalyst and prevents the reactant from diffusing

into the inner surface of the catalyst.

5. CATALYSTS FOR CH4 COMBUSTION/OXIDATION

5.1. Gold-Based Catalysts

Gold is the least reactive metal and it has been regarded as poorly active as a heterogeneous catalyst

[42]. However, it was only since the discovery of gold nano particles that gold has been getting considerable

interest in the field of catalysis. Since then number of patents [43-44], PhD degree [20] and various articles

has been published [15, 45-46]. Early work of Haruta et al. on catalysis showed that Au catalysts are very

active for CO oxidation even at sub-ambient temperatures [47]. Also the application of supported gold

catalysts for the total oxidation of methane has been addressed in earlier studies [9, 42, 46, 48]. Waters and

his colleagues made a considerable effort on methane combustion over transition metal oxide supported

gold catalysts prepared by co-precipitation, and concluded that the best catalytic performance was obtained

with Co3O4 as the support [45].

Various supports were tested for methane oxidation that was active for methane combustion in the

absence of gold at higher temperatures. Au/CoOx prepared by co-precipitation method can oxidise 100%

CH4 at temperature of 350°C [49] and it was concluded that the catalytic activity of Au/Co3O4 (Au loading

was 2–5 wt. %) towards methane combustion could be enhanced with addition of small amount of Pt, e.g.

0.2 wt. %, and the temperature for 100% conversion of methane could be decreased by 50 °C. Liotta studied

the effect of cerium addition on AuCo catalyst. The CeO2 in AuCoCe plays the role of a structural promoter,

limiting the Au sintering and the Co3O4 decomposition at temperature above > 600°C [15]. Moreover, the

activity of Au/Al2O3 and Au/MOx/Al2O3 (M = Cr, Mn, Fe, Co, Ni, Cu and Zn) catalysts for oxidation of

CH4 has also been studied [10].

Table 8. Recent literature review at glance of methane combustion on gold based catalysts.

Catalyst, Pepn. Method

Exp Operating Parameters Remark Reference

Au/TiO2, Au/SiO2, Au/CeO2,

Au/ZrO2, Au/Al2O3,

Deposition Precipitation, Calc.

temp. 400 °C

Quartz tubular fixed bed, 50

mL/min. (20% CH4 and 5% O2

rest is He.

Au/TiO2 shows T80%=

400°C, where as

Au/Al2O3 shows

T20%=400°C.

[46]

Co3O4/CeO2 and Co3O4/CeO2–

ZrO2

Co-precipitation, Calc. temp.

650 °C

quartz U-shaped,

0.3 vol.% of CH4 + 4.8 or 0.6

vol.% O2 , in He. 50 mL/min

(STP),

WHSV of 12000 or 60000

mL/g h.

Co3O4/CeO2 shows

T100%= 800°C

[14]

Au/CoOx, Au/MnOx co-

precipitation,

Calc. temp. 400 °C

50 mg, fixed-bed

S. S. tubular flow, 50 mL/min.,

GHSV = 15,000 h-1, alkane/air

Au/CoOx

Shows T100%= 350 °C.

[48]



( molar ratio) of 0.5/99.5

Au/Co3O4–CeO2

co-precipitation,

Calc. temp. 600 °C.

50 mg, U-shaped quartz,

0.3 vol.%CH4, 2.4 vol.%O2 in

He.

WHSV=60,000 mL/ gh.

AuCeO2 shows

T100%=750°C.

[15]

Au/MgO,

Impregnation,


200 mg, microreactor of quartz

glass, CH4 (46%, O2 8%, He

46%. GHSV=750 h-1.

Enhanced activity when

gold was employed

[51]

Au–Pt/Co3O4

coprecipitation technique


0.10 g, fixed bed microreactor,

1 vol.% CH4,

5 vol.% O2, and rest N2., hourly

space velocity of 10,000 per

hour

Activity of Au/Co3O4

enhanced when Pt, e.g.

0.2 wt.% was added,

and conv. Temp.

decreased by 50°C.

[49]

Au/MOx/Al2O3

where M is Cr, Mn, Fe, Co, Ni,

Cu, and Zn, homogeneous

deposition precipitation, Calc.

temp. 400 °C

lab-scale fixed-bed, 0.8 vol.%

CH4 and 3.2 vol.% O2 in He, 30

mL/min.

Au/MnOx/Al2O3 shows

T100%= 25°C for CO.

whereas MnOx/Al2O3

shows T80%= 375°C

[10]

CoxMny

co-precipitation,

Calc. temp. 400 °C

0.5 g, fixed-bed quartz,

1 vol.% CH4, 10 vol.% O2 and

N2 balance gas, flow rate =150

mL/min, WHSV= 36,000

mL/hg.

Co5Mn exhibits good

result with T50%=290°C

T90%=320°C

T100%=400°C

[52]

Au/Fe2O3

Deposition precipitation,

0.1 g, fixed bed quartz,

1 vol.% CH4 in air, flow

rate=100 mL/min, GHSV =

51,000 h-1.

Au/Fe2O3 prep. By HDP

shows T50%=375°C,

T100%=500°C.

[9]

AuOx/Ce0.6Zr0.3Y0.1O2

Co-precipitation,

Calc. temp. 700 °C

0.12 mL, quartz fixed-bed

microreactor,

5% CH4/95% He (v/v, 40

mL/min) + O2 (8 mL/min) + He

(52 mL/min),

SV= 50,000 h-1.

Catalyst with 6% AuOx

shows T50%=590°C

T100%=680°C

[53]

AgMnLa,

Coprecipitation,

Calc. temp. of 800 °C

0.15 g,

2 vol% CH4 in air,

300 cm3/min,

SV=120,000 cm3/(h gcat),

Catalyst with 0.3 %

mole fraction of Ag

shows T50%=600°C and

T100%=700°C

[54]

A higher methane conversion was observed for catalysts with small gold particles. However work

reported by Chaudhary and his colleagues [9] on gold based catalysts showed that Au/Fe2O3 prepared by

HDP method is the best catalyst for CH4 oxidation among various other metal oxide (viz. MnO2, CoOx,



CeO2, Ga2O3, Al2O3, TiO2 and MgO) supported gold catalysts. Apart from the oxidation studies, various

routes have also been suggested for preparation of gold based catalysts. Ivanova reported the preparation

Table 9. Parameters of some publication related to noble metal based catalysts


exp operating parameters REMARK Ref

monolith catalysts of

5 wt% Pd//Al2O3; 1:1 molar ratio of

Pd:Co, Rh, Ir, Ni, Pt, Cu, Ag,

Au,//Al2O3;

Ni//Al2O3; 2.5 wt% Pd//Al2O3;

Pt//Al2O3

Co-impregnation, Calc. temp. of 1000

°C

1.5 vol% CH4 in air

SV=250000 h-1.

5 wt% Pd//Al2O3 shows

good results with

T50%=600°C and

T90%=850°C

[62]

Pd/SnO2, Impregnation method,

Calc. temp. of 600-1000 °C

CH4 (1 vol.%), O2 (20

vol.%), H2O (0–20

vol.%), and N2, SV=

48000 h-1, quartz tube

1 wt.% Pd/SnO2 shows

T50%=350°C,

T100%=450°C

[63]

Pd/ZrO2,wet impregnation,

Calc. temp. of 600 °C

50 mg,

alumina tubular reactor,

CH4=1%, O2=4%,

He=95%.

Effect of water vapour

studied, Shows

T50%=650°C ,T90%=800°C

[64]

Pd/Al2O3, Pd/SiO2, Pd/Al2O3-SiO2

Impregnation, Calc. temp. 500 °C

0.01g, Pyrex glass,

100 mL/min of gas

mixture of 10%CH4,

20% O2, 70%N2.

The stabilized, activity of

the palladium follows

SiO2> A1203> SiO2-

A12O3.

[65]

Ce0:67Zr0:33O2, Pt/Ce0:67Zr0:33O2,

Pd/Ce0:67Zr0:33O2, Precipitation,


0.50 g catalyst, 1

vol% CH4, 4 vol%

O2, and N2, flow

rate=6.4 L/h.

Activity varies

Pd/Ce0:67Zr0:33O2 >

Pt/Ce0:67Zr0:33O2 >

Ce0:67Zr0:33O2, where

Pd/Ce0:67Zr0:33O2 shows

T50%=300 ,T100%=550°C

[11]

Pd/SiO2, sol-gel, Calc. temp. 500 °C.

200mg, 1 vol% CH4, 2

vol% O2, balance He.

Pd/SiO2 shows T50%=650,

T100%=800°C

[66]

Pd/Co3O4, Impregnation, Calc. temp.

280 °C

horizontal quartz tubular,

1.2% CH4, 12% O2,

balance N2, flow rate= 33

ml/min.

10 wt.% Pd/Co3O4

exhibits T50%=250°C,

T100%=300°C

[67]

Pd/[SO42-ZrO2, MgO, SiO2-ZrO2, SiO2,

SiO2-Al2O3, ZrO2], impregnation,

Calc. temp. 500 °C

100 mg, conventional

flow, (CH4 + O2 + He),

flow rate= 200 cm3/ min.

Pd/SiO2 shows

T50%=625°C, T90%=850°C

[68]

of gold catalysts supported on alumina by direct anionic exchange which showed a better activity than the

catalysts prepared by deposition-precipitation in the CO oxidation reaction. However gold catalysts are not



favaurable where high temperature of around 1000°C are employed because of low melting point of gold

at 1064°C. Whereas the Au/TiO2 shows a conversion of 100% at temperature of 600°C [50]. Table 8 shows

some of the developments on gold based catalysts.

5.2. Noble Metal Catalysts

Noble metal catalysts are highly active for methane combustion when supported on suitable

support. Thermal stability at high temperature makes it a favourable candidate when high temperature

conditions are employed or when there is deterioration of active sites of catalysts at high temperature [12,

55-56]. The deposition of noble metals on the support such as Al2O3, TiO2, MgO, ZrO2, La2O3 etc. which

are generally cheap compounds having very high surface area per unit mass of the catalyst reduces the

amount of the precious metal with enhanced activity. Noble metals like Pt, Pd and Rh have been extensively

studied with supports like ceria, zirconia, alumina, titania, etc. for methane oxidation [11]. Supported

palladium catalysts have been extensively studied for the catalytic combustion of methane as palladium is

more active for methane combustion than other noble metals [57]. Alumina has been widely used as a

support for the palladium catalyst due to its high specific surface area and low cost. The Pd/Al2O3 catalyst

is active at medium temperatures above 400°C, though its activity is insufficient for the low temperature

ignition, e.g. at 300°C.

The catalytic performance of PdO catalysts supported on various metal oxides (MOx; M = Al, Ga,

In, Nb, Si, Sn, Ti, Y, Zr, Ni) was studied, out of which highest activity was achieved on the most dispersed

catalysts, i.e. Pd/Al2O3–NiO and Pd/SnO2 [57]. Catalytic convertor mainly uses palladium for treatment of

the exhausts, therefore considerable work has been done on palladium in order to increase its activity. Ceria

is a well-known promoter in automotive catalysts due to its enhanced oxygen storage capacity (OSC) [58].

In particular, ceria-supported 2 wt% Palladium catalyst prepared by a deposition–precipitation method was

reported [59] to be highly active for total methane oxidation at low temperature of 300°C. Moreover effect

of ceria on palladium was studied by many authors [11, 60-61] in order to increase the activity i.e.

attainment of 100% conversion of CH4 at low temperature. But none has revealed temperature below 300°C.

However the light off temperature was revealed a bit low at 150°C [11]. Table 9 reveals some of the

development in catalyst on noble metals.

5.3. Base metal catalysts

Because of the expensiveness and non-availability of noble metals, transition metal (Ni, Cu, Mn,

Co, Fe, Cr, etc.) oxides have been considered as practical alternative materials to prepare the catalysts for

the combustion of lean methane [69, 52]. The series of base metals have been supported on different

supports in order to attain the activity as high as that of noble metals in order to decrease the high cost of

noble/gold based catalysts. The combustion/oxidation of CH4 has been explored since 1960 [71]. Since

then many advances have been made primarily for methane combustion. Recently low temperature

oxidation of methane has been reported [72-73] by the oxides of base metals. A series of MnOx(m)–NiO

composite oxide catalysts were prepared by co-precipitation method. Compared with the corresponding

single NiO and MnOx oxides, the MnOx(m)–NiO composite oxide exhibits much higher catalytic activity

in the combustion of lean methane at low temperature. The activity of MnOx(m)–NiO catalysts is related

to the content of manganese in MnOx(m)–NiO. MnOx(0.13)–NiO with an atomic ratio of n(Mn)/(n(Mn) +

n(Ni)) being 0.13 performs the best in the lean methane combustion. Methane conversion over

MnOx(0.13)–NiO reaches 96% at 396°C and 100% at 450°C, which is outstanding for a non-noble catalyst

compared with those reported in the literature.



Transition metal has been reported recently with the mixture of noble metals which is as good as

that of noble metal catalyst. Cobalt has been reported many times and still in the development process [22,

Table 10. Base metal catalysts used for methane oxidation


Exp Operating

Parameters

Remark Ref

Cu, Mn-BaAl12O19, Sol-

gel,

Calc. temp. 1200 °C

0.50 g, Quartz

microreactor,

1 vol.% CH4, 4 vol.%

O2 and 95 vol.% N2 ,

SV= 20000–25000 h-

1.

Cu sites are intrinsically more active than

Mn sites, BaMn3 shows T50%=600,

T100%=800, Where BaCu shows T50%=700,

T100%=800

[78]

Co-Mg/Al, prepared by

calc. of CoxMg3−x/Al

hydrotalcites,

precipitation at 800 °C.

0.5 g, a mixture of 1%

vol of CH4 in air, total

flow rate of 400

mL/min,

GHSV= 50,000 h-1.

catalysts with molar ratio of 1.5 of Co/Al,

shows T50%=540 °C, T100%=800 °C.

[79]

MnOx–CeO2,

Coprecipitation, 500 °C,

Plasma, Modified

coprecipitation.

150 mg, fixed-bed

reactor, 20% CH4 and

40% O2 in Ar, and

SV=40,000 mL/g h.

Ppep. T50%(°C) T80%

(°C)

T100%

(°C)

MP 350 360 480

CP 410 480 NA

PP 380 410 NA

[80]

oxides of

cobalt/manganese,

sol–gel, Calc. temp. 850

°C

0.1 g, quartz tubular

reactor, flow rate of

100 mL/min, CH4 (0.5

vol.%), O2 (0–8

vol.%), water vapor

(5 vol.%) and argon.

CoOx shows good results with T50%=425

°C and

T100%=550 °C.

[77]

CuO/AI2O3,

Wet impregnation,

Calc. temp. 500 °C

500 mg, quartz micro

reactor, 1 % CH4, 4%

02, and 95% N2, flow

rate 6.41 h-1

4.8% CuO

shows T50%=450 °C, T100%=570 °C

[82]

CeO2,

ZrO2,HfO2,Ce0.8Zr0.2O2,

and Ce0.8Hf0.2O2,

Precipitation,

coprecipitation, calc.

temp. 920 °C

quartz mic roreactor,

CH4 (l%), O2(4%) and

He, SV=34000 h-1.

Ce0.8Zr0.2O2 shows

T50%=520 °C, T100%=670 °C

[83]

Co/MgO, Wet

impregnation, Calc.

temp. 800 °C.

0.05 g, quartz reactor,

2% CH4, 8% O2 and

N2, SV=480,000 h-1.

Cobalt exhibit good activity when MgO

employed

[84]



MnOx–NiO, co-

precipitation, Calc. temp.

500 °C.

200 mg, quartz tubular

flow micro reactor,

1.0 vol.% CH4, 19

vol.% O2, and

balanced argon,

WHSV= 32 000 mL/g

h.

MnOx(0.13)–NiO exhibits

T50%=360 °C and

T100%=525 °C.

[72]

CoCr2O4, co-

precipitation , Calc.

temp. 700 °C.

250 mg, 2000 ppm

CH4, 10 vol.% O2, and

N2, GHSV= 36000

mL/h g.

Catalyst containg 5% Ce, shows T50%=375

°C and

T100%=525 °C.

[76]

CoxCry, Coprecipitation,


500 mg, 2000 ppm

CH4, 10 vol.% O2, 10

vol.% and N2, flow

rate= 300 mL/min,

GHSV= 36000 mL/h

g.

Co/Cr=0.5 shows, T50%=400 °C and

T100%=550 °C.

[73]

Co3O4/CeO2 and

Co3O4/CeO2–ZrO2, co-

precipitation,

impregnation, Calc.

temp. 750 °C.

0.3% of CH4 + 4.8%

of O2 in He,

WHSV= 12,000 mL/

g h,

SV= 60000 mL/ g h

Catalyst with 30% Co3O4 shows

T50%=400 °C, T100%=700 °C

[13]

Cerium-chromium/γ-

Al2O3

incipient

wetness impregnation,

Calc. temp. 500, 800 °C.

300 mg, stainless-

steel fixed bed, 2.0

vol.% CH4,

8 vol.% O2, 90 vol. %

N2, MHSV= 20,000

mL/g h.

3 wt.% Ce displayed T50%=375°C,

T100%=475 °C

[85]

CeO2-ZrO2, urea

hydrolysis,

Calc. temp. 500-900 °C.

100 mg, differential

quartz tube

microreactor, 2.0

vol.% CH4,

21 vol.% O2 and He,

flow rate= 100

mL/min.

Ce0.75Zr0.25O2 calcined at 500 °C shows

good activity with T50%=550 °C,

T100%=650 °C

[86]

CeO2-ZrO2,

Precipitation, Calc. temp.

700 °C.

500 mg, Microreactor,

1 vol.% CH4, 4 vol.%

O2 diluted in N2, Flow

rate=6.4 l h-1,

GHSV=20 000 h-1.

CeO2 shows T50%=575 °C, T100%=750 °C [87]



CuO/ZrO2, Wet

impregnation,

Calc. temp. 600 °C

200 mg, continuous

flow fixed-bed, 20

vol.% CH4, 40 vol.%

O2, 40 Ar.

ZrO2- 5% CuO shows

T50%=400 °C

T90%=425 °C

[88]

75]. From the past literature it could be concluded that complete combustion of CH4 can be attained at

temperature of around 650°C [11, 73, 76-77]. However the conversion temperature can be decreased by

varying the composition, preparation method, doping of other metals etc [76]. The minimum temperature

reported for 100% conversion of methane is 450°C by [72] using MnOx(0.13)–NiO, where 0.13 represents

the atomic ratio of [Mn]/[Mn + Ni]. i.e. the content of Mn in composite oxide. Various other parameters

such as addition of water vapour, SO2 [73] have also been studied. Manganese oxide has been reported for

the lean oxidation of methane at low temperature [72]. The author has given a brief explanation about the

structure and various properties using the advanced techniques of characterisation such as XRD, XPS,

TEM, HRTEM, XAS, and FTIR. It was demonstrated that activity varies as MnOx(0.13)–NiO >

MnOx(0.10)–NiO > MnOx(0.17)–NiO > MnOx(0.25)–NiO > NiO > MnOx. Table 10 shows some of the

developments on base metal catalysts.

5.4. Perovskites

The catalytic properties of perovskites were systematically studied since 1977 and these materials

have been used for the total oxidation of methane [89-90]. Perovskites are mixed oxides of general formulae

ABO3, whereas A = Lanthanide ion, and B= Transition metal ion. Perovskites type transition metal oxide

mixtures showed comparable activity, stability when properly prepared. They are attractive with respect to

noble metals because of their lower cost and the absence of problems such as sublimation and volatilization.

The perovskite structure allows for a number of substitutions i.e. partial substitution of either A or B cation

and compositional modifications, so that different oxidation states for the transition metal are possible, as

well as anionic or cationic defectivity [91]. Considerable amount of work has been done on perovskites in

order to enhance the catalytic activity of the structures [23, 93, 94]. According to the data accumulated in

literature complete oxidation of CH4 takes place at temperature of 600 °C or above [16]. This is a bit high

when compared with other catalysts i.e noble or base metal catalysts.

Surface area plays a major role for the methane oxidation and therefore umpteen efforts have been

made to increase the surface area. Considerable efforts have been done by Kaliaguine and colleagues [23]

for developing new sized high surface area of 100 m2/g using high energy milling. The process is simple,

efficient, inexpensive and does not require any heating step for producing a perovskite that may easily show

a very high specific surface area. Another advantage is that the obtained perovskite has a high density of

lattice defects thereby showing a higher catalytic activity. Series of perovskites have been reported [16] for

methane conversion which increases the surface area and hence the catalytic activity using gold in the

substitution of La, instead of Sr, in LaFeO3 and LaFe0.5Co0.5O3 perovskite oxides, at low temperature (below

700 °C). Series of many efforts have been done using many metals [95-96]. However, when compared with

other catalysts; catalytic activity, poisoning, low surface area are some of the other facts where perovskites

cannot withstand with the other catalysts [93]. Gold was also depicted in many perovskites for increasing

the activity of the catalyst. Chaudhary [16] reported series of perovskites for methane conversion in which

Ag was doped in substitution of La in LaFeO3 and LaFe0.5Co0.5O3 perovskite. This causes large increase in

the catalytic activity of the perovskite in the complete combustion of methane. Ag-doped LaFe0.5Co0.5O3



shows the highest methane combustion activity i.e. T100%=670°C. Table 11 depicts some of the advances

on perovskites catalysts.

Table 11. Accumulated literature on perovskites for methane oxidation


Exp Operating

Parameters

Remark Ref

Pd/ZrO2,

Pd/LaMnO32ZrO2

Solution combustion synthesis

(SCS),

Calc. temp. 900 °C

0.1 g, U-shaped quartz

tube, 50 cm3/min, CH4

(2%), O2 (14%) and He

(balance)

Pd/LaMnO32ZrO2

Shows T50%=375°C

T90%=425°C, T100%=475°C

[97]

La0.9FeO2.85,

La0.8FeO2.70,

La0.7FeO2.55,

LaFeO, low-temperature thermal

decomposition,

Calc. temp. 473 K

400 mg, tubular

continuous flow,

30mL/min,

CH4 and O2 (ratio 1:6)

At temp. of 748 La0.9FeO2.85

shows T34%,

La0.8FeO2.70 shows T30%,

La0.7FeO2.55 shows T25%,

LaFeO shows T20%

[96]

LaMnO3 ,

LaMnO3·17MgO

combustion synthesis

0.05 g, quartz reactor,

2% CH4, 8% O2 and

N2.

LaMnO3·17MgO shows

T50%= 526 °C,

LaMnO3 shows 461°C

[95]

Ce1-xLaxO2-x/2/

Al2O3/FeCrAl, monolith catalysts,

where x varies from 0 to 1. Calc.

temp. 500 °C

quartz flow reactor,

2 vol.% CH4 in air,

SV= 7802, 15,604 and

31,208 mL/g

Ce1-xLaxO2-x/2/ Al2O3/FeCrAl

shows T50%=550 °C, T100%=700

°C.

[98]

LaAl1-xFexO3(0<X<1), citerate,

calc. temp. 800 °C

0.4 g, 0.4%

CH4, 10% O2, and N2

as balance, SV=

40,000 cm3 STP h-1 g-1

Catalyst with x=0.6 shows

T50%=800 °C, T100%=950 °C.

[18]

LaFeO3,

LaFe0.5Co0.5O3,

La0.7 Sr (or Ag)0.3FeO3 and La0.7Sr

(or Ag)0.3Fe0.5Co0.5O3

Co-precipitation,

Calc. b/w 750-900 °C.

0.1 g, quartz micro-

reactor, 4 mol%

methane in air, SV= 51

000 cm3/g h.

La0.7Sr (or Ag)0.3Fe0.5Co0.5O3

and La0.7 Sr (or Ag)0.3FeO3

shows T100%=700 °C

[16]

LaMnO3

La2O3/Al2O3MgO

30% LaMnO3/(5% La2O3/Al2O3)

quartz down flow

reactor,

0.4 vol% CH4 and 10

30% LaMnO3/(5%

La2O3/Al2O3) shows T100%=650

°C

[17]



20% LaMnO3/MgO

30% LaMnO3/(5% La2O3/Al2O3)

20% LaMnO3/MgO,

Calc. temp. of 800 and 1100 °C

vol.% O2 remaining

gas being nitrogen,

Flow rate 0.09 g s/N

cm3.

whereas 20% LaMnO3/MgO

exhibits T100%=625 °C

6. METHANE OXIDATION OVER COBALT BASED CATALYST

6.1 Early progress in catalyst development

Exploration of cobalt based catalysts started in nineteenth century [101] and is still in the

development process [102]. Apart from oxidation/ combustion, various advance studies have been made on

cobalt supported catalyst. Such as synergistic effect [103], effect of modification (supported and

unsupported catalyst) [13, 14, 15] and new synthesis methods [104], nano-particles exhibit promising

catalytic activities [105]. Cobalt has been extensively studied particularly for the purification of automotive

exhaust which has been depicted in several reports [106, 55].

6.2 Catalyst Activity and Stability of cobalt based catalyst

Bray et al. in 1920 [107] investigated many cobalt based catalysts for the first time for CO

oxidation. Since then the catalytic behaviour of a number of Cobalt based catalyst for methane oxidation

have attracted much interest. Among the catalyst for methane oxidation, cobalt based catalyst has received

a lot of attention due to its remarkable properties, such as moderate saturation magnetization, relatively

large magnetic anisotropy, high Curie temperature, incredible mechanical hardness, excellent chemical

stability and last but not least low price. Many patents were filed [71] in early stage of catalyst development

for use as exhaust control catalyst for internal combustion engine. Many researchers [108] around the globe

tested and explored cobalt based catalyst and found that it is a best suited catalyst for methane oxidation.

Cobalt is very active for CO oxidation even at temperature of -77°C [109]. However according to the

literature data minimum temperature required for methane oxidation is around 550°C [110, 103]. McCarty

et al. 1997 [111] studied specific rates for catalytic combustion of dilute methane on various oxides and it

was demonstrated that activity for methane combustion with the supported oxides follows the order: PdO

> RuO2 > Co3O4 > CuO > NiO > Fe2O3 > Mn2O3 > Cr2O3.

A recent work reported by Raluca et al. [104] argued that cobalt is a rival of platinium based catalyst

for methane oxidation. In their work they demonstrated that the two oxides CoFe2O4 (I) and CoFe2O4 (II)

show same activity as that of platinum based catalyst (1% wt. Pt/Al2O3) [104]; also in terms of stability

CoFe2O4 (II) is equally stable as that of 1% wt. Pt/Al2O3. Further the work of Fino and colleagues [112]

on CNG exhaust emissions on various Spinel-type-oxide catalysts states that cobalt (CoCr2O4) comes out

to be the best catalyst among the other catalysts i.e. activity varies as CoCr2O4 > MnCr2O4 > CoFe2O4 >

MgFe2O4. Cobalt is also reported on various supports for methane oxidation [103]. Xiao et al. [103]

prepared series of cobalt-based catalysts with different supports for methane oxidation, the supports used

are TiO2, Al2O3, MgO, and ZrO2 and it was demonstrated that ZrO2 supported cobalt catalyst (1% Co) was

found to have the highest activity amongst other supported and bulk Co3O4 catalysts. Whereas, tremendous

results in terms of activity of cobalt based catalyst, the author has described the Influence of cobalt precursor

and fuels on the performance of combustion synthesized Co3O4/γ-Al2O3 catalyst for methane oxidation

[113]. A series of nanosized Co3O4/γ-Al2O3 catalysts have been prepared using a combination of wetness

impregnation, the obtained catalyst has complete conversion of methane in between 400–425°C which is

very less in comparison with other catalyst prepared by traditional methods. Moreover the stability of the



catalyst was also not disturbed as after two days of catalytic performance, no considerable deactivation of

combustion-synthesized catalysts was observed and their particle size remained the same. A recent work,

demonstrated that the addition (Co/Sm molar ratio=0.98/0.02 and 0.95/0.05) of samarium (Sm) increased

the activity of spinel Co3O4 catalyst for CH4 oxidation prepared by co-precipitation method. The complete

conversion of methane takes place at temperature of 450°C [102].

6.3 Characterization studies on cobalt based catalyst

In order to elucidate the relationship between the performance and its physico-chemical properties

of catalyst, characterisation of the catalyst is a fundamental step which provides various parameters.

Characterization includes textural properties like surface area (N2 adsorption), pore volume and pore size

distribution [49], active surface area, and dispersion of active components (chemisorptions) [114], phase

identification (X-ray Diffraction, XRD) [115], surface composition (XPS), redox properties (temperature

programmed reduction/oxidation, TPR/TPO) [114], morphology (scanning electron microscopy-electron

dispersive spectroscopy, SEM-EDS/transmission electron microscopy, TEM) [116] etc. All of these

properties help in better understanding of the catalyst.

Surface area, pore volume and pore size distribution is important tool in determining the activity

of particular catalyst moreover with variation of these three parameters activity can be increased or

decreased and hence can be modified accordingly. A study reports that the catalyst (Co3O4/samarium)

prepared by co-precipitation method and characterization was done by various techniques such as N2

adsorption-desorption with Brunauer-Emmett-Teller technique (N2-BET), X-ray powder diffraction (XRD),

thermal gravity analysis differential scanning calorimetry (TGA-DSC), H2 temperature programmed

reduction (H2-TPR) and X-ray photoelectron spectroscopy analysis (XPS). BET specific surface areas of

pure Co3O4 was observed about 20 m2/g, pore volume of 0.24 cm3/g and crystalline size of 65 nm. Moreover

the addition of samarium increased all these parameters i.e. BET becomes for sample having molar ration

of 0.90/0.10, BET specific surface areas becomes 75 m2/g, pore volume of 0.38 cm3/g and crystalline size

of 21 nm [102]. However the characterization results shown by Miao et al. [49] of Au–Pt/Co3O4 and Au–

Pd/Co3O4 catalyst prepared by co-precipitation technique, reveals some of the different from Xu et al. [102].

Pure Co3CO4 have BET surface area of 57.1 m2/g. The surface area increases tremendously to 139.8 m2/g

with the addition (1.58%) of palladium to Co3CO4. Calcinations temperature plays an important role in the

physio-chemical properties of the catalyst.

6.4 Cold Start Emission Control

Several studies confirmed that during the cold start phase of the engine, unburned HCs, CO is

emitted even if the vehicle is fitted with TWC [117-118]. Cold start is that phase, when the engine is just

turned on i.e. when the temperature of the tailpipe or engine is under transformation phase between ambient

temperature and fully warmed up condition. It has been also concluded that the extra emissions of cars

during cold start period depend on three major parameters: 1) The combustion principle (diesel/gasoline);

2) The ambient temperature which is considered to be equal to the vehicle’s temperature at test start; and

3) The test cycle driven [117]. Further Cold start extra emissions can be subdivided into two parts: (i) excess

emissions due to the starting of the engine and (ii) excess emissions during the warming-up process of the

engine and the catalyst [119]. The extent of this cold-start phase is also dependent on the characteristics of

the vehicle.

During cold start, TWC is totally inactive; because the catalytic converter has not yet warmed up

i.e TWC has not attained light-off temperature which is required (350°C) for catalytic conversion of CO



and HCs. TWC will not be able to function effectively until it reaches the light-off temperature as the

conversion efficiency depends strongly on the working temperature and is practically zero during the

starting and warming up period. Vehicles equipped with TWCs in catalytic converters presently are able to

achieve the reductions of CO, NOx and unburned HCs. However these emissions are reduced up to 95%

when TWC is fully warmed up [120]. Together, these two important factors are responsible for the higher

tailpipe emissions during the cold-start phase. The extent of this cold-start phase is also dependent on the

outside temperature and characteristics of the vehicle. Cobalt based catalysts can oxidise CO even at the

temperature of -77°C [109] which is a paramount in vehicular industry. Cobalt is reported by numerous

authors for its oxidation ability even at low temperature [73]. Thus it can be used in TWC converter to

overcome the problem of cold start phase.

7. CATALYST DEACTIVATION

Deactivation refers to loss of activity of the catalyst with time. This time can vary from a few

minutes for a laboratory catalyst to 150,000 miles duration for an auto-exhaust catalyst. Deactivation is a

complex phenomenon as it depends upon number of parameters such as poisoning, fouling, thermal

degradation (sintering, evaporation) initiated by the often high temperature, mechanical damage and

corrosion/leaching etc [122]. Catalyst activity and stability plays an important role in three-way catalysis

because it controls the economics of the vehicular industry. Loss of catalyst activity can occur due to loss

of the catalytically active surface, the change in the metal surface, changes in the catalyst structure or may

be the combination of all three[123]. Numerous parameters are responsible for the deactivation of the

catalyst however they can be described in terms of Mechanical, Chemical and Thermal phenomenon as

described in Table 12.

Table 12. Cause of catalyst deactivation [124]

Type Cause Results

Mechanical Particle failure channelling, plugging

Fouling Loss of surface

Thermal Component volatization Loss of component

Phase changes Loss of surfaces

Compound formation Loss of component and surface

Sintering Loss of surface

Chemical Poison adsorption Loss of active sites

Coking Loss of surface, plugging

7.1. Thermal Deactivation and Stability

Loss of activity in metal catalysts via loss of surface area owing to sintering is a universal

phenomenon. Hughes [125] gave the following increasing order of stability for metals:

Ag < Cu < Au < Pd < Fe < Ni < Co < Pt < Rh < Ru < Ir < Os < Re.

Lower the metal is in this series the more troublesome deactivation by sintering will be and the more care

has to be taken to minimize the effect. For example, it is not surprising that copper based catalysts are more

susceptible to sintering than the cobalt and nickel catalysts used in various oxidation or hydrogenation

process. Generally a minimum of 1m2/g surface area is required for useful field application.



7.2. Chemical Poisoning

Catalyst deactivation is inevitable; it occurs when the poison molecule becomes reversibly or

irreversibly chemisorbed to active sites. The poisoning molecule may be a reactant, by-product or product

in the main reaction or it may be an impurity in the feed stream. For example water is produced during the

catalytic oxidation of methane, which sticks to the number of active site and inhibits the reaction [77]. This

decreases the surface area of catalyst available for reaction so more un-reacted pollutants such as NOx, CO,

and hydrocarbons are released into the atmosphere. However the data presented in literature is contradictory

sometimes [77]. Other catalyst poisons include manganese, silicone, phosphorus, and zinc [126].

Li [77] studied promoting effect of water vapor on catalytic oxidation of methane over

cobalt/manganese mixed oxides water vapour. When 5% water vapour is introduced into the reaction feed,

methane conversion on MnOx decreased from 47 to 41% at 500°C, whereas only minor changes were

observed on CoOx catalyst under the similar conditions. However, it was found that a remarkable increase

in methane conversion (70 to 83%) was observed on the CoMn and CoMn2 catalysts when water vapour

(5%) was introduced into the feed gas.

Sulphur is the most problematic among all the other poisons [127] and is usually found in all

commercially available fuels as an impurity. It is reported that concentration of around 150 ppm sulphur

present in fuel, gives an exhaust concentration of around 10 ppm of sulphur [127]. The decrease in

concentration is due to chemical poisoning in the engine converting Sulphur to SO2.

8. EFFECT OF CATALYST PREPARATION PARAMETERS ON CATALYTIC ACTIVITY

8. 1 Cobalt as a support

Liotta et al. did extensive study devoted to cobalt catalyst in a series of publications. In 2005, Liotta

et al. [13] prepared Gold-based catalysts supported on cobalt oxide (Co3O4), Ceria (CeO2) and mixed oxides

(Co3O4–CeO2) using co-precipitation method for methane oxidation. It was demonstrated that Au supported

on Co3O4 was the most active for total oxidation of methane i.e. T100%=600°C. The activity of the catalysts

was described i.e. the presence of Co2+ and Co3+ ions are active sites for methane activation whereas CeO2

in AuCoCe plays the role of a structural promoter. Further cobalt-ceria catalyst was tested for methane

oxidation by the same author [14] over Co3O4/CeO2 composite oxides with different cobalt loading (5, 15,

30, 50, 70 wt.% as Co3O4) prepared by co-precipitation method. Complete oxidation of methane takes place

at 750°C by composite catalyst containing 30% by weight of Co3O4 ( Co and Ce in atomic ratio close to

1:1) which is bit higher in comparison to the gold based catalyst. Furthermore, the optimised catalyst of

same composition prepared by co-precipitation method was again reported for methane oxidation but in

cordieritic Honeycomb support with Pd/Pt for methane oxidation [81]. The bimetallic, Pd–Pt catalyst

obtained by impregnation of the supported Co3O4 (30%)–CeO2 (70%) with Pd and Pt with total metal

loading of 50 g/ft3. However the addition of palladium and platinum does not cause much change in the

complete combustion of methane as the conversion temperature is not reduced significantly.

Junhua Li et al. 2009 [52] prepared manganese cobalt oxides by co-precipitation method with

different Co/Mn ratios for methane combustion. A significant improvement in the conversion temperature

for methane oxidation was achieved i.e. T100%=360°C in comparison to the previous reported cobalt catalyst.

This low oxidation temperature was observed for cobalt –manganese catalyst (Co/Mn molar ratio of 5:1).

The increase in catalytic activity of the catalyst is due to manganese (as the dopant), which caused disorder

in the spinel structure of cobalt oxides. This disorder consequently enhanced the activity of the reactive

ions in the octahedral sites and probably facilitated the de-hydroxylation steps, thus leading to increase in

the catalytic performance of the Co/Mn mixed oxides.



8.2 KINETICS OF CH4 OXIDATION OVER COBALT BASED CATALYST

The typical graph of conversion of CH4 as a function of temperature of the catalyst bed is shown

in Figure 3, with three distinct regions, viz. kinetic controlled region-X, light-off region-Y (uncontrolled)

and steady state operation (diffusion controlled) region-Z.

In the first region-X (area X in Fig. 3), the rate of reaction increases relatively slowly with increasing

temperature and the rate is controlled by the kinetics of the chemical reaction. The reaction occurs only on

the catalyst surface in this region and the catalyst performance is dictated by its intrinsic activity. A further

increase in temperature leads to an exponential increase in rate (area Y in Fig. 3) to the point where heat

generated by combustion is much greater than heat supplied as a result of rapid exothermic CH4 oxidation.

Beyond region-Y oxidation reaction continues with increasing temperature and the system regains a self-

sustained steady state region-Z (area Z in Fig. 3) at very high conversion. In this region mass transfer of

gases to the catalysts is the rate determining step. One important factor in the catalytic combustion of

Methane is ‘light off’. This can be defined in various ways but refers to the temperature at which mass

transfer control becomes rate controlling. Because of the shape of the curve (Fig. 3), the definition of light-

off temperatures as the temperature at which conversion reaches 10%, 20% or 50% makes little difference.

The kinetic analysis involves exclusive data corresponding to conversions below 10-15%, therefore in order

to establish kinetic model various Light-off curves are required [128]. Moreover ideal plug flow conditions

are required in packed bed reactor to generate meaningful kinetic data otherwise the data is of no use [129,

130].

Figure 3. Effect of Temperature on Methane Oxidation [103]

A number of kinetic studies have been conducted on various cobalt based catalysts [114, 121, 106,

71]. The steady-state values of methane and oxygen partial pressures are used to describe the kinetics of

methane oxidation over the catalysts studied. Various correlations are available for the calculation of

average methane reaction rate. However the information available in the literature on the kinetics is often

conflicting. The reaction is reported to be of the first order or less in CH4 concentration (partial pressure).

Because of overheating as a result of high conversions of methane, chemical kinetics are often affected by

mass and heat transfer [55]. Below given are some re-arranged correlations for the evaluation of reaction

rate [121].

W𝑐𝑎𝑡

FCH4,0

= ∫ 𝑑𝑋𝐶𝐻4

−𝑟𝐶𝐻4

𝑋𝐶𝐻4,𝑜𝑢𝑡𝑋𝐶𝐻4,𝑖𝑛

= 1

(−𝑟𝐶𝐻4)𝑎𝑣𝑔 ∫ 𝑑𝑋𝐶𝐻4

𝑋𝐶𝐻4,𝑜𝑢𝑡𝑋𝐶𝐻4,𝑖𝑛

= 𝑋𝐶𝐻4,𝑜𝑢𝑡

− 𝑋𝐶𝐻4,𝑖𝑛

(−𝑟𝐶𝐻4)𝑎𝑣𝑔

(5)



Where Wcat is the catalyst weight (g), FCH4,in is the initial methane flow-rate (mol/min), XCH4 is the

conversion of methane, and -rCH4 is the rate of methane reaction. Many researchers [121, 100] have reported

CH4 oxidation to be of first order as given below:

(−𝑟𝐶𝐻4)

𝑎𝑣𝑒= 𝑘𝑃𝐶𝐻4

𝛼 𝑃𝑂2

𝛽 (6)

where k is the rate constant, PCH4 is the average partial pressure of methane, PO2 is the average partial

pressure of oxygen, and 𝛼 and 𝛽 are the apparent reaction orders for methane and oxygen, respectively. A

kinetic study made by Klvana, D. et al. 1994 [99] for methane combustion over cobalt perovskites, has

revealed that a simple first-order model gave a good fit to the experimental data at low temperatures of 375

to 650 oC.

𝑟𝐶𝐻4= 𝑘𝑃𝐶𝐻4

(7)

However, two-term model was also related to the reaction mechanism, but is not fruitful for the cobalt based

catalysts.

𝑟𝐶𝐻4= 𝑘1 + 𝑘2𝑃𝑂2

0.5𝑃𝐶𝐻4 (8)

9. CONCLUSION

To curb the menace of vehicular pollution, the choice of the appropriate catalyst for TWC

converters is a fundamental step in terms of activity, selectivity, durability, availability and cost, for the ever

increasing number of vehicles on roads. The use of noble metals has detrimental effects on the commercial

cost of the catalyst, so focus has recently turned to transition metal base catalysts. Cobalt based catalysts

are reasonable and appropriate in the total oxidation of methane under lean-burn conditions. It exhibits

comparable activity for CH4 oxidation to that of precious metal auto exhaust purification catalyst. Further,

it is comparatively very cheap compared to noble metals. Moreover, cobalt based catalyst can

simultaneously remove all the three major pollutants (CO, HCs and NOx) from the exhaust in the

temperature region considerably lower than flame or explosion temperatures. However the poisoning

compounds with vehicular exhaust reduce or affect the activity of the catalyst. Modification of the catalyst

with the addition of suitable support, promotor, pretreatment and advance synthesis methods would lead to

the desirable performance of cobalt based catalyst. Performance of cobalt based catalyst considerably

improved when prepared as nano-structured materials.

Although cobalt based catalyst is a well-studied catalyst, still further research is required in order

to develop this catalyst following newer routes investigated recently for oxide catalysts, suitable for

vehicular exhaust TWC converter. It is, therefore, proposed to thoroughly investigate unsupported as well

as supported cobalt based nano-sized catalysts for future application of CH4 oxidation and also in TWC

converters. The present paper opens a new horizons or opportunity for the “cobalt based catalyst” as

competitive catalysts in methane combustion reaction.

REFERENCE

[1] Bakar, Rosli A. A technical review of compressed natural gas as an alternative fuel for internal combustion

engines. American Journal of Engineering and Applied Sciences. 2008, 1 (4), 302-311.



[2] G., Munde Gopal; S. Dalu Rajendra. Compressed Natural Gas as an Alternative Fuel for Spark Ignition

Engine: A Review. International Journal of Engineering and Innovative Technology. 2012, 2(6), 92-96.

[3] Kato K.; Igarashi K.; Masuda M.; Otsubo, K. Development of Engine for Natural Gas Vehicle. SAE Technical

Paper. 1999, 1999-01-0574, doi: 10.4271/1999-01-0574.

[4] Richard Stone. Introduction to Internal Combustion Engines. 1999, 3rd Edition. Mac Millan Press Ltd.

[5] Jahirul, M. I.; Masjuki, H. H.; Saidur, R.; Kalam, M. A.; Jayed, M. H.; Wazed, M. A. Comparative engine

performance and emission analysis of CNG and gasoline in a retrofitted car engine. Applied Thermal

Engineering. 2010, 30(14), 2219-2226.

[6] Hochhauser, A., Koehl, W., Benson, J., Burns, V. Comparison of CNG and Gasoline Vehicle Exhaust

Emissions: Mass and Composition - The Auto/Oil Air Quality Improvement Research Program. 1995, SAE

Technical Paper 952507, doi:10.4271/952507.

[7] MacLean; Heather L.; Lester B. Lave; Rebecca Lankey; Satish Joshi. A life-cycle comparison of alternative

automobile fuels. Journal of the air & waste management association. 2000, 50 (10), 1769-1779.

[8] Gélin, Patrick; Primet, Michel. Complete oxidation of methane at low temperature over noble metal based

catalysts: a review. Applied Catalysis B: Environmental. 2002, 39 (1), 1-37.

[9] Choudhary, V. R.; Patil, V.P.; Jana P.; Uphade B.S. Nano-gold supported on Fe2O3: A highly active catalyst

for low temperature oxidative destruction of methane green house gas from exhaust/waste gases. Applied

Catalysis A: General. 2008, 350 (2), 186-190.

[10] Grisel, R. J. H.; Nieuwenhuys, B.E. A comparative study of the oxidation of CO and CH4 over

Au/MOx/Al2O3 catalysts. Catalysis today. 2001, 64 (1), 69-81.

[11] Bozo, Christine; Nolven Guilhaume; Jean-Marie, Herrmann; Role of the ceria–zirconia support in the

reactivity of platinum and palladium catalysts for methane total oxidation under lean conditions. Journal of

Catalysis. 2001, 203 (2), 393-406.

[12] Groppi, G.; Cristiani, C.; Lietti, L.; Ramella,C.; Valentini,M.; Forzatti,P. Effect of ceria on palladium

supported catalysts for high temperature combustion of CH4 under lean conditions. Catalysis Today. 1999,

50 (2), 399-412.

[13] Liotta, L. F.; Carlo, G. Di; Pantaleo, G.; Deganello, G. Co3O4/CeO2 and Co3O4/CeO2–ZrO2 composite

catalysts for methane combustion: Correlation between morphology reduction properties and catalytic

activity. Catalysis Communications.2005, 6 (5), 329-336.

[14] Liotta, L. F.; Carlo, G. Di; Pantaleo, G.; Deganello, G. Catalytic performance of Co3O4/CeO2 and

Co3O4/CeO2-ZrO2 composite oxides for methane combustion: Influence of catalyst pretreatment temperature

and oxygen concentration in the reaction mixture. Applied Catalysis B: Environmental. 2007, 70 (1-4), 314-

322.

[15] Liotta, L. F.; Carlo, G. Di; Longo, A.; Pantaleo, G.; Venezia, A. M. Support effect on the catalytic

performance of Au/Co3 O4–CeO2 catalysts for CO and CH4 oxidation. Catalysis Today. 2008, 139(3), 174-

179.

[16] Choudhary, V. R.; Uphade, B. S.; Pataskar, S. G. Low temperature complete combustion of methane over

Ag-doped LaFeO3 and LaFe0.5Co0.5O3 perovskite oxide catalysts. Fuel. 1999, 78 (8), 919-921.

[17] Cimino, S.; Lisi, L.; Pirone, R; Russo, G.; Turco, M. Methane combustion on perovskites-based structured

catalysts. Catalysis today, 2000, 59 (1), 19-31.

[18] Ciambelli, P.; Cimino, S.; Lasorella, G.; Lisi, L.; Rossi, S. De; Faticanti, M.; Minelli, G.; Porta, P. CO

oxidation and methane combustion on LaAl1− xFexO3 perovskite solid solutions. Applied Catalysis B:

Environmental. 2002, 37 (3), 231-241.

[19] Choudhary, T. V.; Banerjee, S.; Choudhary, V. R. Catalysts for combustion of methane and lower

alkanes. Applied Catalysis A: General. 2002, 234 (1), 1-23.

[20] Walther, Guido. Methane oxidation on supported gold catalysts. PhD dissertation, Center for

Nanotechnology, Technical University of Denmark, 2008.

[21] Gersen, Sander. Experimental study of the combustion properties of methane/hydrogen mixtures. PhD

dissertation University of Groningen, Nijenborgh, Netherlands, 2007.



[22] Choudhary, V. R.; Mamman, A. S.; Rajput, A. M.; Uphade, B. S. Patent No. 5,744,419. Washington, DC:

U.S, 1998.

[23] Kaliaguine, S.; Van Neste, A. U.S. Patent No. 6,017,504. Washington, DC: U.S., 2000.

[24] Sera, M.A.; Bakar, R.A.; Leong, S.K. CNG engine performance improvement strategy through advanced

intake system. SAE Technical Paper, 2003, 2003-01-1937.

[25] Pischinger, S.; Umierski, M.; Hüchtebrock, B. New CNG concepts for passenger cars: High torque engines

with superior fuel consumption, SAE Technical Paper, 2003, 2003-01-2264.

[26] EPA. Methane and Nitrous Oxide Emissions from Natural Sources. U.S. Environmental Protection Agency,

Washington, DC, USA, 2010.

[27] Raine, R., Zhang, G., and Pflug, A. Comparison of Emissions from Natural Gas and Gasoline Fuelled

Engines - Total Hydrocarbon and Methane Emissions and Exhaust Gas Recirculation Effects. SAE Technical

Paper. 1997, 970743, doi:10.4271/970743.

[28] Shudo, T.; Shimamura, K.; Nakajima, Y. Combustion and emissions in a methane DI stratified charge engine

with hydrogen pre-mixing. JSAE Review, 2000, 21(1), 3-7.

[29] Bachelet, D.; Neue, H. U. Methane emissions from wetland rice areas of Asia. Chemosphere, 1993, 26(1),

219-237.

[30] Parashar, D. C.; Gupta, P. K.; Rai, J.; Sharma, R. C.; Singh, N. Effect of soil temperature on methane

emission from paddy fields. Chemosphere, 1993, 26(1), 247-250.

[31] Keppler, Frank; Hamilton, John TG; Braß, Marc; Röckmann, Thomas. Methane emissions from terrestrial

plants under aerobic conditions. Nature. 2006, 439(7073), 187-191.

[32] Crutzen, Paul J.; Aselmann, Ingo; Seiler, Wolfgang. Methane production by domestic animals, wild

ruminants, other herbivorous fauna, and humans. Tellus. 1986, 38B, 271-284.

[33] Lipman, Timothy E.; Delucchi, Mark A. Emissions of nitrous oxide and methane from conventional and

alternative fuel motor vehicles. Climatic Change, 2002, 3 (4), 477-516.

[34] Migeotte M.J., Spectroscopic evidence of methane in the earth’s atmosphere, Phys. Rev. 1948, 73, 519–520.

[35] Moss, A. R.; Jouany, J. P.; Newbold, J. Methane production by ruminants: its contribution to global warming.

Amin. Res. 2000, 49 (3), 231-254.

[36] Emissions Control Manufacturers Association 2010 http:/ecmaindia.in (accessed January 22, 2012)

[37] ARAI. The automotive research association of India, (2011).

[38] Viktorin, K., Hälsorisker. Swedish Environmental Protection Agency. 1993, Report 4223.

[39] Bosteels, D.; Searles, R.A. Exhaust Emission Catalyst Technology: New Challenges and Opportunities in

Europe. Platinum Metals Rev. 2002, 46(1), 27–36.

[40] Wendland, D. and Matthes, W. Visualization of Automotive Catalytic Converter Internal Flows. SAE

Technical Paper. 1986, 861554, doi:10.4271/861554.

[41] Heck, Ronald M.; Farrauto, Robert J. Automobile exhaust catalysts. Applied Catalysis A: General. 2001,

221 (1), 443-457.

[42] Bond, G. C. The catalytic properties of gold. Gold Bulletin, 1972, 5 (1), 11-13.

[43] Anderson, C.; Kupe, J.; LaBarge, W. J. U.S. Patent No. 7,094,730. Washington, DC, 2006.

[44] Fujdala, Kyle L.; Jia, Jifei; Truex, Timothy J. Engine exhaust catalysts containing palladium-gold. U.S.

Patent no.7,709,414. Washington, DC, 2010.

[45] Waters, R. D.; Weimer, J. J.; Smith, J. E. An investigation of the activity of coprecipitated gold catalysts for

methane oxidation. Catalysis letters. 1994, 30 (1-4) 181-188.

[46] Hereijgers, Bart PC; Weckhuysen, Bert M. An attempt to selectively oxidize methane over supported gold

catalysts. Catalysis letters. 2011, 141 (10) 1429-1434.

[47] Haruta, Masatake; Yamada, N.; Kobayashi, T.; Iijima, S. Gold catalysts prepared by coprecipitation for low-

temperature oxidation of hydrogen and of carbon monoxide. Journal of Catalysis. 1989, 115 (2), 301-309.

[48] Solsona, B. E.; Garcia, T.; Jones, C.; Taylor, S. H.; Carley, A. F.; Hutchings, G. J. Supported gold catalysts

for the total oxidation of alkanes and carbon monoxide. Applied Catalysis A: General. 2006, 312, 67-76.



[49] Miao, S.; Deng, Y. Au–Pt/Co3O4 catalyst for methane combustion. Applied Catalysis B: Environmental.

2001, 31(3), L1-L4.

[50] Ivanova, S.; Petit, C.; Pitchon, V. "A new preparation method for the formation of gold nanoparticles on an

oxide support." Applied Catalysis A: General. 2004, 267 (1), 191-201.

[51] Blick, Keith; Mitrelias, Thanos D.; Hargreaves, Justin SJ; Hutchings, Graham J.; Joyner, Richard W.; Kiely,

Christopher J.; Wagner, Fritz E. Methane oxidation using Au/MgO catalysts. Catalysis letters. 1998, 50(3),

211-218.

[52] Li, Junhua; Liang, Xi; Xu, Shicheng; Hao, Jiming. Catalytic performance of manganese cobalt oxides on

methane combustion at low temperature. Applied Catalysis B: Environmental. 2009, 90 (1), 307-312.

[53] Zhang, Y.; Jiguang D.; Lei, Z.; Wenge, Qiu; Hongxing Dai; Hong He. AuOx/Ce0.6Zr0.3 Y0.1O2 nano-sized

catalysts active for the oxidation of methane. Catalysis Today. 2008, 139(1), 29-36.

[54] Machocki, A.; Ioannides, T.; Stasinska, B.; Gac, W.; Avgouropoulos, G.; Delimaris, D.; Pasieczna, S.

Manganese–lanthanum oxides modified with silver for the catalytic combustion of methane. Journal of

Catalysis. 2004, 227(2), 282-296.

[55] Lee, Joo H.; Trimm, David L. Catalytic combustion of methane. Fuel processing technology. 1995, 42 (2),

339-359.

[56] Geus, John W.; Joep, C.; Giezen, Van. Monoliths in catalytic oxidation."Catalysis Today. 1999, 47 (1), 169-

180.

[57] Eguchi, K.; Arai, H. Low temperature oxidation of methane over Pd-based catalysts effect of support oxide

on the combustion activity. Applied Catalysis A: General. 2001, 222(1), 359-367.

[58] Yao, H. C.; Yao, Y. Fu. Ceria in automotive exhaust catalysts: I. Oxygen storage. Journal of Catalysis. 1984,

86(2), 254-265.

[59] Xiao, L. H.; Sun, K. P.; Xu, X. L.; Li, X. N. Low-temperature catalytic combustion of methane over Pd/CeO2

prepared by deposition–precipitation method. Catalysis Communications. 2005, 6(12), 796-801.

[60] Simplício, Lílian MT; Brandão, Soraia T.; Domingos, Daniela; Bozon-Verduraz, François; Emerson, A.

Sales. Catalytic combustion of methane at high temperatures: Cerium effect on PdO/Al2O3 catalysts. Applied


[61] Thevenin, Philippe O.; Alcalde, Ana; Pettersson, Lars J.; Järås, Sven; Fierro, José L. G. Catalytic combustion

of methane over cerium-doped palladium catalysts. Journal of Catalysis. 2003, 215 (1), 78-86.

[62] Persson, Katarina; Anders, Ersson; Jansson, K.; Iverlund, N.; Järås, Sven. Influence of co-metals on

bimetallic palladium catalysts for methane combustion. Journal of Catalysis. 2005, 231(1), 139-150.

[63] Sekizawa, K.; Widjaja, H.; Maeda, S.; Ozawa, Y.; Eguchi, K. Low temperature oxidation of methane over

Pd/SnO2 catalyst. Applied Catalysis A: General. 2000, 200(1), 211-217.

[64] Ciuparu, D.; Katsikis, N.; Pfefferle, L. Temperature and time dependence of the water inhibition effect on

supported palladium catalyst for methane combustion. Applied Catalysis A: General. 2001, 216(1), 209-215.

[65] Muto, K. I.; Katada, N.; Niwa, M. Complete oxidation of methane on supported palladium catalyst: Support

effect. Applied Catalysis A: General. 1996, 134(2), 203-215.

[66] Pecchi, G.; Reyes, P.; Concha, I.; Fierro, J. Methane Combustion on Pd/SiO2 Sol Gel Catalysts. Journal of

Catalysis. 1998, 179 (1), 309-314.

[67] Hoflund, G. B.; Li, Z. Surface characterization study of a Pd/Co3O4 methane oxidation catalyst. Applied

Surface Science. 2006, 253(5), 2830-2834.

[68] Yoshida, H.; Nakajima, T.; Yazawa, Y.; Hattori, T. Support effect on methane combustion over palladium

catalysts. Applied Catalysis B: Environmental. 2007, 71(1), 70-79.

[69] Qiao, D.; Lu, G.; Mao, D.; Liu, X.; Li, H.; Guo, Y.; Guo, Y. Effect of Ca doping on the catalytic performance

of CuO2 catalysts for methane combustion. Catalysis Communications. 2010, 11(9), 858-861.

[70] Kumar, Sasi; Nayek, M.; Kumar, A.; Tandon, A.; Mondal, P.; P. Vijay; Bhangale, U. D.; Tyagi, D. Aldehyde,

Ketone and Methane emissions from motor vehicle exhaust: a critical review. American Chemical Science

Journal. 2011, 1 (1), 1-27.



[71] Anderson, R. B.; Stein, K. C.; Feenan, J. J.; Hofer, L. J. E. Catalytic oxidation of methane. Industrial &

Engineering Chemistry. 1961, 53(10), 809-812.

[72] Zhang, Y.; Qin, Z.; Wang, G.; Zhu, H.; Dong, M.; Li, S.; Wang, J. Catalytic performance of MnOx–NiO

composite oxide in lean methane combustion at low temperature. Applied Catalysis B: Environmental. 2013,

129, 172-181.

[73] Chen, J.; Zhang, X.; Arandiyan, H.; Peng, Y.; Chang, H.; Li, J. Low temperature complete combustion of

methane over cobalt chromium oxides catalysts. Catalysis Today. 2013, 201, 12-18.

[74] IPCC, intergovernmental panel on climate change, 2013.

[75] Bremer, N. J.; Dolhyj, S. R.; Milberger, E. C. U.S. Patent No. 4,002,650. Washington, DC, 1977.

[76] Chen, J.; Shi, W.; Li, J. Catalytic combustion of methane over cerium-doped cobalt chromite

catalysts. Catalysis Today. 2011, 175(1), 216-222.

[77] Li, Weibin; Ying, Lin; Yu, Zhang. Promoting effect of water vapor on catalytic oxidation of methane over

cobalt/manganese mixed oxides. Catalysis today. 2003, 83 (1), 239-245.

[78] Artizzu, Duart P.; Brullé, Y.; Gaillard, F.; Garbowski, E.; Guilhaume, N.; Primet, M. Catalytic combustion

of methane over copper-and manganese-substituted barium hexaaluminates. Catalysis today. 1999, 54(1),

181-190.

[79] Jiang, Z.; Yu, J.; Cheng, J.; Xiao, T.; Jones, M. O.; Hao, Z.; Edwards, P. P. Catalytic combustion of methane

over mixed oxides derived from Co–Mg/Al ternary hydrotalcites. Fuel Processing Technology. 2010, 91(1),

97-102.

[80] Shi, Limin; Wei Chu; Fenfen Qu; Shizhong Luo. Low-temperature catalytic combustion of methane over

MnOx–CeO2 mixed oxide catalysts: Effect of preparation method. Catalysis letters. 2007, 113 (1), 59-64.

[81] Liotta, L. F.; Carlo, G. Di; Pantaleo, G.; Deganello, G.; Borla, E. M.; Pidria, M. Honeycomb supported

Co3O4/CeO2 catalyst for CO/CH4 emissions abatement: Effect of low Pd–Pt content on the catalytic activity.

Catalysis Communications. 2007, 8 (3), 299-304.

[82] Marion, Marie C.; Edouard, Garbowski; Michel, Primet. Physicochemical properties of copper oxide loaded

alumina in methane combustion. Journal of the Chemical Society, Faraday Transactions. 1990, 86 (17),

3027-3032.

[83] Leitenburg, Carlaáde. CeO2-based solid solutions with the fluorite structure as novel and effective catalysts

for methane combustion. Journal of the Chemical Society, Chemical Communications. 1999, 9, 965-966.

[84] Ulla, M. A.; Spretz, R.; Lombardo, E.; Daniell, W.; Knözinger, H. Catalytic combustion of methane on

Co/MgO: characterisation of active cobalt sites. Applied Catalysis B: Environmental. 2001, 29 (3), 217-229.

[85] Yuan, Xingzhou; Chen, Shaoyun; Chen, Heng; Zhang, Yongchun. Effect of Ce addition on Cr/γ-Al2 O3

catalysts for methane catalytic combustion. Catalysis Communications. 2013, 35, 36-39.

[86] Pengpanich, Sitthiphong; Vissanu, Meeyoo; Thirasak, Rirksomboon; Kunchana Bunyakiat. "Catalytic

oxidation of methane over CeO2-ZrO2 mixed oxide solid solution catalysts prepared via urea

hydrolysis." Applied Catalysis A: General. 2002, 234 (1), 221-233.

[87] Bozo, Christine; Guilhaume, Nolven; Garbowski, Edouard; Primet, Michel. Combustion of methane on

CeO2–ZrO2 based catalysts. Catalysis Today. 2000, 59 (1), 33-45.

[88] Qu, F. Fen; Wei, Chu; Li, M. Shi; Mu, H. Chen; Jin, Y. Hu. Catalytic combustion of methane over nano

ZrO2-supported copper-based catalysts. Chinese Chemical Letters. 2007, 18(8), 993-996.

[89] Luis G. Tejuca; Jose, L. G. Fierro. Structure and reactivity of perovskite-type oxides. Advances in catalysis.

1989, 36, 237-328.

[90] Seiyama, Tetsuro; Yamazoe, Noboru; Eguchi, Koichi. Characterization and activity of some mixed metal

oxide catalysts. Industrial & engineering chemistry product research and development. 1985, 24 (1), 19-27.

[91] Voorhoeve, R. J. H.; D. W. Johnson; J. P. Remeika; P. K. Gallagher. Perovskite oxides: Materials science in

catalysis. Science. 1977, 195 (4281), 827-833.

[92] IPCC, 2014: Climate Change 2014.



[93] Petrović, S.; Terlecki-Baričević, A.; Karanović, Lj; Kirilov-Stefanov, P.; Zdujić, M.; Dondur, V.; Paneva,

D.; Mitov, I.; Rakić, V. LaMO3 (M= Mg, Ti, Fe) perovskite type oxides: Preparation, characterization and

catalytic properties in methane deep oxidation. Applied Catalysis B: Environmental. 2008, 79 (2), 186-198.

[94] McCann III; Elrey L. Catalytic perovskites on perovskite supports and process for preparing them. U.S.

Patent 4,151,123, 1979.

[95] Civera, Andrea; Matteo, Pavese; Saracco, Guido; Specchia, Vito. Combustion synthesis of perovskite-type

catalysts for natural gas combustion. Catalysis Today. 2003, 83(1), 199-211.

[96] Delmastro, Alessandro; Mazza, D.; Ronchetti, S.; Vallino, Mario; Spinicci, R.; Brovetto, P.; Salis, M.

Synthesis and characterization of non-stoichiometric LaFeO3 perovskite. Materials Science and Engineering:

B. 2001, 79(2), 140-145.

[97] Civera, A.; Negro, G.; Specchia, S.; Saracco, G.; Specchia, V. Optimal compositional and structural design

of a LaMnO3/ZrO2/Pd-based catalyst for methane combustion. Catalysis today. 2005, 100 (3), 275-281.

[98] Yin, Fengxiang; Shengfu, Ji; Chen, Biaohua; Zhou, Zhongliang; Liu, Hui; Li, Chengyue. Catalytic

combustion of methane over Ce1-xLaxO2-x/2/Al2O3/FeCrAl catalysts. Applied catalysis A. 2006, 310, 164-173.

[99] Klvana, D.; J. Kirchnerova; J. Chaouki; J. Delval; W. Yaıci. Fiber-supported perovskites for catalytic

combustion of natural gas. Catalysis today. 1999, 47 (1), 115-121.

[100] Belessi, V. C.; Ladavos, A. K.; Armatas, G. S.; Pomonis, P. J. Kinetics of methane oxidation over La–Sr–

Ce–Fe–O mixed oxide solids. Physical Chemistry Chemical Physics. 2001, 3, 3856-3862.

[101] Bracconi, Pierre; Louis, C. Dufour. Hydrogen reduction of cobalt-chromium spinel oxides. I. Stoichiometric

cobalt chromite. The Journal of Physical Chemistry. 1975, 79(22) 2395-2400.

[102] Xianglan, X.U.; Hong, Han; Xiang, Wang. Promotional effects of samarium on Co3O4 spinel for CO and

CH4 oxidation. Journal of Rare Earths. 2014, 32 (2), 159-169.

[103] Xiao, T. cun; Sheng, Ji; Wang, Hai, t.; Coleman, Karl S.; Malcolm LH Green. Methane combustion over

supported cobalt catalysts. Journal of Molecular Catalysis A: Chemical. 2001, 175 (1), 111-123.

[104] Dumitru, Raluca; Florica, Papa; Ioan, Balint; Daniela, C. Culita; Cornel, Munteanu; Nicolae, Stanica;

Adelina, Ianculescu; Lucian, Diamandescu; Oana, Carp. Mesoporous cobalt ferrite: A rival of platinum

catalyst in methane combustion reaction. Applied Catalysis A: General. 2013, 467, 178-186.

[105] Hu, Linhua; Qing, Peng; Yadong, Li. Selective synthesis of Co3O4 nanocrystal with different shape and

crystal plane effect on catalytic property for methane combustion. Journal of the American Chemical Society.

2008, 130 (48), 16136-16137.

[106] Arai, H.; Yamada, T.; Eguchi, K.; Seiyama, T. Catalytic combustion of methane over various perovskite-

type oxides. Applied catalysis. 1986, 26, 265-276.

[107] Bray, W.C.; Lamb, A.B.; Frazer, J.C.W. The removal of carbon monoxide from air. The journals of

industrial and engineering chemistry, 1920, 12, 213-221.

[108] Stone, F.S. Chemisorption and Catalysis on Metallic Oxides. Adv. in Catal. 1962, 13, 1–50.

[109] Xie, Xiaowei; Yong, Li; Zhi, Q. Liu; Haruta, Masatake; Shen, Wenjie. Low-temperature oxidation of CO

catalysed by Co3O4 nanorods. Nature, 2009, 458, 7239, 746-749.

[110] Milt, V. G.; Ulla, M. A.; Lombardo, E. A. Zirconia-supported cobalt as a catalyst for methane

combustion. Journal of Catalysis. 2001, 200 (2), 241-249.

[111] McCarty, J. G.; Chang, Y. F.; Wong, V. L.; Johansson, E. M. Kinetics of high temperature methane

combustion by metal oxide catalysts. Preprints-American Chemical Society. Division of Petroleum

Chemistry. 1997, 42 (1), 158-162.

[112] Fino, Debora; Russo, Nunzio; Saracco, Guido; Specchia, Vito. CNG engines exhaust gas treatment via Pd-

Spinel-type-oxide catalysts. Catalysis today. 2006, 117 (4), 559-563.

[113] Zavyalova, U.; Scholz, P.; Ondruschka, B. Influence of cobalt precursor and fuels on the performance of

combustion synthesized Co3O4/γ-Al2O3 catalysts for total oxidation of methane. Applied catalysis. A,

General. 2007, 323, 226-233.

[114] Bahlawane, Naoufal. Kinetics of methane combustion over CVD-made cobalt oxide catalysts. Applied

Catalysis B: Environmental. 2006, 67 (3), 168-176.



[115] Jodłowski, P. J.; Kryca, J.; Iwaniszyn, M.; Jędrzejczyk, R.; Thomas, J.; Kołodziej, A.; Łojewska, J. Methane

combustion modelling of wire gauze reactor coated with Co3O4–CeO2, Co3O4–PdO catalysts. Catalysis

Today. 2013, 216, 276-282.

[116] Hu, Linhua; Qing, Peng; Yadong, Li. Selective synthesis of Co3O4 nanocrystal with different shape and

crystal plane effect on catalytic property for methane combustion. Journal of the American Chemical Society.

2008, 130, 48, 16136-16137.

[117] Weilenmann, Martin; Soltic, Patrik; Saxer, Christian; Forss, Anna M.; Heeb, Norbert. Regulated and

nonregulated diesel and gasoline cold start emissions at different temperatures. Atmospheric Environment.

2005, 39(13), 2433-2441.

[118] Liu, Shenghua; Eddy R; Cuty Clemente; Tiegang Hu; Yanjv Wei. Study of spark ignition engine fueled

with methanol/gasoline fuel blends. Applied Thermal Engineering. 2007, 27 (11), 1904-1910.

[119] Weilenmann, Martin; Favez, Jean Y.; Alvarez, Robert. Cold-start emissions of modern passenger cars at

different low ambient temperatures and their evolution over vehicle legislation categories. Atmospheric

Environment. 2009, 43 (15), 2419-2429.

[120] Please, C. P.; Hagan, P. S.; Schwendeman, D. W. Light-off behavior of catalytic converters. SIAM Journal

on Applied Mathematics. 1994, 54 (1), 72-92.

[121] Itome, Masaki; Nelson, Alan E. Methane Oxidation Over M–8YSZ andM–CeO2/8YSZ (M = Ni, Cu,

Co, Ag) Catalysts. Catalysis letters. 2006, 106 (1-2), 21-27.

[122] Moulijn, J. A.; Van, Diepen A. E.; Kapteijn, F. Catalyst deactivation: is it predictable?: What to do? Applied


[123] Spencer, Michael S.; Twigg, Martyn V. Metal catalyst design and preparation in control of deactivation.

Annu. Rev. Mater. Res. 2005, 35, 427-464.

[124] Richardson, James Thomas. Principles of catalyst development. 1989, vol. 1. New York: Plenum Press.

[125] Hughes, R. Deactivation of Catalysts; Academic Press: New York. 1994.

[126] Fogler, H.S.; Elements of Chemical Reaction Engineering, 2002, 3rd ed. Prentice Hall: Upper Saddle River,

636–637.

[127] Gandhi, H. S., GWf Graham, and R_W McCabe. "Automotive exhaust catalysis." Journal of Catalysis.

2003, 216, no. 1, pp. 433-442.

[128] Prasad, R.; Singh, Pratichi. A review on CO oxidation over copper chromite catalyst." Catal Rev: Sci &

Eng. 2012, 54, (2), 224-279.

[129] Gierman, H. Design of laboratory hydrotreating reactors: scaling down of trickle-flow reactors. Applied

Catalysis. 1988, 43 (2), 277-286.

[130] Chu, C. F.; K. M. Ng. Flow in packed tubes with a small tube to particle diameter ratio. AIChE journal.

1989, 35 (1), 148-158.

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