Adsorption and Catalysis Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology CENG 511 Lecture 3

Adsorption and Catalysis

Dr. King Lun YeungDepartment of Chemical Engineering

Hong Kong University of Science and Technology

CENG 511 Lecture 3

Physical Adsorption

Texture and morphology– specific surface area of catalyst

– pore size

– pore shape

– pore-size distribution (same size or various sizes?)

– pore volume

Pore Size and Shape

Pore Diameter– micropores (< 2 nm)

– mesopores (2 – 50 nm)

– macropores (> 50 nm)

Pore Shape– cylinder

– slit

– ink-bottle

– wedge

Pore Size and Shape

Pore Structure

Silica Carbon Zeolite

Pore Size and Shape

Why is it important?

it dictates the diffusion process through the material.

Configurational diffusion

Surface migration

1000 100 10 1 0.1

10-4

10-8

10-12

10-16

1000 100 10 1 0.1

100

50

0

Ea (kJ/mol)

D (m2/s)

Pore diameter (nm) Pore diameter (nm)

Moleculardiffusion Knudsen

diffusion

Surfacemigration

Pore Size and Shape

Why is it important?

directly affect the selectivity of the catalytic reaction.

Reactant selectivity

+

Product selectivity

CH3OH +

Restricted transition-state selectivity

Pore Size and Shape

Measurement Techniques

1 10 100 1000 10000

Pore diameter (nm)

Micro Meso Macro2 50

N2 capillary condensation

Hg porosimetry

N2 Physisorption

Adsorption and Desorption Isotherms

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p 0

na

d (m

mo

l/g) 1

Adsorption

Desorption


III

nad

p/p0

VI

n ad

p/p0

V

n ad

p/p0

I

n ad

p/p0 p/p

II

nad

0

B

IV

n ad

p/p0

B

N2 Physisorption

Isotherms

Assumptions:

• homogeneous surface

(all adsorption sites energetically identical)

• monolayer adsorption (so no multilayer adsorption)

• no interaction between adsorbed molecules

pK

pKnnn mmad

1

I

n ad

p/p0

Type I Langmuir Adsorption Isotherm

Isotherms

Multilayer adsorption (starting at B)

Common for pore-free materials

p/p

nad

0

B

Type II

Type IV

Similar to II at low p

Pore condensation at high p

n ad

p/p0

B

Isotherms

Type III

Type IV

nad

p/p0

Strong cohesion force between adsorbed molecules, e.g. when water adsorbs on hydrophobic activated carbon

n ad

p/p0

Similar to III at low p

Pore condensation at high p

Physisorption

Surface area measurement

S = nmAmN

monolayercapacity (mol/g)

specific surface area(m2/g)

area occupied by onemolecule (m2/molecule)

Avogadro’s number(molecules/mol)

BET model: SBET

t model: St

Physisorption

Different Adsorbates Used in Physisorption Studies

N2 Physisorption


Langmuir Adsorption?

No:

strong adsorption at low p due to condensation in micropores

at higher p saturation due to finite (micro)pore volume

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

p/p0

nad

(m

mol

/g) 1

a ba b

Z e o l i t e

BET Isotherm

M o d i f i c a t i o n o f L a n g m u i r i s o t h e r m

B o t h m o n o l a y e r a n d m u l t i l a y e r a d s o r p t i o n

L a y e r s o f a d s o r b e d m o l e c u l e s d i v i d e d i n :

– F i r s t l a y e r w i t h h e a t o f a d s o r p t i o n H a d , 1

– S e c o n d a n d s u b s e q u e n t l a y e r s w i t h H a d , 2 = H c o n d

B E T i s o t h e r m :

B E T e q u a t i o n d o e s n o t f i t e n t i r e a d s o r p t i o n i s o t h e r m

– d i f f e r e n t m e c h a n i s m s p l a y a r o l e a t l o w a n d a t h i g h p

0mm

0ad

11

p

p

Cn

C

Cnppn

p

RT

HHC condadexp

r e a l i t y m o d e l 5

4 3

2 1

0

...321 210mad nni

1-nn1-n1

0

nn1-n1

0101

0

111

00

pKpk

kkpk

pKpk

kkpk

d

and

na

d

ada

1 s t l a y e r

n t h l a y e r

F o r e v e r y l a y e rL a n g m u i r m o d e l

A s s u m e

RT

H

RT

H

RT

H

KKK

KK

condn

ads

ee

e

0,n0,nn

0,11

0

0

0m

ad

111pp

C

pp

pp

C

n

nRT

HH

Ccondads

e

w i t h

BET Isotherm

BET IsothermNonporous Silica and Alumina

p/p0

n ad/

n m

(B) (A)

Low p/p0:

• filling of micropores

• favoured adsorption at most reactive sites (heterogeneity)

High p/p0:

• capillary condensation

Range 0.05 < p/p0 < 0.3 is used to determine SBET

BET equation

Pore Size and Surface Area

Material Mean dp (nm) SBET (m2/g)

Catalyst supports

Silica gel 10 200

6 400

4 800

-Al2O3 10 150

5 500

Zeolite 0.6-2 400-800

Activated carbon 2 700-1200

TiO2 400-800 2-50

Aerosil SiO2 - 50-200

Catalysts

MeOH synthesis (Cu/ZnO/Al2O3) 20 80

NH3 synthesis (Fe/Al2O3/K2O) 100 10

Reforming (Pt/Re/Al2O3) 5 250

Epoxidation (Ag/-Al2O3) 200 0.5

Pore Size DistributionKelvin Equation

Pore Size DistributionKelvin Equation

Cylindrical pore

Ink-bottle pore

Pore with shape of interstice between close-packed particles

Adsorbed layertdpdm

Kelvin Equation

m0

12ln

rRT

V

p

p L

micro meso macro

VL = 34.6810 -6 m 3/mol

= 8.88 mN/m

dm (nm)

Rel

ativ

e pr

essu

re p

/p0

0

0.2

0.4

0.6

0.8

1

0.1 1 10 100 1000 10000

Kelvin EquationPore filling Model

Cylindrical Pore Channel

Hysteresis Loop

HI

n ad

p/p0

H2

n ad

p/p0

H3

n ad

p/p0

Information on pore shape

Pore Size Distributiont-Method

nm354.0m

ad n

nt

t

nS

NAt

nS

NAnS

ad6t

m9ad

t

mmt

1073.5

10354.0

nad

t

Proportional to St

Note:

nad is experimental result

t is calculated from correlation t versus p

Kelvin Equationt-Method

BET

– only valid in small pressure interval

– interpretation not very easy

thickness (t) of adsorbed layer can be calculated

plot of t versus p for non-porous materials is the same (has beenchecked experimentally)

t-plot helps in interpretation

0.354 nm

Kelvin EquationShape of t-plots

nm354.0m

ad n

nt

t

n a d

t

n a d

t

n a d

N o n - p o r o u s M i c r o p o r o u sM i c r o - a n d

m e s o p o r o u s

S t

S m e s o p o r e s

p

n a d

A d s o r p t i o n i s o t h e r m

t = f ( p )

Kelvin EquationInterpretation of t-Plot

-alumina

0

2

4

6

8

10

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

na

d (m

mol

/g)

St,micro= 0 m2/g

V t,micro = 0 ml/g

mesopores

macropores

St,micro = 0 m2/g

Vt,micro = 0 ml/g

St = 200 m2/g

Kelvin EquationPore Size Distribution

-alumina

0.0

0.1

0.2

0.3

0.4

0.5

1 10 100 1000

dp (nm)

dV/d

d (m

l/g/n

m)

r = t + 2V

RTIn P0

P

Mercury PorosimetryPore Size Distribution

Hg does not wet surfaces; pressure is needed to force intrusion

From a force balance:

(d in nm, p in bar)

Convenient method for determining pore volume versus poresize

pd

14860p

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000p (MPa)

V (

ml/g

)

Mercury PorosimetryPore Size Distribution

-alumina

N2 Physisorption versus Hg Porosimetry

Adsorbent SHg SBET

m2/g m2/g deg

Iron Oxide 14.3 13.3 130

Tungsten Oxide 0.11 0.10 130

Anatase 15.1 10.3 130

Hydroxy Apatite 55.2 55.0 130

Carbon Black (Spheron-6) 107.8 110.0 130

0.5 % Ru/-Al2O3 237.0 229.0 140

0.5 % Pd/-Al2O3 115.0 112.0 140

TiO2 Powder 31.0 25.0 140

Sintered Silica Pellets 20.5 5.0 140

Zeolite H-ZSM-5 39.0 375.0 140

Norit Active Carbon R1 Extra 112.0 915.0 140

• Hg cannot penetrate small (micro)pores, N2 can

• Uncertainty of contact angle and surface tension values

• Cracking or deforming of samples

Texture Data on Common Catalysts

N2-physisorption Hg-porosimetry

SBET St Vp dp SHg Vp dp

m2/g m2/g ml/g nm m2/g ml/g nm

Wide Pore Silica 78 52 0.91 47 80 0.92 54

-Alumina 196 202 0.49 10 163 0.49 10

-Alumina 9 8 0.12 112 12 0.48 150

Active Carbon 1057a 28 0.51 2 0.6 0.46 106

Raney Ni 76 - 0.14 5.80 - - -

ZSM-5 345 344 0.19 0.58 11 1.1 820b

a p/p0 range of 0.01-0.1 was used in the calculation.b intraparticle voids.

N2 Adsorption Isotherms & Pore Volume Distributions

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g) 1

wide-pore silica -alumina

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g) 1

0.00

0.02

0.04

0.06

0.08

0.10

1 10 100 1000d pore (nm)

dV/d

d (

ml/

g/nm

)

0.0

0.1

0.2

0.3

0.4

0.5

1 10 100 1000d pore (nm)

dV/d

d (

ml/

g/nm

)

N2 Adsorption Isotherms & Pore Volume DistributionsN2 Adsorption Isotherms & Pore Volume Distributions


-alumina activated carbon

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g)

1

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g) 1

0.000

0.002

0.004

0.006

0.008

0.010

1 10 100 1000d pore (nm)

dV/d

d (

ml/

g/nm

)

0.0

0.1

0.2

0.3

0.4

0.5

1 10 100 1000d pore (nm)

dV/d

d (

ml/

g/nm

)} Tensile strength effect

Raney Ni ZSM-5

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g) 1

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1p/p

0

nad

(m

mol

/g) 1

0.00

0.02

0.04

0.06

0.08

0.10

1 10 100 1000d pore (nm)

dV/d

d (

ml/

g/nm

)

0

2

4

6

8

10

0.0 0.5 1.0 1.5 2.0d pore (nm)

dV/d

d (

ml/

g/nm

)


wide-pore silica -alumina

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000p (MPa)

V (

ml/

g)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000

p (MPa)

V (

ml/

g)

0

0.02

0.04

0.06

0.08

1 10 100 1000 10000

d pore (nm)

dV/d

d (

ml/

g/nm

)

0.0

0.1

0.2

0.3

0.4

0.5

1 10 100 1000 10000d pore (nm)

dV/d

d (

ml/

g/nm

)

Hg Intrusion Curves & Pore Volume DistributionsHg Intrusion Curves & Pore Volume Distributions



0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000p (MPa)

V (

ml/

g)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000p (MPa)

V (

ml/

g)

0.000

0.001

0.002

0.003

0.004

0.005

1 10 100 1000 10000d pore (nm)

dV/d

d (

ml/

g/nm

)

0.000

0.002

0.004

0.006

0.008

0.010

1 10 100 1000 10000d pore (nm)

dV/d

d (

ml/

g/nm

)

Raney Ni ZSM-5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000

p (MPa)

V (

ml/

g)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100 1000p (MPa)

V (

ml/

g)

0.00

0.02

0.04

0.06

0.08

0.10

1 10 100 1000 10000

d pore (nm)

dV/d

d (

ml/

g/nm

)

0

0.001

0.002

0.003

0.004

0.005

1 10 100 1000 10000 100000d pore (nm)

dV/d

d (

ml/

g/nm

)


BET- & t-plotsBET- & t-plotswide-pore silica -alumina

0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30

p/p 0

p/[

nad

(p0 -p

)] (

g/m

mol

)

S BET = 78 m2/g

C = 146

0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30p/p 0

p/[

nad

(p0 -p

)] (

g/m

mol

)

S BET = 196 m2/g

C = 97

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

nad

(mm

ol/g

)

S t,micro=28 m2/g

V t,micro = 0.013 ml/g

0

2

4

6

8

10

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

nad

(mm

ol/g

)

S t,micro= 0 m2/g

V t,micro = 0 ml/g


0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30p/p

0

p/[

nad

(p0 -p

)] (

g/m

mol

)

S BET = 9.3 m2/g

C = 142

0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30

p/p0

p/[

nad

(p0 -p

)] (g

/mm

ol)

SBET = 1057 m2/gC = 1057

p/p0 = 0.01 - 0.1

0.00

0.05

0.10

0.15

0.20

0.25

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

nad

(m

mol

/g)

S t, micro= 1.4 m2/g

V t,mcro = 0.001 ml/g

0

5

10

15

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

nad

(m

mol

/g)

S t,micro = 856 m2/g

V t,micro = 0.42 ml/g

BET- & t-plotsBET- & t-plots

Raney Ni ZSM-5

0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30

p/p 0

p/[

nad

(p0 -p

)] (

g/m

mol

)

S BET = 76 m2/g

C = 46

0.0

0.1

0.2

0.3

0.4

0.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30p/p

0

p/[

nad

(p0 -p

)] (

g/m

mol

)

SBET = 345 m2/g

C = -245

p/p0 : 0.01 -0.1

0

1

2

3

4

5

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

n ad

(mm

ol/g

)

St,micro = 0 m2/g

Vt,micro = 0 ml/g

0

2

4

6

0.0 0.2 0.4 0.6 0.8 1.0 1.2t ( nm)

n ad

(mm

ol/g

)

St ,micro= 344 m2/g

Vt ,micro = 0.18 ml/g

BET- & t-plotsBET- & t-plots

ChemisorptionSurface Characterization

• Specific surface area of phases

• Types of active sites

• Number of active sites

• Reactivity of active sites

• Stability of active sites

ChemisorptionMetal Dispersion

Dn

n S

T

Dispersion:

Chemisorption: titration of surface sites

ns = number of surface atoms

nT = total number of atoms

p

nads

number of moles in monolayer

Stoichiometry ??

ns

Adsorption Mode

O

CC

O

C

O

C

O

C

OC O

a. b. c. d. e.

a. linear or terminal (X = 1)

b. bridged (X = 0.5)

c. bridged (X = 0.67)

d. valley or triple (X = 0.33)

e. dissociative adsorption (X = 0.5)

X = average number ofadsorbed molecules peractive site

Adsorption Stoichiometry

Metal N2O/Me H/Me CO/Me

Pt 1 1

Cu 0.5 poor H2 dissociationcatalyst

1

Ni 0.67 1 carbonyl formation!

Rh d > 2 nmRh d < 2 nm

12

1

Particle Size and Dispersion

dV

S DVS 61A

A

Dn

n S

T

D most fundamental parameter

dVS most convenient for measuring directly (XRD, EM)

dVS(nm)

D

Ni

Pt

15

10

5

00.0 0.5 1.0

Supported Metal Particles

a.

c.

b.

d.

poisoned part ofsurface

Spherical

Crystallite

Hemispherical

Complete wetting

Number of Surface Atoms

Metalpart. size ca 5 nm33% (111) plane33% (100) plane33% (110) plane

(atoms.nm-2)

part. size ca 15 nm70% (111) plane25% (100) plane5% (110) plane

(atoms.nm-2)

Co 15.1 -

Ni 15.4 17.5

Pt 12.5 14.2

Pd 12.7 14.5

Ru 16.3 -

Rh 13.3 15.5

Cu 14.7 16.7

Pulse Chemisorption

Catalyst Detector

CO

Pulse Response

Example: Ptsurface + CO Pt-CO

Difference in total peak area nsurface

Pulse Chemisorption

0.0

1.0

0 1Time of analysis

Det

ecto

r si

gnal

CO chemisorption on reduced 5wt% Pt/Al2O3

TCD signals after CO pulses

0.00

0.02

0.04

0.06

0.08

0 0.5 1 1.5

Pulsed volume (ml)n

ad (

mm

ol/g

)

S Pt = 3 m2/g

D Pt = 24 %

SPt = 3 m2/g

DPt = 24 %

CO chemisorption on reduced 5wt% Pt/Al2O3

Cumulative amount of chemisorbed CO

Monolayer capacity: 0.06 mmol / g Pt

On-line Thermoconductivity Detector

Step ChemisorptionOn-line Mass Spectrometer

Example: 2 Cu(s) + N2O Cu2O(s) + N2

CatalystMass

Spectrometer

t

N2ON2O

N2

Step Response

Temperature Programmed DesorptionAdsorption Site Differentiation

NH3 desorption from HZSM-5

Weak acid sites

Strong acid sites

Temperature Programmed DesorptionAdsorption Energetics

After ammonia saturation the sample is degassed at 120 °C for 60 minutes

2352

89

2408

66

2196

21

2050

24

150Time ( min )

0 50 100 150

300

Sig

na

l (m

V/g

)

0

100

200

300

600

Te

mp

era

ture

( °

C )

0

200

400

600

Heating Rate of 5, 10, 15 and 20 °C/min

Temperature Programmed DesorptionAdsorption Energetics

Desorption Energy Calculation

9.8

10

10.2

10.4

10.6

10.8

11

11.2

0.0015 0.00155 0.0016 0.00165 0.0017 0.00175 0.0018 0.00185 0.0019

1/Tp (K)

Ln

(Tp

2/b

eta)

Beta (K/min) Tp °C Tp K Tp2 1/Tp K Ln(Tp2/beta) 5 266 539 290521 0.0018552 10.9699

10 311 584 341056 0.0017123 10.4372 15 356 629 395641 0.0015898 10.1802 20 382 655 429025 0.0015267 9.9735

Beta = heating rate [K / min]Tp = maximum desorption peak temperatureEd = Desorption energy [Kj / mole]A = Arrhenius factorR = 8.314451 [J / mol K]

12.49A factor

24.51Ed (kJ/mole)

5.4639Intercept

2948.07Slope

Temperature Programmed Reduction

– characterisation of oxidic catalysts and other reducible catalysts

– qualitative information on oxidation state

– quantitative kinetic data

– optimisation of catalyst pretreatment

Reduction of oxidic species:

Study of coke deposits:

Reduction of sulphides:

MO + H2 M + H2O

coke + H2 hydrocarbons + H2O

MS + H2 M + H2S

Reduction of oxidic species:

Study of coke deposits:

Reduction of sulphides:

MO + H2 M + H2O

coke + H2 hydrocarbons + H2O

MS + H2 M + H2S

Temperature Programmed ReductionFe2O3

7.0 mg

15.9 mg

8.2 mg

3.6 mg

H2/Ar saturatedwith 3% H2O

dry H2/Ar

500 600 700

Temperature (K)

d

c

b

a


0.2 K/min3.6 mg

0.5 K/min2.8 mg

1.0 K/min1.8 mg

2.0 K/min0.91 mg

5.0 K/min0.19 mg

10.0 K/min0.08 mg

500 600 700

Temperature (K)

f

c

b

a

d

e

Dry H2/Ar

0.2 K/min7.0 mg

0.5 K/min2.6 mg

1.0 K/min1.5 mg

2.0 K/min0.90 mg

5.0 K/min0.33 mg

10.0 K/min0.17 mg

500 600 700 800

Temperature (K)

f

c

b

a

d

e

Wet H2/Ar (3% H2O)


ab c(K-1 s-1)

-15

-16

-17

-18

-19

2max

βln

T

max

1T

(10-4 K-1)

12 13 14 15 16 17 18

wet seriesmain peak

wet serieslow T peak

dry seriesmain peak

Ea = 111 kJ/mol


Kinetic Models for ReductionModel f() g()nth Order

Random nucleationUnimolecular decay law

Phase boundary controlled reaction(contracting area)

Phase boundary controlled reaction(controlled volume)

Two dimensional growth of nuclei(Avrami-Erofeev)

Three dimensional growth of nuclei(Avrami-Erofeev)

One dimensional diffusionParabolic law

Two dimensional diffusion

Three dimensional diffusion(Jander)

Three dimensional diffusion(Ginstling-Brounshtein)

(1-)n

(1-)

(1-)1/2

(1-)2/3

2(1-)[-ln(1-)]1/2

3(1-)[-ln(1-)]2/3

1/2

-1/ln(1-)

[3(1-)2/3]/ [2(1-(1-)1/3)]

3/[2((1-)-1/3 -1)]

(1-(1-)1-n)/(1-n)

-ln(1-)

2(1-(1-)1/2)

3(1-(1-)1/3)

[-ln(1-)]1/2

[-ln(1-)]1/3

2

(1-)ln(1-) +

[1-(1-)1/3]2

1-2/3 - (1-)2/3

Infrared Spectroscopy

Applications:

Catalyst characterisation– direct measurement of catalyst IR spectrum– measurement of interaction with “probe” molecules:

• NH3, pyridine: acidity• CO, NO: nature of active sites (e.g. Pt on alumina)

Mechanistic studies– adsorbed reaction intermediates– deactivation by strongly adsorbing species

Analysis of reactants and products (in situ reactionmonitoring

Electromagnetic Spectrum

UV Visible IR

4000 - 400 cm-1

Infrared SpectroscopyReactor Cell

DRIFTS

Transmittance

Analysis of Catalyst PreparationSurface Hydroxyl Groups

NH4ReO4

Alumina

Dry impregnation

Drying 383 K, 16 h

Calcination 323 K, 2 h

Re2O7/

Alumina

Abs

orba

nce

3900 3800 3700 3600 3500

0%

3%

6%

12%

18%

Re2O7loading

Basic

Neutral

AcidicAl

OH

AlO

Al

Al

H

Intensitydecreases

Re-loadingincreases

Re

OO O

O

A l

Re

OO O

O

A l A l

Re

O HOO

O

A l3+

–

+

a b cR eO 4 on Lew is s ite

no t ac tive

B as ic -O Hsubstitu ted by R eO 4

s ligh tly ac tive

A c id ic -O Hsubstitu ted by R eO 4

active

Analysis of Catalyst Preparation

Alumina contains Lewis and Brönsted sites

OH-spectrum different acid sites

Impregnation

– OH + HOReO3 -OReO3 + H2O

– Al3+ + HOReO3 coordination complex

Low-loading Re/Al not effective

IRS gives detailed picture of surface

IR Probe MoleculeAcidity Measurement

N

Pyridine adsorbs on acid sites

Spectrum changes

N

Lewis acid

N

Brönsted acid

Different IR Spectra

F/Al2O3 very active in acid-catalysed reactions

Al2O3 F/Al2O3

F/Al2O3

HF

F-salt

Structure of F/Al2O3 ???

Acid sites? Bronsted, Lewis???, How many??

IR Probe MoleculeAcidity Measurement


no reaction with HCl with BH3

1438 vs 1487 vs 1458 s1482 m 1536 s 1488 s1585 vs 1610 m 1587 m1601 m 1636 m 1621 vsvs: very strong; s: strong; m: medium

N

B

ClClCl

N

H+ Cl-1700 1600 1500 1400

(cm-1)

B

B

L L


Background spectrum F/Al2O3

After addition of H2O at 330 Kand evacuation at 330 K

After adsorption of pyridine at 330 K

Lewis site Brönsted siteH2O

Wavenumber (cm-1)1300 1500 1700

Transm

ission

L1452

L1619

B1639

B1490

L1497

L1579

B1542

b

c

a

In-Situ Reaction Study

UV / min

0

26

46

66

86

106

126

146

166

186

UVair 60

Figure 2a TCE on P-11t on 21/3/01

800 1200 1600 2000 2400

Wavenumber / (cm-1)

2345

2365

950 1263850

1413

1589

2400 2800 3200 3600 4000

Wavenumber / (cm-1)

1415

1610

1649

1747

1787

3105

1234

1568

1602

3452

32982978

3751 3868

TCE Photocatalytic Oxidation

In-Situ Reaction StudyPCO of Ethylene

0

0.25

0.5

0.75

1

0 50 100 150 200

Irradiation time / (min)

I95

0(=

C-H

)

P-11t

P-11h(new)

P-11h(old)

Fig. 6a

0 50 100 150 200


CO2

H2O

Fig. 6c

0 50 100 150 200


Fig. 6c

H2O

CO2HCHO

In-Situ Reaction StudyPCO of 1,1-DCE

0 50 100 150 200


CO2HCHO

H2O

Cl2COO

Fig. 4b

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200

Irradiation time/ (min)

I10

95

(-C

Cl)

P-11t

P-11h

Fig. 4a

0 50 100 150 200


H2O

CO2

Fig. 4c

Cl2COO

HCHO

In-Situ Reaction StudyPCO of cis-1,2-DCE

0 50 100 150 200


H2OHCHO

CO2

Cl2CCO

Fig. 2c

0 50 100 150 200

Irradiaition time /(min)

H2OHCHO

CO2

Cl2CCOO

Fig. 2b

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200Irradiation time / (min)

I 86

4(C

lC

-H

)

P-11t

P-11hFig. 2a

In-Situ Reaction StudyPCO of trans-1,2-DCE

0

0.25

0.5

0.75

1

0 50 100 150 200


I89

8(C

lC

-H

)

Fig. 3a

0 50 100 150 200


CO2

Cl2COO

H2OHCHO

Fig. 3b

0 50 100 150 200

Irradiaiton time / (min)

Fig. 3c

Cl2COO

CO2

HCHOH2O

H2O

HCHO

In-Situ Reaction StudyPCO of TCE

0 50 100 150 200


CO2

Cl2CCOO

HCHOH2O

Fig. 1b

0 50 100 150 200


CO2

H2O

Fig. 1c

HCHOCl2COO

0

0.25

0.5

0.75

1

0 50 100 150 200


I94

7(C

lC

-H

)

P-11t

P-11h

Fig. 1a

In-Situ Reaction StudyPCO of Tetrachloroethylene

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200


I92

1?(H

-C

Cl)

P-11t

P-11h

Fig. 5a

0 50 100 150 200


CO2

H2O

HCHO

Fig. 5c

0 50 100 150 200


Fig. 4b

CO2HCHO

H2O

Documents

Adsorption and Catalysis Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology CENG 511 Lecture 3