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Ni-phyllosilicate structure derived Ni-SiO2-MgO catalysts for bi-
reforming applications: acidity, basicity and thermal stability.
J. Ashok, Z. Bian, Z. Wang and S.Kawi*
Experimental
The surface area and total pore volume of the freshly calcined, reduced and spent catalysts were
measured by N2 physical adsorption at −196 °C in an ASAP 2020 instrument. Prior to N2
physical adsorption, all the catalysts were degassed under vacuum at 300°C for 3 h. The specific
surface area was calculated by applying the Brunauer-Emmett-Teller (BET) method. HRTEM
system JEOL JEM-2100F was used to analyze surface morphology of calcined, reduced and
spent catalysts. The catalyst sample was ultrasonically dispersed in ethanol and spread over
perforated copper grids. The X-ray diffraction (XRD) patterns of fresh, reduced and spent
catalysts were measured on a Shimadzu XRD-6000 diffractometer using Cu Kα radiation. The
catalyst was scanned for 2θ range between 10° to 60° at a ramp rate of 2°/min.
Ni and Mg compositions of the catalysts were measured with Thermal Scientific iCAP 6000
ICP-OES Analyser. 15mg powder was dissolved in a mixture of 0.5 ml HF (48%), 2mL HNO3
(65%) and 40mL DI water aided by ultrasonic treatment. Ni and Mg ICP standard solution
diluted to appropriate concentrations was used to prepare the calibration curve.
Electronic Supplementary Material (ESI) for Catalysis Science & Technology.This journal is © The Royal Society of Chemistry 2018
The H2 Temperature-programmed reduction (TPR) and CO2-Temperature-programmed
reduction (TPD) experiments was conducted using Thermo Scientific TPDRO 1100 series
system (with TCD detector). For H2-TPR, 0.03 g of catalyst sample was outgassed in N2 gas for
1 h at 300°C to remove any moisture and then cooled to room temperature. Then, 5% H2/N2 gas
was introduced to the catalyst while the temperature of the furnace was increased to 950°C (ramp
rate of 10°C/min). For CO2-TPD, about 100 mg of catalyst sample was reduced at 750°C for 1 h
under H2 gas (30 mL/min). After that, the samples were cooled to 50°C where CO2 adsorption
was carried out for 30 min. Then the samples were purged in He gas for 30 min. Desorption of
CO2 took place while heating the sample from 50 to 1000°C (ramp rate of 10°C/min).
The surface Ni metal content and dispersion was calculated by using N2O titration
method. Prior to N2O titration at 70 °C, the sample (W = 30 mg) was reduced at 750 °C
for 1 h under H2 gas, and then cooled to 70 °C in helium gas flow of 30 mL/min. At this
temperature, the N2O decomposition was carried out by introducing several pulses of N2O
gas using 99.99% N2O with a loop volume of 344 µL. This was followed by TPR with
temperatures up to 750 °C performed in the TPDRO 1100 series system. The amount of
the oxidized Ni surface atoms by N2O decomposition was estimated by measuring the H2
consumed during TPR analysis, in accordance to Eq’s below.
Ni0 + N2O → NiO + N2
NiO + H2 → Ni0 + H2O
The reduced and spent catalysts surface analysis was performed using X-ray
photoelectron spectroscopy (XPS) from a KRATOS AXIS Hsi 165 equipped with Mg-Kα source
(1253.6 eV). Prior to the analysis for reduced catalysts, the catalyst was reduced at 750ºC under
H2 for 1 h. For spent catalyst, the catalysts were used as collected from reforming reactor. Then
the sample was mounted on the standard sample stub using double-sided adhesive tapes. All
binding energies were referenced to C 1s hydrocarbon peak at 284.6 eV. Shimadzu DTG-60
thermo gravimetric analyzer was used to analyse total amount and nature of deposited carbon on
the spent catalysts. Around 10 mg of spent catalyst was used in each DTA/TGA experiment and
heated in air to 1000°C with a heating rate of 10°C/min.
Table S1. The amount of metal precursors taken for synthesizing Ni-SiO2-Mg[x]
catalysts, nominal and actual metal contents present in the calcined catalysts
Amount of metal precursor[a]Catalyst
Ni nitrate
(grams)
SiO2
(grams)
Mg nitrate
(grams)
Nominal wt%
composition
(Ni:SiO2:Mg)
Actual wt%
composition
(Ni:SiO2:MgO)
Ni-SiO2 1.49 3.4 -- 15:85:0 13.1±0.5:--:--
Ni-SiO2-MgO[25] 1.49 2.4 5.27 15:60:25 13.8±0.6:--:22.2±1
Ni-SiO2-MgO[40] 1.49 1.8 8.44 15:45:40 11.50.4:--:35.60.6
Ni-SiO2-MgO[55] 1.49 1.2 11.60 15:30:55 12.20.6:--:52.60.8
Ni-MgO[85] 1.49 -- 17.93 15:00:85 9.40.5:--: 611
[a] calculated to prepare 2g of the calcined catalyst; [b] determined using ICP-OES analyzer.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
(e)(d)
(c)
(b)
Qua
ntity
ads
orbe
d/de
sorb
ed(c
m3 /g
)
Relative pressure/(P/Po)
100
(a)
Figure S1. N2 adsorption-desorption isotherms of calcined (a) Ni-MgO, (b) Ni-SiO2-MgO[55],
(c) Ni-SiO2-MgO[40], (d) Ni-SiO2-MgO[25] and (e) Ni-SiO2 samples.
0 3 6 9 12 15 180
20
40
60
80M
etha
ne c
onve
rsio
n/(%
)
Time on stream/(h)
Ni-SiO2
Ni-SiO2-MgO[25] Ni-SiO2-MgO[40] Ni-SiO2-MgO[55] Ni-MgO
(A)
0 2 4 6 8 10 12 14 16 18 200
20
40
60
80
(B)
CO2 c
onve
rsio
n/(%
)
Time on stream/(h)
Ni-SiO2
Ni-SiO2-MgO[25] Ni-SiO2-MgO[40] Ni-SiO2-MgO[55] Ni-MgO
Figure S2. Time dependant (A) CH4 conversion and (B) CO2 conversion over Ni-SiO2-MgO[x]
catalysts during bi-reforming of methane reaction. Conditions: W = 0.01 g; CH4 = 20 mL/min;
CO2 = 10 mL/min; Steam = 20 mL/min; He = 50 mL/min; Reduction temperature = 750°C/1 h;
and Reaction temperature = 750°C.
500 550 600 650 700 750 800 850 900-25
0
25
50
75
100
CH4 conversion H2O conversion CO2 conversion CH4
H2O CO2
CO H2
Temperature/0C
CH4/C
O2/H
2O c
onve
rsio
n(%
)
solid
open
0
10
20
30
40
50
60 Products distribution/(molar flow rate)
Figure S3. Calculated thermodynamic equilibrium conversion for bi-reforming of
methane reaction. Condition: CH4 = 20mL/min, H2O = 20 mL/min, CO2 = 10mL/min and He =
50mL/min.
500 550 600 650 700 750 800 850 900-25
0
25
50
75
100
CH4/C
O2 c
onve
rsio
n/(%
)
Temperature/0C
CH4 (equilibrium) CO2 (equilibrium) CH4 (experimental) CO2 (experimental)
Figure S4. Actual and calculated thermodynamic equilibrium CH4 and CO2 conversions
during bi-reforming of methane reaction. Condition: CH4 = 20mL/min, CO2 = 10mL/min, H2O =
20mL/min and He = 50mL/min.
0 5 10 15 20 25 30 35 40 45 500
20
40
60
80
100 CH4 (7500C); CH4 (7000C); CH4 (6500C) CO2 (7500C; CO2 (7000C); CO2 (6500C) H2/CO (7500C); H2/CO (7000C); H2/CO (6500C)
Time on stream/(h)
CH4/C
O2 c
onve
rsio
n/(%
)
0.8
1.2
1.6
2.0
2.4H
2 /CO
Figure S5. Bi-reforming of methane over Ni-SiO2-MgO[55] at various reaction temperatures
Figure S5 depicts the Bi-reforming of methane (BRM) performance over Ni-SiO2-MgO[55] at
reaction temperature between 650 and 750°C. The result shows that both CH4 and CO2
conversions are decreased with decrease in reaction temperature. The H2/CO values at 650°C is
slightly higher than other reaction temperatures, which is possibly due to better water-gas-shift
reaction at lower reaction temperature.
0 5 10 15 20 25 30 35 40 45 500
20
40
60
80
100
CO2
Time on stream/(h)
CH4/C
O2 c
onve
rsio
n/(%
)(a)
CH4
Condition: CH4:CO2:H2O = 2:1:2
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
H2 /CO
0 5 10 15 20 25 30 35 40 45 500
20
40
60
80
100
Time on steam/(h)
CH4/C
O2 c
onve
rsio
n/(%
)
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
Condition: CH4:CO2:H2O = 2:1:1.5
H2 /CO
CH4
CO2
(b)
0 5 10 15 20 25 30 35 40 45 500
20
40
60
80
100
Condition: CH4:CO2:H2O = 2:1:1
Time on stream/(%)
CH4/C
O2 c
onve
rsio
n/(%
)
CO2
CH4
(c)
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
H2 /CO
Figure S6. Bi-reforming of methane over Ni-SiO2-MgO[55] catalyst at various CH4/H2O ratios.
According to Figure S6 the methane conversions were slightly decreased and CO2 conversion
was increased with decreasing steam amount in the feed is observed. This result shows that the
H2/CO values can easily be tuned by changing the amount of steam in the feed.
100 200 300 400 500 600 700 800 900-150
-100
-50
0
50
100
150
750oC 700oC 650oC CH4:H2O = 2:1.5 CH4:H2O = 2:1
Temperature/oC
DTA,
rate
of w
t. lo
ss (d
m/d
T)
50
60
70
80
90
100
110
TGA, weight loss (%
)
Figure S7. DT/TGA profiles for spent Ni-SiO2-MgO[55] catalyst at various reaction conditions.
The carbon formation during reforming reaction is observed at reaction temperature of 650°C
and at low steam condition. The carbon formation is negligible for almost all other reaction
conditions.
1400 1450 1500 1550 1600 1650 1700
0.0
0.1
0.2
0.3
0.4
0.5
LAS
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
LAS
(A) - Ni/SiO2
1400 1450 1500 1550 1600 1650 1700
0.0
0.1
0.2
0.3
0.4
0.5
LAS/BAS BAS
LAS
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
(B) - Ni-SiO2-MgO[25]
LAS
1400 1450 1500 1550 1600 1650 17000.0
0.1
0.2
0.3
0.4
0.5
LAS
BAS
LAS/BAS
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
LAS
(C) - Ni-SiO2-MgO[40]
1400 1450 1500 1550 1600 1650 17000.0
0.2
0.4
0.6
0.8
BASLAS
LAS/BAS
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
LAS
(D) - Ni-SiO2-MgO[55]
1400 1450 1500 1550 1600 1650 17000.0
0.1
0.2
0.3
0.4
0.5
0.6
BASLAS
LAS/BASInte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
LAS
(E) - Ni-MgO
Figure S8. Pyridine-DRIFTS over reduced Ni-SiO2-MgO[x] catalysts. The pyridine is adsorbed
at 150C and desorbed between 150 and 400C in the presence of He gas.
3500 3550 3600 3650 3700 3750 3800-0.1
0.0
0.1
0.2
0.3
0.4
0.5In
tens
ity/a
.u.
wavenumber/cm-1
150 200 250 300 350 400
(A) - Ni-SiO2
(I)-OH(B)-OH
3500 3550 3600 3650 3700 3750 3800-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
(I)-OH(B)-OH
(T)-OH(B) - Ni-SiO2-MgO[25]
3500 3550 3600 3650 3700 3750 3800
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
(B)-OH
(I)-OH
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
(T)-OH
(C) - Ni-SiO2-MgO[40]
3500 3550 3600 3650 3700 3750 3800
0.0
0.3
0.6
Inte
nsity
/a.u
.
wavenumber/cm-1
150 200 250 300 350 400
(D) - Ni-SiO2-MgO[55]
3500 3550 3600 3650 3700 3750 3800
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7In
tens
ity/a
.u.
wavenumber/cm-1
150 200 250 300 350 400
(E) - Ni-MgO
Figure S9. Hydroxyls region of Pyridine-DRIFTS over reduced Ni-SiO2-MgO[x] catalysts. The
pyridine is adsorbed at 150C and desorbed between 150 and 400C in the presence of He gas.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Qua
ntity
ads
orbe
d/de
sorb
ed(c
m3 /g
)
Relative pressure/(P/Po)
100
(a)
(b)
(c)
(d)
(e)
(A)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
(e)
(d)
(c)
(b)
Qua
ntity
ads
orbe
d/de
sorb
ed(c
m3 /g
)
Relative pressure/(P/Po)
100
(a)
(B)
Figure S10. N2 adsorption-desorption isotherms of (A) reduced and (B) spent (a) Ni-MgO, (b)
Ni-SiO2-MgO[55], (c) Ni-SiO2-MgO[40], (d) Ni-SiO2-MgO[25] and (e) Ni-SiO2 samples.