Doped CeO_2 with a low specific surface area is thermochemically cycled between MO_2 and MO_(2-δ) using H_2O and CO_2 as oxidants. The system rapidly and selectively produces syngas in the absence of a metal catalyst, and CH_4 in the presence of Ni. The Ni catalyst, which permits intermediate C to form on its surface, is proposed to shift the product from syngas to CH_4

Chueh, William C.

Haile, Sossina M.

Caltech Authors - Main

 
 
 
 
 
 
 
 
 
 
 
 
 
Supporting Information 
 
© Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2009 
 
 
 
1 
Ceria as a Thermochemical Reaction Medium for Selectively Generating 
Syngas or Methane from H2O & CO2 
 
William C. Chueh, Sossina M. Haile 
 
Supporting Information 
 
                 
2 
0 1 2 3 4 5
0
1
2
3
4
5
6
600
800
1000
1200
1400
1600
 
Te
m
pe
ra
tu
re
 (°
 C
)
O
2 R
at
e 
(s
cc
m
 g
-1
   
  )
t (min)
C
eO
2
 
 
Fig. S1. Oxygen release rate from fully oxidized CeO2 upon rapid heating from 700 to 1500 °C 
in an infrared furnace under flowing 11 ppm O2 in N2 supplied at a flow rate of  
1470 sccm g-1CeO2. Oxygen evolution was rapid and limited by the ramp rate of the furnace. 
Integrating the rate curve gives an oxygen nonstoichiometry of 0.06.  
The sample was fabricated in the same way as indicated in the Experimental section. An alumina 
tube (9.5 mm inner diameter) served as the reactor with the exhaust gas connected to a Pfeiffer 
Thermostar quadrupole mass spectrometer.  
3 
Ni-SDC 
Temperature 
(ºC) 
VH2 (mL g-1) VCH4 (mL g-1) VCO (mL g-1) SCH4 (%) X 
400 1.0 ± 0.1 1.1 ± 0.1 0.05 ± 0.01 80 0.8 ± 0.1 
500 3.2 ± 0.3 0.7 ± 0.1 0.28 ± 0.02 46 1.0 ± 0.1 
600 4.3 ± 0.3 0.30 ± 0.02 1.3 ± 0.1 18 1.1 ± 0.1 
700 4.1 ± 0.3 0 1.9 ± 0.2 0.2 0.9 ± 0.1 
Table S1(a). Fuel productivity and extent of reaction data corresponding to Fig. 2(top). 
SDC 
Temperature 
(ºC) 
VH2 (mL g-1) VCH4 (mL g-1) VCO (mL g-1) SCH4 (%) X 
400 4.7 ± 0.4 0 0.36 ± 0.08 0 0.8 ± 0.1 
500 4.5 ± 0.4 0 1.8 ± 0.1 0 1.0 ± 0.1 
600 3.9 ± 0.3 0 1.8 ± 0.1 0 0.9 ± 0.1 
700 4.1 ± 0.3 0 2.0 ± 0.2 0 0.9 ± 0.1 
Table S1(b). Fuel productivity and extent of reaction data corresponding to Fig. 2(bottom) 
V is the total volume of gas produced, SCH4 is the methane selectivity, defined as SCH4 = 
4VCH4/(4VCH4+VH2+VCO) and X is the extent of reaction, defined as the ratio of fuel produced to 
the theoretical fuel productivity, as set by the initial oxygen nonstoichiometry.  
4 
0 2 4 6 8 10
0
1
2
3
4
5
SDC
SD
C
700 ºC, pH2O = 0.064 atm, FRtot = 380 sccm g
-1
R
at
e 
(s
cc
m
 g
-1
   
)
 
 
 t (min)
 Cycle 1
 Cycle 31
 Cycle 53
 
Cycle No. VH2 (mL g-1) X 
1 7.6 ± 0.6 1.2 ± 0.1 
31 7.6 ± 0.6 1.2 ± 0.1 
53 7.7 ± 0.6 1.2 ± 0.1 
 
Fig. S2 / Table S2. H2 production as a function of time, as measured by gas chromatography 
upon exposure of reduced SDC to mildly humidified N2/Ar at the conditions indicated (FRtot is 
the total flow rate). Efficacy of H2O splitting is largely unchanged after 53 redox cycles (other 
cycles at various conditions). V is the total volume of gas produced, SCH4 is the methane 
selectivity, defined as SCH4 = 4VCH4/(4VCH4+VH2+VCO) and X is the extent of reaction, defined as 
the ratio of fuel produced to the theoretical fuel productivity, as set by the initial oxygen 
nonstoichiometry.  
 
5 
0 5 10 15 20
0.0
0.1
0.2
0.3
0.4
0.5
SDC
SD
C
R
at
e 
(s
cc
m
 g
-1
   
)
t (min)
500 ºC, pH2O = 0.064 atm
pCO2 = 0.032 atm, FRtot = 10 sccm g
-1
 
CO
CH4
Cycle 1
Cycle 6
Cycle 11
H2
 
Cycle No. VH2 (mL g-1) VCH4 (mL g-1) VCO (mL g-1) SCH4 (%) X 
1 3.5 ± 0.3 0.74 ± 0.06 0.31 ± 0.02 44 1.0 ± 0.1 
6 3.2 ± 0.3 0.74 ± 0.06 0.28 ± 0.02 46 1.0 ± 0.1 
11 3.4 ± 0.3 0.81 ± 0.07 0.23 ± 0.02 47 1.0 ± 0.1 
 
Fig. S3 / Table S3. Fuel production as a function of time, as measured by gas chromatography, 
upon simultaneous exposure of reduced Ni-SDC to H2O and CO2 (balance Ar/N2) at the 
conditions indicated (FRtot is the total flow rate). Fuel production curves as well as CH4 
selectivity are stable after 11 redox cycles (other cycles at various conditions). V is the total 
volume of gas produced, S is the selectivity, defined as…. and X is the extent of reaction, 
defined as… 
6 
                       
1.0 1.1 1.2 1.3
-0.8
-0.4
0.0
0.4
700 600 500
SD
C
 H2O Splitting, PH2O = 0.064 atm
 CO2 Splitting, PCO2 = 0.032 atm
0.80 ± 0.02 eV
T (ºC)
 
Lo
g 
(r i
ni
t /
 s
cc
m
 g
-1
   
)
1000 T-1 (K-1)
0.52 ± 0.02 eV
 
                         
-2.0 -1.8 -1.6 -1.4 -1.2 -1.0
-0.6
-0.4
-0.2
0.0
0.2
SD
C
 H2O Splitting
 CO2 Splitting
T = 600 ºC
 
0.77 ± 0.02  
Lo
g 
(r i
ni
t /
 s
cc
m
 g
-1
   
)
Log (Pi / atm)
0.54 ± 0.01
 
Fig. S4. Initial production rates of H2 and CO as functions of (a) temperature and (b) reactant 
partial pressures when H2O and CO2 are individually reacted with reduced SDC, respectively. 
The rates shown here correspond to that at t = 0. We take the initial state in all cases to 
correspond to the same value of oxygen nonstoichiometry. 
(a) 
(b) 
7 
The instantaneous reactant conversion rate was kept below 20 % to satisfy the gradient-less 
reactor and isothermal approximations (ΔT < 3 °C) (Fig. S2). To avoid equilibrium limitations in 
the fuel production reactions, reactant flow rates were kept sufficiently high such that the 
2 2
:H O Hp p  and 2 :CO COp p  ratios at the exhaust were always above 9 (for determining reaction 
orders) and above 5 (for determining activation energies).   
8 
                             
0 2 4 6
0
2
4
6
8
SDC
SDC
SD
C
800 ºC, pH2O = 0.064 atm, FRtot = 380 sccm g
-1
t (min)
H
2 R
at
e 
(s
cc
m
 g
-1
   
)
 
 
7.5 ± 0.6 mL g-1
 
 
                             
0 2 4 6 8 10
0
1
2
3
4
5
6
SDC
SD
C
  
t (min)
H
2 R
at
e 
(s
cc
m
 g
-1
   
)
T = 750 ºC, PH2O = 0.023 atm, FRtot = 200 sccm g
-1
 
 SDC
 2 wt% Rh-SDC
 
Fig. S5. (a) H2 production rate as a function of time, as measured by gas chromatography, upon 
exposure of reduced SDC to mildly humidified N2/Ar at the conditions indicated (FRtot is the 
total flow rate). The total quantitiy of hydrogen produced (value indicated) implies an extent of 
reaction X  = 1.2 ± 0.1. (b) Comparison of H2 fuel production curves for SDC with and without 2 
wt% Rh..  
 
 
(a) 
(b) 
9 
0 2 4 6 8 10
0
2
4
SDC
SDC
S
D
C
800 ºC, pCO2 = 0.032 atm, FRtot = 300 sccm g
-1
C
O
 R
at
e 
(s
cc
m
 g
-1
   
)
t (min)
 
 
7.0 ± 0.6 mL g-1
 
Fig. S6 CO production rate as a function of time, as measured by gas chromatography, upon 
reaction of CO2 with reduced SDC at the conditions indicated (FRtot is the total flow rate). No C 
was detected as verified by post situ TPO. Total quantity of CO produced (value indicated) 
implies an extent of reaction of X  = 1.1 ± 0.1. 
10 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                   
 
Fig. S7. Equilibrium compositions calculated at 1 atm for the starting materials indicated 
with
2H O
p = 0.064 atm and 
2CO
p = 0.032 atm.
200 400 600 800
0.00
0.10
0.20
0.30
0.40
0.50
 
M
ol
e
H2
T(ºC)
Starting Materials: 
0.5 mole H2O
10 mole SDC (= 0.05) (a)
200 400 600 800
 
 
 
 
H2
0.5 moles H
2
O
10,000 moles SDC (= 0.05) (b)
0.00
0.05
0.10
0.15
0.20
0.25
M
ol
e
C(gr)
CO
0.25 mole CO2,
10 mole SDC ( = 0.05)
(c)
 
 
C(gr) CO
0.25 moles CO
2
,
10,000 mole SDC (= 0.05)
(d)
200 400 600 800
0.00
0.05
0.10
0.15
0.20
0.25
M
ol
e
T (ºC)
H2
CH4
C(gr) CO
0.25 mole H2O
0.125 mole CO2
10 mole 
SDC (= 0.05)
(e)
200 400 600 800
 
H2
CH4 C(gr) CO
0.25 mole H2O
0.125 mole CO
2
10,000 mole 
SDC (= 0.05)
(f)
11 
                   
0 5 10 15
0.0
0.2
0.4
SDC
S
D
C
R
at
e 
(s
cc
m
 g
-1
   
)
t (min)
 
 
 H2
 CH4
 CO
900 ºC, pH2O = 0.132 atm, pCO2 = 0.066 atm
FRtot = 40 sccm g
-1
S
D
C
Im
pl
ie
d 
R
at
e 
of
 C
(s
) D
ep
os
iti
on
 ( 
m
in
-1
 g
-1
   
)
-4
0
4
 
 
 
Fig. S8. (Top) Implied rate of C(s) deposition that occurs upon reaction of H2O and CO2 with 
reduced 10 wt% Ni-SDC at the conditions indicated; and (bottom) fuel production rates. Solid 
carbon formation rate is calculated by taking the difference between the carbon in the the product 
gases and that in the reactants. Integration of the carbon formation rate curve with time indicates 
zero carbon accumulation (within error).  
 
12 
 
Process Temperatures 
(° C) 
Energy 
 (kJ mol-1 Syngas**) 
Heating oxidized SDC  800 → 1500 1431.7 
Reduction of SDC (oxygen release)  1500 412.2 
Cooling reduced SDC  1500 → 800 -1425.1 
Cooling O2(g) 1500 → 25 -25.3 
Heating H2O(l) & CO2(g) 25 → 800 122.3 
Oxidation of SDC (fuel production) 800 -140.2 
Cooling Excess H2O(g) & CO2(g) 800 → 25 -61.2 
Cooling H2(g) & CO(g) 800 → 25 -23.3 
Total energy input  1966.2 
Net energy output  291.2 
Efficiency  14.8% 
** 1 mole of syngas = 2/3 mole of H2 and 1/3 mole of CO. 
Table S4. Following a methodology reported in the literature (1-2), the cycle efficiency for 
syngas production from H2O and CO2 using thermal energy was calculated as the ratio of the 
energy content of the output fuel to the various energy inputs. The oxygen release and H2O/CO2 
splitting half-cycle temperatures were taken to be 1500 °C and 800 °C, respectively. Ceria was 
assumed to attain a nonstoichiometry, , of 0.05 after the reduction step, and chemical reaction 
was assumed to reach equilibrium.  
13 
Solar absorption efficiency (88.8 %) was determined by assuming a blackbody receiver with a 
solar radiation intensity of 1 kW m-2 and a concentration ratio of 5,000 suns in the solar 
concentrator. Assuming no heat recovery, a total cycle efficiency of 13.2 % is obtained. A 
similar result is obtained if one considers the energy content of the synthesized fuel as the net 
energy output. With 50 % heat recovery, the efficiency increases to 22.9 %. 
Some amount of N2 with low oxygen content will be required to prevent oxidation of ceria and 
the product. The energy cost for N2 separation from air is typically ~ 20 kJ/mol (3).  
 
Supplementary References 
S1. A. Steinfeld, , S. Sanders, R. Palumbo, Energy 1999, 65, 43.  
S2.  C. Perkins, A.W. Weimer, Int. J. Hydrogen Energy 2004, 29, 1587. 
S3.  H-W. Haring in Industrial Gases Processing, 2008.  
 
 


Ceria as a Thermochemical Reaction Medium for Selectively Generating Syngas or Methane from H_2O and CO_2

 
 
 
 
 
 
 
 
 
 
 
 
 
Supporting Information 
 
© Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2009 
 
 
 
1 
Ceria as a Thermochemical Reaction Medium for Selectively Generating 
Syngas or Methane from H2O & CO2 
 
William C. Chueh, Sossina M. Haile 
 
Supporting Information 
 
                 
2 
0 1 2 3 4 5
0
1
2
3
4
5
6
600
800
1000
1200
1400
1600
 
T
em
p
er
a
tu
re
 (
° 
C
)
O
2 
R
at
e 
(s
cc
m
 g
-1
   
  )
t (min)
C
eO
2
 
 
Fig. S1. Oxygen release rate from fully oxidized CeO2 upon rapid heating from 700 to 1500 °C 
in an infrared furnace under flowing 11 ppm O2 in N2 supplied at a flow rate of  
1470 sccm g-1CeO2. Oxygen evolution was rapid and limited by the ramp rate of the furnace. 
Integrating the rate curve gives an oxygen nonstoichiometry of 0.06.  
The sample was fabricated in the same way as indicated in the Experimental section. An alumina 
tube (9.5 mm inner diameter) served as the reactor with the exhaust gas connected to a Pfeiffer 
Thermostar quadrupole mass spectrometer.  
3 
Ni-SDC 
Temperature 
(ºC) 
VH2 (mL g
-1) VCH4 (mL g
-1) VCO (mL g
-1) SCH4 (%) X 
400 1.0 ± 0.1 1.1 ± 0.1 0.05 ± 0.01 80 0.8 ± 0.1 
500 3.2 ± 0.3 0.7 ± 0.1 0.28 ± 0.02 46 1.0 ± 0.1 
600 4.3 ± 0.3 0.30 ± 0.02 1.3 ± 0.1 18 1.1 ± 0.1 
700 4.1 ± 0.3 0 1.9 ± 0.2 0.2 0.9 ± 0.1 
Table S1(a). Fuel productivity and extent of reaction data corresponding to Fig. 2(top). 
SDC 
Temperature 
(ºC) 
VH2 (mL g
-1) VCH4 (mL g
-1) VCO (mL g
-1) SCH4 (%) X 
400 4.7 ± 0.4 0 0.36 ± 0.08 0 0.8 ± 0.1 
500 4.5 ± 0.4 0 1.8 ± 0.1 0 1.0 ± 0.1 
600 3.9 ± 0.3 0 1.8 ± 0.1 0 0.9 ± 0.1 
700 4.1 ± 0.3 0 2.0 ± 0.2 0 0.9 ± 0.1 
Table S1(b). Fuel productivity and extent of reaction data corresponding to Fig. 2(bottom) 
V is the total volume of gas produced, SCH4 is the methane selectivity, defined as SCH4 = 
4VCH4/(4VCH4+VH2+VCO) and X is the extent of reaction, defined as the ratio of fuel produced to 
the theoretical fuel productivity, as set by the initial oxygen nonstoichiometry.  
4 
0 2 4 6 8 10
0
1
2
3
4
5
SDC
S
D
C
700 ºC, pH
2
O = 0.064 atm, FR
tot 
= 380 sccm g-1
R
at
e 
(s
cc
m
 g
-1
  
 )
 
 
 
t (min)
 Cycle 1
 Cycle 31
 Cycle 53
 
Cycle No. VH2 (mL g
-1) X 
1 7.6 ± 0.6 1.2 ± 0.1 
31 7.6 ± 0.6 1.2 ± 0.1 
53 7.7 ± 0.6 1.2 ± 0.1 
 
Fig. S2 / Table S2. H2 production as a function of time, as measured by gas chromatography 
upon exposure of reduced SDC to mildly humidified N2/Ar at the conditions indicated (FRtot is 
the total flow rate). Efficacy of H2O splitting is largely unchanged after 53 redox cycles (other 
cycles at various conditions). V is the total volume of gas produced, SCH4 is the methane 
selectivity, defined as SCH4 = 4VCH4/(4VCH4+VH2+VCO) and X is the extent of reaction, defined as 
the ratio of fuel produced to the theoretical fuel productivity, as set by the initial oxygen 
nonstoichiometry.  
 
5 
0 5 10 15 20
0.0
0.1
0.2
0.3
0.4
0.5
SDC
S
D
C
R
at
e 
(s
cc
m
 g
-1
  
 )
t (min)
500 ºC, pH
2
O = 0.064 atm
pCO
2
 = 0.032 atm, FR
tot 
= 10 sccm g-1
 
CO
CH
4
Cycle 1
Cycle 6
Cycle 11
H
2
 
Cycle No. VH2 (mL g
-1) VCH4 (mL g
-1) VCO (mL g
-1) SCH4 (%) X 
1 3.5 ± 0.3 0.74 ± 0.06 0.31 ± 0.02 44 1.0 ± 0.1 
6 3.2 ± 0.3 0.74 ± 0.06 0.28 ± 0.02 46 1.0 ± 0.1 
11 3.4 ± 0.3 0.81 ± 0.07 0.23 ± 0.02 47 1.0 ± 0.1 
 
Fig. S3 / Table S3. Fuel production as a function of time, as measured by gas chromatography, 
upon simultaneous exposure of reduced Ni-SDC to H2O and CO2 (balance Ar/N2) at the 
conditions indicated (FRtot is the total flow rate). Fuel production curves as well as CH4 
selectivity are stable after 11 redox cycles (other cycles at various conditions). V is the total 
volume of gas produced, S is the selectivity, defined as…. and X is the extent of reaction, 
defined as… 
6 
                       
1.0 1.1 1.2 1.3
-0.8
-0.4
0.0
0.4
700 600 500
S
D
C
 H
2
O Splitting, P
H2O 
= 0.064 atm
 CO
2
 Splitting, P
CO2
 = 0.032 atm
0.80 ± 0.02 eV
T (ºC)
 
Lo
g 
(r
in
it /
 s
cc
m
 g
-1
  
 )
1000 T-1 (K-1)
0.52 ± 0.02 eV
 
                         
-2.0 -1.8 -1.6 -1.4 -1.2 -1.0
-0.6
-0.4
-0.2
0.0
0.2
S
D
C
 H
2
O Splitting
 CO
2
 Splitting
T = 600 ºC
 
0.77 ± 0.02  
Lo
g 
(r
in
it /
 s
cc
m
 g
-1
  
 )
Log (P
i
 / atm)
0.54 ± 0.01
 
Fig. S4. Initial production rates of H2 and CO as functions of (a) temperature and (b) reactant 
partial pressures when H2O and CO2 are individually reacted with reduced SDC, respectively. 
The rates shown here correspond to that at t = 0. We take the initial state in all cases to 
correspond to the same value of oxygen nonstoichiometry. 
(a) 
(b) 
7 
The instantaneous reactant conversion rate was kept below 20 % to satisfy the gradient-less 
reactor and isothermal approximations (ΔT < 3 °C) (Fig. S2). To avoid equilibrium limitations in 
the fuel production reactions, reactant flow rates were kept sufficiently high such that the 
2 2
:H O Hp p  and 2 :CO COp p  ratios at the exhaust were always above 9 (for determining reaction 
orders) and above 5 (for determining activation energies).   
8 
                             
0 2 4 6
0
2
4
6
8
SDC
SDC
S
D
C
800 ºC, pH
2
O = 0.064 atm, FR
tot 
= 380 sccm g-1
t (min)
H
2 
R
at
e 
(s
cc
m
 g
-1
  
 )
 
 
7.5 ± 0.6 mL g-1
 
 
                             
0 2 4 6 8 10
0
1
2
3
4
5
6
SDC
S
D
C
  
t (min)
H
2 
R
at
e 
(s
cc
m
 g
-1
  
 )
T = 750 ºC, P
H2O
 = 0.023 atm, FR
tot
 = 200 sccm g-1
 
 SDC
 2 wt% Rh-SDC
 
Fig. S5. (a) H2 production rate as a function of time, as measured by gas chromatography, upon 
exposure of reduced SDC to mildly humidified N2/Ar at the conditions indicated (FRtot is the 
total flow rate). The total quantitiy of hydrogen produced (value indicated) implies an extent of 
reaction X  = 1.2 ± 0.1. (b) Comparison of H2 fuel production curves for SDC with and without 2 
wt% Rh..  
 
 
(a) 
(b) 
9 
0 2 4 6 8 10
0
2
4
SDC
SDC
S
D
C
800 ºC, pCO
2
 = 0.032 atm, FR
tot 
= 300 sccm g-1
C
O
 R
at
e 
(s
cc
m
 g
-1
  
 )
t (min)
 
 
7.0 ± 0.6 mL g-1
 
Fig. S6 CO production rate as a function of time, as measured by gas chromatography, upon 
reaction of CO2 with reduced SDC at the conditions indicated (FRtot is the total flow rate). No C 
was detected as verified by post situ TPO. Total quantity of CO produced (value indicated) 
implies an extent of reaction of X  = 1.1 ± 0.1. 
10 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                   
 
Fig. S7. Equilibrium compositions calculated at 1 atm for the starting materials indicated 
with
2H O
p = 0.064 atm and 
2CO
p = 0.032 atm.
200 400 600 800
0.00
0.10
0.20
0.30
0.40
0.50
 
M
ol
e
H
2
T(ºC)
Starting Materials: 
0.5 mole H
2
O
10 mole SDC (= 0.05) (a)
200 400 600 800
 
 
 
 
H
2
0.5 moles H
2
O
10,000 moles SDC (= 0.05) (b)
0.00
0.05
0.10
0.15
0.20
0.25
M
ol
e
C(gr)
CO
0.25 mole CO
2
,
10 mole SDC ( = 0.05)
(c)
 
 
C(gr) CO
0.25 moles CO
2
,
10,000 mole SDC (= 0.05)
(d)
200 400 600 800
0.00
0.05
0.10
0.15
0.20
0.25
M
ol
e
T (ºC)
H
2
CH
4
C(gr) CO
0.25 mole H
2
O
0.125 mole CO
2
10 mole 
SDC (= 0.05)
(e)
200 400 600 800
 
H
2
CH
4 C(gr) CO
0.25 mole H
2
O
0.125 mole CO
2
10,000 mole 
SDC (= 0.05)
(f)
11 
                   
0 5 10 15
0.0
0.2
0.4
SDC
S
D
C
R
at
e 
(s
cc
m
 g
-1
  
 )
t (min)
 
 
 H
2
 CH
4
 CO
900 ºC, pH
2
O = 0.132 atm, pCO
2
 = 0.066 atm
FR
tot 
= 40 sccm g-1
S
D
C
Im
pl
ie
d 
R
at
e 
of
 C
(s
) 
D
ep
os
iti
on
 (

m
in
-1
 g
-1
  
 )
-4
0
4
 
 
 
Fig. S8. (Top) Implied rate of C(s) deposition that occurs upon reaction of H2O and CO2 with 
reduced 10 wt% Ni-SDC at the conditions indicated; and (bottom) fuel production rates. Solid 
carbon formation rate is calculated by taking the difference between the carbon in the the product 
gases and that in the reactants. Integration of the carbon formation rate curve with time indicates 
zero carbon accumulation (within error).  
 
12 
 
Process Temperatures 
(° C) 
Energy 
 (kJ mol-1 Syngas**) 
Heating oxidized SDC  800 → 1500 1431.7 
Reduction of SDC (oxygen release)  1500 412.2 
Cooling reduced SDC  1500 → 800 -1425.1 
Cooling O2(g) 1500 → 25 -25.3 
Heating H2O(l) & CO2(g) 25 → 800 122.3 
Oxidation of SDC (fuel production) 800 -140.2 
Cooling Excess H2O(g) & CO2(g) 800 → 25 -61.2 
Cooling H2(g) & CO(g) 800 → 25 -23.3 
Total energy input  1966.2 
Net energy output  291.2 
Efficiency  14.8% 
** 1 mole of syngas = 2/3 mole of H2 and 1/3 mole of CO. 
Table S4. Following a methodology reported in the literature (1-2), the cycle efficiency for 
syngas production from H2O and CO2 using thermal energy was calculated as the ratio of the 
energy content of the output fuel to the various energy inputs. The oxygen release and H2O/CO2 
splitting half-cycle temperatures were taken to be 1500 °C and 800 °C, respectively. Ceria was 
assumed to attain a nonstoichiometry, , of 0.05 after the reduction step, and chemical reaction 
was assumed to reach equilibrium.  
13 
Solar absorption efficiency (88.8 %) was determined by assuming a blackbody receiver with a 
solar radiation intensity of 1 kW m-2 and a concentration ratio of 5,000 suns in the solar 
concentrator. Assuming no heat recovery, a total cycle efficiency of 13.2 % is obtained. A 
similar result is obtained if one considers the energy content of the synthesized fuel as the net 
energy output. With 50 % heat recovery, the efficiency increases to 22.9 %. 
Some amount of N2 with low oxygen content will be required to prevent oxidation of ceria and 
the product. The energy cost for N2 separation from air is typically ~ 20 kJ/mol (3).  
 
Supplementary References 
S1. A. Steinfeld, , S. Sanders, R. Palumbo, Energy 1999, 65, 43.  
S2.  C. Perkins, A.W. Weimer, Int. J. Hydrogen Energy 2004, 29, 1587. 
S3.  H-W. Haring in Industrial Gases Processing, 2008.  
 
 


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Ceria as a Thermochemical Reaction Medium for Selectively Generating Syngas or Methane from H_2O and CO_2

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