Notably, DRM converts two major greenhouse gases, CO 2 and CH 4 , into useful
syngas. The H 2 /CO ratio is 1, which is lower than that achieved by steam
reforming, and even lower than the ideal ratio for FT (2.05–2.15). By combining
reactions 2.5 and 2.8 with reaction 2.9, it is possible to adjust the H 2 /CO ratio to the
most suited value. The major technological challenges for the industrial application
of DRM are its high endothermicity, requiring high temperatures for appreciable
conversion, and the deactivation of catalysts under reaction conditions, caused by
coking or sintering. The high-energy input required by the process causes a serious
penalty if fossil-C has to be used as source of energy and calls for using solar
heating to supplement the required energy. For industrial application of DRM,
cost-effective catalysts must be developed that can maintain a stable performance
for long time. In the past decade, there has been a substantial increase in research
focus on catalyst development for DRM and tremendous progress has been made in
increasing the activity and stability of catalysts even in a plasma environment [8].
The high endothermicity of the reaction is due to the fact that both CH 4 and CO 2
are very stable molecules with high bond dissociation energy (435 kJ/mol for CH 3 –
H and 526 kJ mol
−1 for CO–O), so that high temperatures (>800 °C) are required.
Moreover, the H 2 /CO ratio is influenced by the simultaneous occurrence of “Reverse Water Gas Shift-RWGS” reaction (Eq. 2.10) which further lowers the H 2 /CO
ratio to <1 by producing water.
H 2 þ CO 2 ! H 2 O þ CO
ð2:10Þ
Based on the relative endothermicity of the DRM and RWGS reactions, the effect
of RWGS on product selectivity is more significant in the temperature range
400–800 °C [9]. Other significant side reactions in DRM are methane decomposition
(Eq. 2.11) and the CO disproportionation (Boudouard equilibrium) (Eq. 2.12).
CH 4 ! C þ 2H 2 DH 298 ¼ 75 kJ mol
À1
ð2:11Þ
2CO C þ CO 2
ð2:12Þ
Both reactions 2.11 and 2.12 produce solid carbon (or coke) that can cover the
catalyst (coking) and cause rapid deactivation in the temperature range of 557–700
°C (methane decomposition) (Boudouard reaction) [10]. It looks like the optimum
temperature at the feed ratio of CO 2 /CH 4 = 1:1 is between 870 and 1040 °C,
considering the formation and conversion of carbon. Modeling the reaction has
confirmed that the optimum working temperature is 850 °C at low pressures for a
high conversion [9]. Syngas is largely used in catalytic FT processes for Cn
hydrocarbon (Eq. 2.13), olefin (Eq. 2.14), and alcohol (Eq. 2.15) production.
nCO þ 2n þ 1
ð
ÞH 2 ¼ C n H 2n þ 2 þ nH 2 O
ð2:13Þ
nCO þ 2nH 2 ¼ C n H 2n þ nH 2 O
ð2:14Þ
2.3 Carbon Dioxide Emissions
23
syngas. The H 2 /CO ratio is 1, which is lower than that achieved by steam
reforming, and even lower than the ideal ratio for FT (2.05–2.15). By combining
reactions 2.5 and 2.8 with reaction 2.9, it is possible to adjust the H 2 /CO ratio to the
most suited value. The major technological challenges for the industrial application
of DRM are its high endothermicity, requiring high temperatures for appreciable
conversion, and the deactivation of catalysts under reaction conditions, caused by
coking or sintering. The high-energy input required by the process causes a serious
penalty if fossil-C has to be used as source of energy and calls for using solar
heating to supplement the required energy. For industrial application of DRM,
cost-effective catalysts must be developed that can maintain a stable performance
for long time. In the past decade, there has been a substantial increase in research
focus on catalyst development for DRM and tremendous progress has been made in
increasing the activity and stability of catalysts even in a plasma environment [8].
The high endothermicity of the reaction is due to the fact that both CH 4 and CO 2
are very stable molecules with high bond dissociation energy (435 kJ/mol for CH 3 –
H and 526 kJ mol
−1 for CO–O), so that high temperatures (>800 °C) are required.
Moreover, the H 2 /CO ratio is influenced by the simultaneous occurrence of “Reverse Water Gas Shift-RWGS” reaction (Eq. 2.10) which further lowers the H 2 /CO
ratio to <1 by producing water.
H 2 þ CO 2 ! H 2 O þ CO
ð2:10Þ
Based on the relative endothermicity of the DRM and RWGS reactions, the effect
of RWGS on product selectivity is more significant in the temperature range
400–800 °C [9]. Other significant side reactions in DRM are methane decomposition
(Eq. 2.11) and the CO disproportionation (Boudouard equilibrium) (Eq. 2.12).
CH 4 ! C þ 2H 2 DH 298 ¼ 75 kJ mol
À1
ð2:11Þ
2CO C þ CO 2
ð2:12Þ
Both reactions 2.11 and 2.12 produce solid carbon (or coke) that can cover the
catalyst (coking) and cause rapid deactivation in the temperature range of 557–700
°C (methane decomposition) (Boudouard reaction) [10]. It looks like the optimum
temperature at the feed ratio of CO 2 /CH 4 = 1:1 is between 870 and 1040 °C,
considering the formation and conversion of carbon. Modeling the reaction has
confirmed that the optimum working temperature is 850 °C at low pressures for a
high conversion [9]. Syngas is largely used in catalytic FT processes for Cn
hydrocarbon (Eq. 2.13), olefin (Eq. 2.14), and alcohol (Eq. 2.15) production.
nCO þ 2n þ 1
ð
ÞH 2 ¼ C n H 2n þ 2 þ nH 2 O
ð2:13Þ
nCO þ 2nH 2 ¼ C n H 2n þ nH 2 O
ð2:14Þ
2.3 Carbon Dioxide Emissions
23