CO2 methanation combined with NH3 decomposition by in situ H2 separation using a Pd membrane reactor

•One pot synthesis of CH4 from NH3 and CO2 was performed by a Pd membrane reactor.•CO2 methanation significantly enhanced H2 removal rate.•High CH4 selectivity in CO2 methanation could be achieved by in situ H2 separation.

Combination of the reactions by means of membrane separation techniques are of interest. The CO2 methanation was combined with NH3 decomposition by in situ H2 separation through a Pd membrane. The CO2 methanation reaction in the permeate side was found to significantly enhance the H2 removal rate of Pd membrane compared to the use of sweep gas. The reaction rate of CO2 methanation was not influenced by H2 supply through the Pd membrane in contrast to NH3 decomposition in the retentate side. However, the CH4 selectivity could be improved by using a membrane separation technique. This would be caused by the active dissociated H species which might immediately react with adsorbed CO species on the catalysts to CH4 before those CO species desorbed. From the reactor configuration tests, the countercurrent mode showed higher H2 removal rate in the combined reaction at 673 K compared to the cocurrent mode but the reaction rate in CO2 methanation should be improved to maximize the perfomance of membrane reactor.