Effect of water density on heterogeneous catalytic water gas shift reaction in the presence of Ru/C, Pd/LaCoO3 and Fe3O4 in supercritical water

• Heterocatalytic water gas shift reaction was examined in supercritical water.
• The catalysts used were Ru/C, Pd/LaCoO3 and Fe3O4.
• Water gas shift reaction was suppressed in high water density region.
• The reaction model considering fugacity and water density effect was proposed.
• The coverage of water on active sites of catalyst would suppress the reaction.

Water gas shift reaction in the presence of heterogeneous catalysts such as Ru/C, Pd/LaCoO3 and Fe3O4 was examined in supercritical water at 673 K from 0.1 to 0.5 g/cm3 of water densities. These catalysts catalyzed water gas shift reaction and the main products were CO2 and H2. CH4 was formed from CO and H2 produced by water gas shift reaction in the presence of Ru/C. CO conversion tended to decrease with increasing water density for all catalysts, which means that water essentially suppressed heterogeneous catalytic water gas shift reaction in supercritical water. The kinetics of water gas shift reaction was analyzed with an elementary-like reaction model using fugacity. The model calculation represented the trend of experimental results and revealed that the suppression of water gas shift reaction in high water density region was probably because water would cover on active sites and stabilize the adsorbed species on catalyst to decrease the ratio of vacancy of active sites on catalyst.

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