Effect of ceria and strontia over Ru/Mn/Al2O3 catalyst: Catalytic methanation, physicochemical and mechanistic studies

• The addition of Ce to RuMn/Al2O3 has a positive effect on the activity and stability.
• The CeO2, SrO2, RuO2, Mn2O3 and orthorhombic Al2O3 were the active species.
• The Sr4(Ru2O9) compound had decreased the reducibility and basicity of catalyst.
• The mechanistic study in this research depends on the type of based catalysts.
• The Sr4(Ru2O9) compound responsible for the formation of carbonate and formate species.

The 65 wt% of ceria and strontia based catalysts prepared by impregnation with RuMn/Al2O3 were tested on its CO2 methanation reaction under reducing pretreatment at 300 °C. The result obtained revealed that the addition of Ce to RuMn/Al2O3 has a positive effect on the activity and catalyst stability compared to the Sr containing catalyst. The CO2 conversion over Ru/Mn/Ce-65/Al2O3 achieved 97.73% with 91.31% of methane formation at a reaction temperature of 200 °C while, 73.10% conversion over Ru/Mn/Sr-65/Al2O3 catalyst with 44.58% of methane yielded at reaction temperature of 210 °C. The characterization results obtained suggest that the CeO2, SrO2, RuO2, Mn2O3 and orthorhombic Al2O3 were the active species for both catalysts while, the presence of spinel compound, Sr4(Ru2O9) caused the reducibility and basicity of Ru/Mn/Sr-65/Al2O3 catalyst decreased hence reduced the catalytic activity eventually. The mechanistic study showed it was depended on the type of catalysts as the CO2 adsorbed on the Sr based catalyst tended to form monodentate carbonate at the initial state before forming the formate species when it was hydrogenated and finally releasing the methane. Meanwhile, the methane formation on Ce based catalyst involved the initially adsorption and dissociation of CO2 into C and O adsorbed species before reacting with the adsorbed H2 to form methane gas.

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