Syngas production by methane tri-reforming: Effect of Ni/CeO2 synthesis method on oxygen vacancies and coke formation

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The CH4 tri-reforming process can contribute to mitigating CO2 emissions and enables the formation of syngas with different H2/CO ratios. Ni catalysts supported on CeO2 were synthesized by hydrothermal and ionothermal methods and were applied in methane tri-reforming reactions with GHSV of 48,000 mL/g.h, at atmospheric pressure and temperature of 800 °C. The catalytic activity in the tri-reforming reaction was enhanced by changing the morphological properties of the catalyst by appropriate selection of the amount of ionic liquid used in the synthesis procedure. Changing the composition resulted in methane conversion increasing from 60 % to 95 % and carbon dioxide conversion increasing from 40 % to 55 %. Increased Ni dispersion was related to the oxygen vacancies on the Ni-Ce surface, which created interfacial active sites. The results of XANES combined with XPS revealed that a partial reduction of Ni species contributed to high hydrogen yields, due to the distribution of active sites over the catalyst surface. These sites remained active during 5 h, demonstrating the positive effect of the ionic liquid used in the CeO2 synthesis. In addition, post-reaction characterization results showed Ni re-oxidation on the ceria support produced without ionic liquid.