Promotional effects of Ru and Fe on Ni/ZrO2 catalyst during CO2 methanation: A comparative evaluation of the mechanism

Ni-based catalysts are widely investigated non-noble metal-based systems for CO2 methanation. However, their industrial application is still limited due to lower activity at low-temperature and catalyst deactivation. Incorporating a second metal such as Ru and Fe is considered as a successful strategy to overcome these challenges through alloy formation or the synergies provided by the interplay of two adjacent metallic sites. Nonetheless, their promotional effect on the CO2 methanation mechanism under similar conditions has not been reported yet. In this work, Fe and Ru-promoted Ni/ZrO2 catalysts were investigated to evaluate their promotional effect on the mechanism. The Ni/Fe ratio was first optimized and a CO2 conversion rate of 37.7 mmolCO2/(molNi+Fe s) and 96.3% CH4 selectivity was obtained over the Ni0.8Fe0.2/ZrO2 catalyst. In comparison with Ni0.8Fe0.2/ZrO2, Ni0.8Ru0.2/ZrO2 prepared with the same composition showed higher activity and stability in CO2 methanation. Characterization results indicate alloys formation and H spillover for Ni0.8Ru0.2/ZrO2 to be responsible for promotion. Besides, in situ DRIFTS studies evidenced the occurrence of both CO2 dissociative and associative pathways over Ni0.8Ru0.2/ZrO2 catalyst, while solely the CO2 associative pathway occurred for Ni0.8Fe0.2/ZrO2.