Doping Ni/USY zeolite catalysts with transition metals for CO2 methanation

The introduction of rare-earth metal oxides into nickel-based catalysts to increase their activity, selectivity and stability in carbon dioxide methanation is critical for their potential industrial application. Alternatively, cheaper and more abundant transition metals, such as Fe and Cu, could enhance Ni catalysts performance. In this work, Ni-based catalysts (15 wt%) doped with Cu (1 wt%) and Fe (1, 2 and 3 wt%) supported on an optimized USY zeolite were prepared by incipient wetness co-impregnation, characterized by XRD, TGA, N2 adsorption, H2-TPR, and TEM, and finally tested towards CO2 methanation (total flow of 274 mL/min, P = 5 bar and 0.2 g of catalyst). In addition, reference catalysts containing 15 wt% Ni, Cu or Fe were prepared and analysed using the same previously described techniques. Copper, which exhibited lower activity than Ni in the studied reaction (31 vs 83 % CH4 yield at 375 °C), did not lead to an enhancement of Ni/Zeolite activity, which was due to a lack of improvements on the catalysts' physicochemical properties. On the contrary, despite the lack of activity of Fe towards towards CO2 methanation, its addition to Ni/Zeolite catalysts led to a significant improvement in catalytic activity (60 vs 91% CH4 yield at 350 °C). This effect was ascribed to the formation of smaller (8.1 nm) and better dispersed (5.9 %) Ni0 particles and the establishment of stronger Ni-support interactions.