Promoting effect of Fe on supported Ni catalysts in CO2 methanation by in situ DRIFTS and DFT study

Bimetallic NiFe catalysts have emerged as a promising alternative to the traditional Ni catalysts for CO2 methanation. However, the promoting effect of Fe on the bimetallic catalysts remains ambiguous. In this study, a series of NiFe catalysts derived from hydrotalcite precursors were investigated. In situ x-ray diffraction (XRD) analysis revealed that small NiFe alloy particles were formed and remained stable during reaction. When Fe/Ni = 0.25, the alloy catalysts exhibited the highest CO2 conversion, CH4 selectivity and stability in CO2 methanation at low temperature of 250-350 degrees C. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study indicated that the formate pathway was the most plausible reaction scheme on both Ni and NiFe alloy catalysts, while a moderate addition of Fe facilitated the activation of CO2 via hydrogenation to *HCOO. Density functional theory (DFT) calculations further demonstrated that the overall energy barrier for CH4 formation was lower on the alloy surface. (C) 2020 The Author(s). Published by Elsevier Inc.