CO2 methanation mechanism over Ni/Y2O3: an in situ diffuse reflectance infrared Fourier transform spectroscopic study

Abstract

Supported Ni catalysts are active in CO₂ methanation. It is important to understand the reaction mechanism for the development of highly-active catalysts. In this study, we investigated the reaction pathways of CO₂ methanation over Ni/Y₂O₃ and Ni/Al₂O₃ based on the adsorbates observed by diffuse reflectance infrared Fourier transform spectroscopy. For Ni/Al₂O₃, linear and bridged CO adsorbates were converted to nickel carbonyl hydride and/or formyl species, which would be further hydrogenated to methane. In contrast, the formation of formate adsorbates was specifically confirmed over Ni/Y₂O₃ under the CO₂ methanation condition. The hydrogen molecule was activated by dissociatively-adsorbing on Ni particles. Then, the hydrogenation of formate adsorbates by the activated hydrogen species proceeded sequentially to form methane. The observed bridged CO species would not be a major intermediate for Ni/Y₂O₃.