Tuning CO2 methanation selectivity via MgO/Ni interfacial sites

Abstract

CO2 methanation is a promising carbon–neutral process to produce synthetic natural gas. Ni is a cost-effective catalyst, but needs improved selectivity to compete with noble metal catalysts. Herein, MgO-promoted Ni/SiO2 is investigated as model system and compared to unpromoted Ni/SiO2. The catalysts are characterized with chemisorption, transmission electron microscopy and in situ quick X-ray absorption spectroscopy. After reduction, MgO partly covers metallic Ni forming an MgO/Ni interface, which proves to be critical to the reaction through metal oxide-metal interaction. Combining kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy, formyl group hydrogenation was found to be the rate determining step for both catalysts. The enhanced CH4 selectivity after MgO addition is attributed to facilitated conversion of the key intermediates - formyl groups - due to a lower energy barrier. This work provides unambiguous experimental proof for the role of the MgO/Ni interface in the reactivity for CO2 methanation.