Investigating CO<sub>2</sub> Methanation on Ni and Ru: DFT Assisted Microkinetic Analysis
Ojus Mohan, Shambhawi Shambhawi, Rong Xu, Alexei A. Lapkin, Samir H. Mushrif
Abstract
Abstract A multiscale analysis combining density functional theory (DFT) and microkinetic modeling is performed to resolve the uncertainties in CO 2 methanation reaction mechanism and kinetics on popular Ni and Ru catalysts. The most debated issues are the activation routes of CO 2 and CO (hydrogenation or direct dissociation) and whether the reaction proceeds with or without forming a CO* intermediate. We investigated a comprehensive reaction network of 46 elementary reactions, involving multiple CO 2 , CO activation routes and side reactions using a benchmarked DFT functional. Our study shows that the dominant pathway at 550 K and 10 atm includes direct dissociation of CO 2 * to CO* on both Ni and Ru surfaces. On Ru, CO* undergoes hydrogenation to form COH* that further dissociates to C*, whereas on Ni, HCO* is formed that gives CH* upon dissociation. The rate determining steps on Ni and Ru are HCO* dissociation to CH* and O* and CH 3 * hydrogenation to CH 4 , respectively. We further find that selectivity of the reaction on Ni is higher than that on Ru, whereas activity of Ru is higher.