Abstract
AbstractA multiscale analysis combining density functional theory (DFT) and microkinetic modeling is performed to resolve the uncertainties in CO2 methanation reaction mechanism and kinetics on popular Ni and Ru catalysts. The most debated issues are the activation routes of CO2 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 CO2, 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 CO2* 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 CH3* hydrogenation to CH4, respectively. We further find that selectivity of the reaction on Ni is higher than that on Ru, whereas activity of Ru is higher.
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