The formate and redox mechanisms of water-gas shift reaction on the surface of Ag: A nanocluster model based on DFT study

Abstract

Two different possible mechanisms of water gas shift reaction including formate and redox mechanisms on the Ag₅ cluster were investigated using DFT computations. All the elementary steps involved in both mechanisms were considered. It was observed that dissociation of H₂O_ads and OH_ads, as well as formation of CO_2(ads), required activation energy. For these steps, transition state structures were determined and their corresponding activation energies were calculated. For both mechanisms, the highest activation energy (402.34 kJ mol^-1) was related to the dissociation of OH_ads as the rate limiting step. The calculated activation energy of CO_2(ads) formation according to the redox mechanism (COads + O ads → CO2(ads)) was 9.32 kJ mol^-1 indicating that this step was relatively fast on the surface of Ag₅ cluster. It was observed that, CO_2(ads) formation according to the formate mechanism occurred through three consecutive steps where the dissociation of formate (HCOO(ads) → CO2(ads) + Hads) had the highest activation energy, 171.53 kJ mol^-1.