Mechanism of Methanol Synthesis from CO<sub>2</sub> Hydrogenation over Pt<sub>8</sub>/In<sub>2</sub>O<sub>3</sub> Catalysts: A Combined Study on Density Functional Theory and Microkinetic Modeling
Xiaowen Wang, Jiaying Pan, Haiqiao Wei, Wenjia Li, Jun Zhao, Zhen Hu
Abstract
In2O3-based catalysts have attracted considerable attention in CO2 hydrogenation to methanol reactions, thanks to their excellent CO2 conversion rate and methanol selectivity. In this work, density functional theory combined with microkinetic modeling is employed to investigate the methanol synthesis mechanism over a Pt8/In2O3 catalyst. First, a stable Pt8/In2O3 (110) catalyst is modeled, where the Pt8 cluster is positively charged. Second, the adsorption properties of the reaction species are optimized. It shows that H2 is dissociated spontaneously to two H* adatoms on the Pt8 cluster and the CO2* is adsorbed at the interface of Pt8/In2O3. Then three methanol synthesis channels are tested, that is, formate (HCOO), carboxyl (COOH), and RWGS + CO-Hydro routes. The calculations indicate that methanol is produced along with the order of CO2* → COOH* → CO* + OH* → HCO* → H2CO* → H2COH* → H3COH*. Finally, the channel is subjected to the microkinetic calculation at a pressure of 5 MPa and in a temperature range of 423 to 873 K. The degree of rate control analysis shows that H* adatom and COOH* dissociation TS7 are the rate-controlling adsorption and transition states, respectively. With the elevation of temperature, the turnover frequencies of CO and CH3OH increase, and the CH3OH selectivity decreases. They are related to the coverage of H* and COOH*.