Multiscale Investigation of the Mechanism and Selectivity of CO2 Hydrogenation over Rh(111)

Shijia Sun; Michael D Higham; Xingfan Zhang; C Richard A Catlow

doi:10.1021/acscatal.3c05939

Multiscale Investigation of the Mechanism and Selectivity of CO₂ Hydrogenation over Rh(111)

ACS Catal. 2024 Mar 28;14(8):5503-5519. doi: 10.1021/acscatal.3c05939. eCollection 2024 Apr 19.

Authors

Shijia Sun¹, Michael D Higham^{1

2}, Xingfan Zhang¹, C Richard A Catlow^{1

2

3}

Affiliations

¹ Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, London WC1H 0AJ, United Kingdom.
² Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell, Oxon OX11 0FA, United Kingdom.
³ School of Chemistry, Cardiff University, Park Place, Cardiff CF10 1AT, United Kingdom.

Abstract

CO₂ hydrogenation over Rh catalysts comprises multiple reaction pathways, presenting a wide range of possible intermediates and end products, with selectivity toward either CO or methane being of particular interest. We investigate in detail the reaction mechanism of CO₂ hydrogenation to the single-carbon (C1) products on the Rh(111) facet by performing periodic density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations, which account for the adsorbate interactions through a cluster expansion approach. We observe that Rh readily facilitates the dissociation of hydrogen, thus contributing to the subsequent hydrogenation processes. The reverse water-gas shift (RWGS) reaction occurs via three different reaction pathways, with CO hydrogenation to the COH intermediate being a key step for CO₂ methanation. The effects of temperature, pressure, and the composition ratio of the gas reactant feed are considered. Temperature plays a pivotal role in determining the surface coverage and adsorbate composition, with competitive adsorption between CO and H species influencing the product distribution. The observed adlayer configurations indicate that the adsorbed CO species are separated by adsorbed H atoms, with a high ratio of H to CO coverage on the Rh(111) surface being essential to promote CO₂ methanation.