Exploration of the active sites on a Rh-In2O3 catalyst for the semi-hydrogenation of acetylene: a theoretical study

Indium oxide with oxygen vacancies and the platinum-promoted In2O3 catalyst have been reported in the literature to be active for the semi-hydrogenation of acetylene to ethylene. In this work, a rhodium (Rh)-promoted catalyst was investigated for the semi-hydrogenation of acetylene to ethylene using density functional theory calculations. In2O3-supported Rh4 and the Rh single atom-promoted In2O3 catalysts were constructed. The presence of the Rh single atom alters the structure of the pristine oxygen vacancy of In2O3 and provides active 4d orbitals. The oxygen vacancy with the electronic modification by the Rh single atom enhanced H2 activation and C2H2 adsorption. The produced C2H4 over the oxygen vacancy with the Rh single atom prefers to be desorbed from the active site to gas phase rather than be over-hydrogenated to C2H6. However, the Rh4 site over the defective Rh4/In2O3 catalyst facilitates the formation of C2H6 due to the strong C2H4 adsorption and low activation barrier of over-hydrogenation. Moreover, the oxygen vacancy over the defective Rh4/In2O3 catalyst cannot be active for acetylene hydrogenation solely due to the poor adsorption for H2 and C2H2 with the huge activation barrier of C2H2 hydrogenation. This work will inspire the rational design of Rh-promoted In2O3 catalysts for the semi-hydrogenation of acetylene to ethylene.