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

Abstract

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.