CO2 hydrogenation selectivity shift over In-Co binary oxides catalysts: Catalytic mechanism and structure-property relationship

Abstract

The hydrogenation of CO2 into methanol has attracted much attention and In2O3 is a promising catalyst. Introducing metal elements into In2O3 (M/In2O3) is one of the main strategies to improve its performance. However, its mechanism and active sites remain unclear and need to be further elucidated. Here, the noble-metal-free Inx-Coy oxides catalysts were prepared. Much-improved performance and obvious product selectivity shift were observed. The optimized catalyst (In1-Co4) (9.7 mmol gcat−1 h−1) showed five times methanol yields than pure In2O3 (2.2 mmol gcat−1 h−1) (P = 4.0 MPa, T = 300 °C, GHSV = 24000 cm3STP gcat−1 h−1, H2:CO2 = 3). And the cobalt-catalyzed CO2 methanation activity was suppressed, although cobalt was most of the metal element. To unravel this selectivity shift, detailed catalysts performance evaluation, together with several in-situ and ex-situ characterizations, were employed on cobalt and In-Co for comparative study. The results indicated CO2 hydrogenation on cobalt and In-Co catalyst both followed the formate pathway, and In-Co reconstructed and generated a surface In2O3-enriched core-shell-like structure under a reductive atmosphere. The enriched In2O3 at the surface significantly enhanced CO2 adsorption capacity and well stabilized the intermediates of CO2 hydrogenation. CO2 and carbon-containing intermediates adsorbed much stronger on In-Co than cobalt led to a feasible surface C/H ratio, thus allowing the *CH3O to desorb to produce CH3OH instead of being over-hydrogenated to CH4.