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

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 In_x-Co_y oxides catalysts were prepared. Much-improved performance and obvious product selectivity shift were observed. The optimized catalyst (In₁-Co₄) (9.7 mmol g_cat⁻¹ h⁻¹) showed five times methanol yields than pure In₂O₃ (2.2 mmol g_cat⁻¹ h⁻¹) (P = 4.0 MPa, T = 300 °C, GHSV = 24000 cm³_STP g_cat⁻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.