Construction of Ni/In2O3 Integrated Nanocatalysts Based on MIL-68(In) Precursors for Efficient CO2 Hydrogenation to Methanol

The efficient and economic conversion of CO₂ and renewable H₂ into methanol has received intensive attention due to growing concern for anthropogenic CO₂ emissions, particularly from fossil fuel combustion. Herein, we have developed a novel method for preparing Ni/In₂O₃ nanocatalysts by using porous MIL-68(In) and nickel(II) acetylacetonate (Ni(acac)₂) as the dual precursors of In₂O₃ and Ni components, respectively. Combined with in-depth characterization analysis, it was revealed that the utilization of MIL-68(In) as precursors favored the good distribution of Ni nanoparticles (∼6.2 nm) on the porous In₂O₃ support and inhibited the metal sintering at high temperatures. The varied catalyst fabrication parameters were explored, indicating that the designed Ni/In₂O₃ catalyst (Ni content of 5 wt %) exhibited better catalytic performance than the compared catalyst prepared using In(OH)₃ as a precursor of In₂O₃. The obtained Ni/In₂O₃ catalyst also showed excellent durability in long-term tests (120 h). However, a high Ni loading (31 wt %) would result in the formation of the Ni-In alloy phase during the CO₂ hydrogenation which favored CO formation with selectivity as high as 69%. This phenomenon is more obvious if Ni and In₂O₃ had a strong interaction, depending on the catalyst fabrication methods. In addition, with the aid of in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory (DFT) calculations, the Ni/In₂O₃ catalyst predominantly follows the formate pathway in the CO₂ hydrogenation to methanol, with HCOO* and *H₃CO as the major intermediates, while the small size of Ni particles is beneficial to the formation of formate species based on DFT calculation. This study suggests that the Ni/In₂O₃ nanocatalyst fabricated using metal-organic frameworks as precursors can effectively promote CO₂ thermal hydrogenation to methanol.