Construction of Ni/In 2 O 3 Integrated Nanocatalysts Based on MIL-68(In) Precursors for Efficient CO 2 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/In2 O3 nanocatalysts by using porous MIL-68(In) and nickel(II) acetylacetonate (Ni(acac)2 ) as the dual precursors of In2 O3 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 In2 O3 support and inhibited the metal sintering at high temperatures. The varied catalyst fabrication parameters were explored, indicating that the designed Ni/In2 O3 catalyst (Ni content of 5 wt %) exhibited better catalytic performance than the compared catalyst prepared using In(OH)3 as a precursor of In2 O3 . The obtained Ni/In2 O3 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 In2 O3 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/In2 O3 catalyst predominantly follows the formate pathway in the CO2 hydrogenation to methanol, with HCOO* and *H3 CO 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/In2 O3 nanocatalyst fabricated using metal-organic frameworks as precursors can effectively promote CO2 thermal hydrogenation to methanol.