Ni–In Synergy in CO(2) Hydrogenation to Methanol

[Image: see text] Indium oxide (In(2)O(3)) is a promising catalyst for selective CH(3)OH synthesis from CO(2) but displays insufficient activity at low reaction temperatures. By screening a range of promoters (Co, Ni, Cu, and Pd) in combination with In(2)O(3) using flame spray pyrolysis (FSP) synthesis, Ni is identified as the most suitable first-row transition-metal promoter with similar performance as Pd–In(2)O(3). NiO–In(2)O(3) was optimized by varying the Ni/In ratio using FSP. The resulting catalysts including In(2)O(3) and NiO end members have similar high specific surface areas and morphology. The main products of CO(2) hydrogenation are CH(3)OH and CO with CH(4) being only observed at high NiO loading (≥75 wt %). The highest CH(3)OH rate (∼0.25 g(MeOH)/(g(cat) h), 250 °C, and 30 bar) is obtained for a NiO loading of 6 wt %. Characterization of the as-prepared catalysts reveals a strong interaction between Ni cations and In(2)O(3) at low NiO loading (≤6 wt %). H(2)-TPR points to a higher surface density of oxygen vacancy (O(v)) due to Ni substitution. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electron paramagnetic resonance analysis of the used catalysts suggest that Ni cations can be reduced to Ni as single atoms and very small clusters during CO(2) hydrogenation. Supportive density functional theory calculations indicate that Ni promotion of CH(3)OH synthesis from CO(2) is mainly due to low-barrier H(2) dissociation on the reduced Ni surface species, facilitating hydrogenation of adsorbed CO(2) on O(v).