Ni-In Synergy in CO Hydrogenation to Methanol.

Indium oxide (InO) is a promising catalyst for selective CHOH synthesis from CO but displays insufficient activity at low reaction temperatures. By screening a range of promoters (Co, Ni, Cu, and Pd) in combination with InO using flame spray pyrolysis (FSP) synthesis, Ni is identified as the most suitable first-row transition-metal promoter with similar performance as Pd-InO. NiO-InO was optimized by varying the Ni/In ratio using FSP. The resulting catalysts including InO and NiO end members have similar high specific surface areas and morphology. The main products of CO hydrogenation are CHOH and CO with CH being only observed at high NiO loading (≥75 wt %). The highest CHOH rate (∼0.25 g/(g 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 InO at low NiO loading (≤6 wt %). H-TPR points to a higher surface density of oxygen vacancy (O) 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 hydrogenation. Supportive density functional theory calculations indicate that Ni promotion of CHOH synthesis from CO is mainly due to low-barrier H dissociation on the reduced Ni surface species, facilitating hydrogenation of adsorbed CO on O.