Ni–In Synergy in CO₂ Hydrogenation to Methanol

High Resolution Image Download MS PowerPoint Slide 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 .