Ni–In Synergy in CO₂ Hydrogenation to Methanol

Abstract

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 .

Advances in studies of the structural effects of supported Ni catalysts for CO2hydrogenation: from nanoparticle to single atom catalyst

“…158–160 In 2 O 3 supported Ni-SACs were theoretically confirmed to be active for RWGS as well. 29,161 This can be further confirmed by the effect of the reaction temperature on the stability of the supported Ni-SAC. 35 It was reported that the MgO supported Ni-SAC remains stable at a reaction temperature of 300 °C, with which CO is produced through the RWGS reaction.…”

“…However, the nickel atom numbers have a big influence. Ni 1 /In 2 O 3 and Ni 2 /In 2 O 3 catalysts favour the RWGS reaction, 29,161 leading to CO formation, because of higher energy barriers for methanol synthesis.…”

“…35 The location of the Ni-SAC on In 2 O 3 has significant effects on hydrogen dissociation as well for CO 2 hydrogenation. 29 For the stoichiometric In 2 O 3 surface and the In 2 O 3 (111) surface doped with a Ni single atom, H 2 dissociation leads to two OH groups. This indicates a homolytic dissociation.…”

“…A change in the electronic structure can cause a big change in the selectivity. 26–35 One can shift the selectivity of CO 2 hydrogenation from selective production of methane to methanol or CO or even formic acid by the change of the catalyst structure. The electronic structure of a supported Ni catalyst can be tuned by the physical structure and components, including the supporting material, of the catalyst.…”

An indium-induced-synthesis In0.17Ru0.83O2 nanoribbon as highly active electrocatalyst for oxygen evolution in acidic media at high current densities above 400 mA cm−2

“…Moreover, an appropriate band structure for semiconductors can effectively regulate the electronic structure of the reactive site. 30–35 Herein, indium doping was adopted to regulate the d-band center of the metal active site to enhance catalytic capacity. Furthermore, the reduction of the work function increases the electron transfer capacity between the reactants and the catalyst surface, 36 which is also conducive to the electrocatalytic process.…”