Spinel Nanostructures for the Hydrogenation of CO₂ to Methanol and Hydrocarbon Chemicals

Abstract

Composite oxides have been widely applied in the hydrogenation of CO/CO₂ to methanol or as the component of bifunctional oxide-zeolite for the synthesis of hydrocarbon chemicals. However, it is still challenging to disentangle the stepwise formation mechanism of CH₃OH at working conditions and selectively convert CO₂ to hydrocarbon chemicals with narrow distribution. Here, we investigate the reaction network of the hydrogenation of CO₂ to methanol over a series of spinel oxides (AB₂O₄), among which the Zn-based nanostructures offer superior performance in methanol synthesis. Through a series of (quasi) in situ spectroscopic characterizations, we evidence that the dissociation of H₂ tends to follow a heterolytic pathway and that hydrogenation ability can be regulated by the combination of Zn with Ga or Al. The coordinatively unsaturated metal sites over ZnAl₂O_<i>x</i> and ZnGa₂O_<i>x</i> originating from oxygen vacancies (OVs) are evidenced to be responsible for the dissociative adsorption and activation of CO₂. The evolution of the reaction intermediates, including both carbonaceous and hydrogen species at high temperatures and pressures over the spinel oxides, has been experimentally elaborated at the atomic level. With the integration of a series of zeolites or zeotypes, high selectivities of hydrocarbon chemicals with narrow distributions can be directly produced from CO₂ and H₂, offering a promising route for CO₂ utilization.