In order to reduce anthropogenic CO₂ emissions, the identification of routes in which carbon dioxide can be utilized as a chemical feedstock is a highly sought goal in the scientific community. One attractive approach comprises its hydrogenation to methanol, which serves as a fuel and a starting material for the manufacture of a multitude of chemicals. So far, only one commercial process for CO₂-based methanol production has been developed (Carbon Recycling International, 5 million liters in 2015),¹ since most of the heterogeneous catalysts investigated suffer from limited selectivity, mainly due to the competitive reverse water gas shift reaction, and/or short lifetime. Recently, we have introduced indium oxide (9 wt.%) supported on zirconia as a highly selective and extraordinarily stable material for this transformation.² In that study, we gathered evidence that the electronic interaction between the carrier and the active phase as well as the reaction conditions play a crucial role in the formation of selective active sites, i.e., surface oxygen vacancies. Here, we aim at achieving a deeper understanding of this catalyst to improve its methanol space time yield. In order to vary the distribution and degree of contact between In₂O₃ and ZrO₂, we applied various preparation methods, i.e., wet impregnation, spray deposition, ball milling, hydrothermal synthesis, and co-precipitation. Preliminary tests under industrially-relevant temperature and pressure conditions showed that the first two protocols produce superior catalysts (Figure 1). Since XRD indicated that the particle size of In₂O₃ is smaller in these solids, we are currently producing additional materials with variable In content to tune the dimensions of the In₂O₃ crystallites. Characterization through a battery of state-of-the-art techniques will be coupled to the catalytic assessment to establish structure-performance relations and attain even more efficient materials.

Figure 1 Space time yield (STY) of methanol in the direct hydrogenation of CO₂ over In₂O₃-ZrO₂ catalysts prepared by different synthesis methods.

[1] http://carbonrecycling.is/george-olah/2016/2/14/worlds-largest-co2-methanol-plant
[2] O. Martin, A. J. Martín, C. Mondelli, S. Mitchell, T. F. Segawa, R. Hauert, C. Drouilly, D. Curulla-Ferré, J. Pérez-Ramírez, Angew. Chem. Int. Ed. 2016, 55, 6261.