Al Promotion of In 2 O 3 for CO 2 Hydrogenation to Methanol.

In 2 O 3 is a promising catalyst for the hydrogenation of CO 2 to methanol, relevant to renewable energy storage in chemicals. Herein, we investigated the promoting role of Al on In 2 O 3 using flame spray pyrolysis to prepare a series of In 2 O 3 -Al 2 O 3 samples in a single step (0-20 mol % Al). Al promoted the methanol yield, with an optimum being observed at an Al content of 5 mol %. Extensive characterization showed that Al can dope into the In 2 O 3 lattice (maximum ∼ 1.2 mol %), leading to the formation of more oxygen vacancies involved in CO 2 adsorption and methanol formation. The rest of Al is present as small Al 2 O 3 domains at the In 2 O 3 surface, blocking the active sites for CO 2 hydrogenation and contributing to higher CO selectivity. At higher Al content (≥10 mol % Al), the particle size of In 2 O 3 decreases due to the stabilizing effect of Al 2 O 3 . Nevertheless, these smaller particles are prone to sintering during CO 2 hydrogenation since they appear to be more easily reduced. These findings show subtle effects of a structural promoter such as Al on the reducibility and texture of In 2 O 3 as a CO 2 hydrogenation catalyst.