Tailored support reduction of Cu/SrTiO3 catalysts for enhanced methanol production†

Abstract

Copper supported on strontium titanate is explored as a catalyst in the hydrogenation of carbon dioxide to methanol. We used combined H₂-TPR, O₂-TPO, XPS, and STEM-EDX to identify the support defects, tailored by the activation procedure. Strontium titanate forms oxygen vacancies under high-temperature reductive treatments. The extent of its reduction is a function of the copper content and of the pressure; the highest extent is achieved at 2 wt% copper and 20 bar hydrogen. The catalytic data agree with a direct relationship between the methanol selectivity and the concentration of the oxygen vacancies, with the best results being: 90% (10% towards carbon monoxide) and an associated methanol space time yield of 0.49 g_MeOH g_cat⁻¹ h⁻¹. The selectivity is higher than that achieved on a typical copper catalyst on zinc oxide alumina, while keeping the competitive productivity value, despite having thirty times lower copper content. Post-reaction characterisation suggests that these sites are stable under reaction conditions. We propose a dual-site surface mechanism based on oxygen vacancies formed at the copper–support interface and via long-distance hydrogen spillover.