Enhancing CO ₂ Hydrogenation to Methanol over In ³⁺ -Doped ZnCo ₂ O ₄ Spinel Catalysts

Cobalt-based spinel catalysts, featuring an ordered arrangement of Co2+ and Co3+ in tetrahedral and octahedral sites, respectively, possess adjustable structural and electronic properties and superior CO2 adsorption capacity, which profoundly achieve a maximum CO2 conversion. However, low methanol selectivity for CO2 hydrogenation remains a grand challenge for cobalt-based spinel catalysts. To this end, heteroatom doping in Co-based spinel catalysts, particularly with In3+, was novelly designed to enhance both CO2 conversion and methanol selectivity concurrently by modulating these properties. Here, ZnCo2O4 spinel catalysts with varying indium doping levels were synthesized via coprecipitation and evaluated for CO2 hydrogenation to methanol. The results demonstrate that increasing In3+ content reduced methane selectivity and enhanced methanol selectivity, with a slight decrease in CO2 conversion. The Co–Zn–In20% catalyst exhibited optimal performance, achieving 14.7% CO2 conversion, 90% methanol selectivity, and a space–time yield of 0.75 gMeOH·gcat–1·h–1 under the condition (5.0 MPa, 270 °C, GHSV = 24,000 mL·gcat–1·h–1 and H2/CO2 = 4). In situ DRIFTS analysis, combined with structural characterization, indicates that indium doping introduced lattice defects and oxygen vacancies, weakened Co–O bonds, and promoted intermediate desorption, thereby suppressing the formation of metallic Co and facilitating methanol production via the formate pathway. It is expected that indium doping can be extensively employed as a general strategy to substantially promote selective methanol synthesis in various catalysts with high CO2 conversion.