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 Co 2+ and Co 3+ in tetrahedral and octahedral sites, respectively, possess adjustable structural and electronic properties and superior CO 2 adsorption capacity, which profoundly achieve a maximum CO 2 conversion. However, low methanol selectivity for CO 2 hydrogenation remains a grand challenge for cobalt-based spinel catalysts. To this end, heteroatom doping in Co-based spinel catalysts, particularly with In 3+, was novelly designed to enhance both CO 2 conversion and methanol selectivity concurrently by modulating these properties. Here, ZnCo 2 O 4 spinel catalysts with varying indium doping levels were synthesized via coprecipitation and evaluated for CO 2 hydrogenation to methanol. The results demonstrate that increasing In 3+ content reduced methane selectivity and enhanced methanol selectivity, with a slight decrease in CO 2 conversion. The Co–Zn–In20% catalyst exhibited optimal performance, achieving 14.7% CO 2 conversion, 90% methanol selectivity, and a space–time yield of 0.75 g MeOH ·g cat –1 ·h –1 under the condition (5.0 MPa, 270 °C, GHSV = 24,000 mL·g cat –1 ·h –1 and H 2 /CO 2 = 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 CO 2 conversion.