Route-dependent Cu–Zn/γ-Al2O3 catalysts for efficient CO2 hydrogenation to methanol

The direct hydrogenation of CO2 to methanol is widely recognized as a key route within carbon-capture-and-utilization strategies; however, its efficiency remains strongly limited by CO2 thermodynamic stability and the scarcity of catalysts that simultaneously ensure high dispersion, stable Cu-ZnOx interfaces, and optimized textural accessibility. Although numerous studies have explored Cu–ZnO–Al2O3 systems, the open literature lacks a route-resolved understanding of how different impregnation pathways reshape the mesoporous γ-Al2O3 support and, consequently, the structure-activity relationship under identical synthesis and reaction conditions. This study fills this gap by systematically comparing two industrially relevant impregnation routes (R1 and R2) applied to the same γ-Al2O3 support while maintaining constant Cu/Zn loading, calcination protocol, and micro-plant operation parameters. Characterization such as BET, BJH, XRD, STEM-EDX reveals that the R1 pathway preserves higher surface area and pore accessibility, enabling finer Cu-ZnOx dispersion, whereas the R2 route promotes partial pore blockage and larger aggregated crystallites. Catalytic tests performed at 240 °C, 30 bar, and H2/CO2 = 3 demonstrate a strong route-dependent performance enhancement. The Cu-R1 catalyst exhibited limited activity, reaching only 10.2% CO2 conversion and 8.6% methanol selectivity, whereas Zn incorporation significantly improved catalytic performance. The Zn/Cu-R1 catalyst achieved 19.6% conversion, 34% selectivity, 6.7% methanol yield, and 61.1 g(CH3OH)/kg(cat)h productivity after 10 h of operation. Despite its high selectivity (35.7%), Zn/Cu-R2 delivered a lower yield (5%) due to reduced CO2 conversion (14%), confirming that pore-accessible Cu-ZnOx interfacial dispersion is the primary determinant of methanol productivity. The establishment of links between impregnation history, pore restructuring, Cu/Zn dilution, and methanol production metrics, this work defines a clear scientific role in catalyst engineering and provides mechanistic guidelines for designing next-generation Cu–Zn/γ-Al2O3 catalysts for sustainable hydrogen-based methanol synthesis.

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