Enhancing the catalytic performance of Cu/ZnO/Al₂O₃ catalyst in methanol synthesis from biomass-derived syngas with CeO₂, MnO₂ and ZrO₂ as promoters

The performance of Cu/ZnO/Al₂O₃ (CZA) catalysts promoted by addition of CeO₂, MnO₂ or ZrO₂ in direct methanol production from unconventional syngas was experimentally investigated. The unconventional syngas used in this study contain 25% H₂, 25% CO, 20% CH₄, 20% CO₂ and 10% N₂, representing biomass-derived syngas cultivated from an industrial wood chips pyrolysis plant. The catalysts were synthesised using co-precipitation technique and tested for methanol synthesis in a fixed-bed reactor. The activity test of the catalysts showed that the addition of CeO₂ or ZrO₂ to the CZA catalyst improved the methanol yield, albeit with lower selectivity, whereas adding MnO₂ enhanced methanol selectivity but decreased the methanol yield. ZrO₂-promoted catalyst showed the best-improved activity and stability. The calcined and spent catalysts were characterised using X-ray diffraction (XRD), N₂ physisorption, N₂O chemisorption, hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The characterisation results indicate that the catalytic activity is dependent on Cu dispersion, Cu-active surface area, the catalyst reducibility, Brunauer–Emmett–Teller (BET) surface area and the Cu⁰/Cu⁺ ratio. In contrast, catalyst stability was related to the proportion of Cu⁺ among all surface Cu species.