Hydrogenation of carbon dioxide to methanol over palladium-promoted Cu/ZnO/A12O3 catalysts

The effect of Pd on a Cu/ZnO/A1₂O₃ catalyst for methanol synthesis from CO₂/H₂ has been investigated. Activities of impregnated catalysts and physical mixtures were studied in an internal recycle reactor under 5 MPa, 250°C and a range of conversions. In all cases, the promotion of methanol production was greater at higher flow rates (lower conversions). The promotion achieved by use of Pd/A1₂O₃+ Cu/ZnO/Al₂O₃ physical mixtures was found to increase with Pd content. Greater promotion was observed over the Pd impregnated Cu/ZnO/Al₂O₃ catalysts, although this was insensitive to the particular Pd loadings used. The results are consistent with the proposal that hydrogen spillover is responsible for the observed promotion. The effectiveness of Pd as a promoter for the reduction of CuO in the catalysts was studied by TPR and was found to be related to the level of promotion in methanol production.