The effect of metal additives in Cu/Zn/Al2O3 as a catalyst for low-pressure methanol synthesis in an oil-cooled annulus reactor

The effect of metal additives, including Zr, Mg, and Ga, on the conventional Cu/ZnO/Al2O3 (CZA) catalyst, was investigated for methanol synthesis using an oil-cooled annulus reactor. The annulus reactor was found to reduce the temperature gradient within the diluted catalyst bed by effective cooling and thus provide experimental data at steady-state and in kinetic regime allowing for the comparison of intrinsic activity between different catalysts. The addition of Zr enhanced the overall performance of methanol synthesis. However, the CZA-Zr catalyst displayed significantly reduced CO2 conversion, possibly due to intensified water-gas shift reaction activity. The addition of Ga and Mg to CZA was found to be detrimental to the catalytic performance and is attributed to difficulties in reducibility and the increased crystalline size of copper particles. A relatively long induction period was observed for CZA-Zr sample in this study, which is attributed to the effective cooling imparted by the annulus reactor suppressing the r-WGS reaction.