Improved catalytic activity and stability of Cu/ZnO catalyst by boron oxide modification for low-temperature methanol synthesis

Abstract

Surface modification is an efficient way for enhanced activity and stability in methanol synthesis over traditional Cu/ZnO catalyst. However, previous investigations mainly focused on different metal oxides or pure metals as additives to modify Cu-based catalysts. The influence of non-metal oxide incorporation on the catalytic activity and stability of Cu/ZnO catalyst lacks a deep study. In this work, we prepared a series of boron oxide (B2O3) modified Cu/ZnO catalysts (CZB-R-x) with tunable boron content to disclose the role of B2O3. With the increase of B/Cu molar ratio (x) from 0 to 0.10, there exists a volcano-shaped correlation between catalytic activity and B/Cu molar ratio, revealing a balance between the promotional effect of B2O3 and the negative influence caused by excessive B2O3. CZB-R-0.05 catalyst can increase methanol space time yield (STY) by 7.5 times and total carbon turnover frequency (TOF) by 5.8 times at 170 °C, when compared to unmodified Cu/ZnO, and also stabilizes for 700 h at 200 °C without obvious deactivation. Kinetic studies indicate that the apparent activation energy required for low-temperature methanol synthesis is remarkably decreased from 217.2 kJ/mol over Cu/ZnO to 121.4 kJ/mol over CZB-R-0.05. Importantly, STY of methanol correlates linearly with Cu0 surface area and the number of strongly acidic sites, suggesting that higher Cu0 surface area and stronger surface acidity are key prerequisites for achieving outstanding performance for low-temperature methanol synthesis.