Cu/ZnO catalysts integrated with Al2O3 and/or SiO2 for methanol synthesis: Deciphering the additive-induced boost in catalytic performance by XAFS

Abstract

The development of active, long-lived methanol synthesis catalysts can be expedited by thoroughly understanding the operating mechanisms of promoter additives. SiO₂ serves as an effective support and promoter for Cu/ZnO-type methanol synthesis catalysts; however, it has not been studied as extensively as the industrially predominant Al₂O₃, despite being similarly potent. Therefore, we conducted X-ray absorption fine structure studies to probe the effects of incorporating Al₂O₃ and SiO₂ additives into Cu/ZnO-based heterogeneous catalysts. The results revealed that the additive elements primarily affected the ability of the Zn species to generate oxygen vacancies by distorting the local structure around element-doped ZnO and that the number of oxygen vacancies correlated to the catalytic activity. Additionally, the oxygen vacancies in ZnO in the Al/Si-incorporated catalysts diminished under catalytic reaction conditions, thereby providing information on the deactivation of catalytic reactions. Our findings can facilitate the development of highly active industrial-grade methanol synthesis catalysts.