Ultra-small Au nanocluster supported on modified mesoporous hydroxyapatite for base-free oxidative esterification of alcohols

The oxidative esterification of alcohols is a key transformation in fine chemical synthesis and green chemistry. However, supported Au catalysts often suffer from nanoparticle agglomeration, leading to a significant loss of activity. Here, we report that Zn-doped hydroxyapatite (ZnHAP) can effectively stabilize ultra-small Au nanoclusters through Au-support interactions, even after high-temperature calcination at 400 ℃. The resulting Au/ZnHAP catalyst, with an ultralow Au loading of 0.25 wt%, exhibits outstanding performance in the base-free oxidative esterification of benzyl alcohol (Conv. 99%, Sele. 95%). Mechanistic investigations reveal that Zn incorporation into HAP modulates the surface basicity, thereby enhancing substrate adsorption and accelerating the key oxidative dehydrogenation step of the hemiacetal intermediate. Moreover, the increased Au 0 fraction induced by higher calcination temperatures further promotes benzyl alcohol activation. Consequently, under base-free conditions, the ester formation rate is governed by both the number of exposed Au active sites and the balanced distribution of surface acid–base sites. This work provides new mechanistic insights and practical guidance for the rational design of efficient, base-free oxidative esterification catalysts based on supported Au systems.