Synthesis modification of hydroxyapatite surface for ethanol conversion: The role of the acidic/basic sites ratio.

[Display omitted] • Ultrasound, microwave and autoclave were tested in the synthesis of hydroxyapatite. • The post-synthesis treatments changed the acid/basic profile on the solid surface. • The microwave-treated catalyst had the best results in the ethanol condensation. • Basic surface sites decreased intrinsic activation energies. • Balanced distribution of acidic/basic sites accelerates aldol condensation. Several studies have investigated the acidic/basic sites of the hydroxyapatite (HAP) surface. However, their specific role in the catalytic properties of HAP is still discussed. Here, we investigated different preparation methods (ultrasound, microwave, and autoclave) of HAP and how they affect the catalytic activity for ethanol conversion. The synthesis methods changed the number and distribution of acidic/basic sites, affecting the product selectivity. The best performance toward condensation products was observed for the microwave-treated catalyst. We also report a density functional theory (DFT) investigation on the reaction pathways of twelve steps of ethanol conversion on the HAP(0001) surface. Our DFT results suggest that the availability of basic sites can facilitate acetaldehyde formation. Furthermore, our theoretical insights indicate that the balance of acidic/basic sites contributes to the C−C bond formation, which is consistent with our experimental observations. [ABSTRACT FROM AUTHOR]