Surface chemistry of hydroxyapatite for sustainable n-butanol production from bio-ethanol
Daniyal Kiani, Jonas Baltrušaitis
Abstract
Calcium hydroxyapatite (HAp) has emerged as a green, bifunctional catalyst for the heterogeneous coupling of various biomass-derived molecules, including ethanol to n-butanol via the Guerbet reaction. This review critically analyzes the surface chemistry of HAp catalysts based on the available temporally- and spatially-resolved in situ and operando spectroscopic studies. Specifically, the nature of the isolated acidic and basic surface sites, as well as the acid-base pairs, is elucidated based on chemical probe spectroscopy results. Surface structure-reactivity relationships are also rationalized based on the nature and identity of the surface sites involved in various steps of the Guerbet reaction to produce n-butanol over the HAp catalysts. Finally, future directions in experimental investigations are suggested to guide the rational design of improved HAp-based catalysts for the Guerbet reaction and other similar chemistries.