Hydroxyapatite-based materials as catalysts: A review

Abstract

Hydroxyapatite, a bioceramic material, possesses sufficient stability in aqueous and organic medium and it is mainly known for its role in tooth and bone structure. However, it is less-known that, in certain conditions, the HA can be used as a catalyst in its free, metal-doped and composite forms. HA as a catalyst is generally prepared by i mpregnation or co-precipitation methods, sometimes from natural P-containing wastes. HA can be doped with mono- or polymetallic ions or nanoparticles and can contain other admixtures or supports (i.e., carbon). Different Ca/P ratios (ideal 1.67; the ranges are 1.5–1.7 in synthetic and 1.5–1.8 in biologic forms) can be revealed for the HA. Nanosized HA forms are frequent in several applications. A variety of distinct processes can be HA-catalyzed, such as oxidation of alcohols, dehydrogenation, hydrogenation and hydrogenolysis, C-C bond formation, among other important existing low- and large-scale organic processes. The HA can be also used for catalytic environmental remediation, CO₂ fixation, and N₂O decomposition. In this review, we emphasize most recent advances (mainly last decade) on the catalytic HA applications, except for biomedical ones.