β-tricalcium phosphates doped with transition metals for biofuel additives through glycerol valorization: On the effects of the metal contents

•Cu, Ni or Co-doped tricalcium phosphates by a solid state reaction.•β-TCP phase found in all solids for metal doping varying from 9 to 17 wt.%.•Effects of Ca2+ ions replacement by acidic Cu2+ into the TCPs lattice.•The surface Cu2+/Cu+ ions out of the TCP matrix altering the defect equilibrium.•Actives in the glycerol acetylation for valuable glycerol esters such as triacetin. Nanosized calcium phosphates doped with transition metals (TCPs) were examined in the acetylation of glycerol for the biofuel additives production. The effects of transition metal (Cu, Co or Ni) contents on the catalytic performances were also investigated. The Co and Ni-doped TCPs had the metal included in their structures showing β-TCP, as the main phase found in all solids. Doping the TCPs down to 12 wt.% resulted in the inclusion of copper or cobalt in the TCPs matrix. Such structure provided high density acid surface active sites for converting glycerol toward its acetylation with acetic acid reaction compared to Co and Ni-TCPs counterparts. Morphological features revealed typical rod-shaped particles, depending on the doping level. Substitutions of Ca2+ for acidic Cu2+ ions into the TCPs lattice, especially for high Cu contents, produced surface Cu2+/Cu+ ions outside the TCP matrix. This altered the defect equilibrium of the TCP providing a significant performance for glycerol conversion of ca. 55 % and triacetin selectivity of 39 % in four cycles of uses. [Display omitted]