Effect of precursor on the catalytic properties of Ni2P/SiO2 in methyl palmitate hydrodeoxygenation

Abstract

The effect of phosphorus precursor on the physicochemical and catalytic properties of silica-supported nickel phosphide catalysts in the hydrodeoxygenation (HDO) of aliphatic model compound methyl palmitate (C₁₅H₃₁COOCH₃) has been considered. Nickel acetate (Ni(OAc)₂) and diammonium hydrogen phosphate ((NH₄)₂HPO₄) (phosphate precursor) or nickel hydroxide (Ni(OH)₂) and phosphorous acid (H₃PO₃) (phosphite precursor) have been used for the catalyst preparation by incipient wetness impregnation of SiO₂ with an aqueous solution of the precursors, followed by temperature-programmed reduction in hydrogen flow. Chemical analysis (ICP-AES), H₂-TPR, NH₃-TPD, ³¹P MAS NMR, XRD, and TEM have been employed for the characterization of the catalysts. The optimal reduction parameters of the silica-supported nickel phosphide catalysts have been found for the phosphate and phosphite precursors in terms of their activity in methyl palmitate HDO. The Ni₂P/SiO₂ catalysts prepared by the phosphite method have shown higher catalytic activity in comparison with the Ni₂P/SiO₂ catalysts prepared by the phosphate method. The activity has been shown to depend on the catalyst handling after reduction: in situ reduced catalysts demonstrate higher conversion of methyl palmitate than the samples exposed to the reduction, passivation and re-reduction steps.