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.

Two sets of silica-supported nickel phosphide catalysts with a nickel content of about 2.5 and 10 wt % and Ni/P molar ratio 2/1, 1/1 and 1/2 in each set, were prepared by way of a temperature-programmed reduction method using (Ni(CH 3 COO) 2 ) and ((NH 4 ) 2 HPO 4 ) as a precursor. The Ni x P y /SiO 2 catalysts were characterized using chemical analysis N 2 physisorption, XRD, TEM, 31 P MAS NMR. Methyl palmitate hydrodeoxygenation (HDO) was performed in a trickle-bed reactor at 3 MPa and 290 • C with LHSV ranging from 0.3 to 16 h −1 . The Ni/P ratio was found to affect the nickel phosphide phase composition, PO x groups content and catalytic properties in methyl palmitate HDO with the TOF increased along with a decline of Ni/P ratio and a growth of PO x groups' content. Taking into account the possible routes of methyl palmitate conversion (metal-catalyzed hydrogenolysis or acid-catalyzed hydrolysis), we proposed that the enhancement of acid PO x groups' content with the Ni/P ratio decrease provides an enhancement of the rate of methyl palmitate conversion through the acceleration of acid-catalyzed hydrolysis.

The effect of support nature, SiO2 and γ-Al2O3, on physicochemical and catalytic properties of nickel phosphide catalysts in methyl palmitate hydrodeoxygenation (HDO) has been considered. Firstly, alumina-supported nickel phosphide catalysts prepared by temperature-programmed reduction method starting from different precursors (phosphate–Ni(NO3)2 and (NH4)2HPO4 or phosphite–Ni(OH)2 and H3PO3) were compared using elemental analysis, N2 physisorption, H2-TPR, XRD, TEM, NH3-TPD, 27Al and 31P MAS NMR techniques and catalytic experiments. The mixture of nickel phosphide phases was produced from phosphate precursor on alumina while using of phosphite precursor provides Ni2P formation with the higher activity in methyl palmitate HDO. Besides, the comparative study of the performances of Ni2P/SiO2 and Ni2P/Al2O3 catalysts demonstrates the apparent superiority of alumina-supported Ni2P in the methyl palmitate hydrodeoxygenation. Considering the tentative scheme of methyl palmitate transformation, we proposed that cooperation of Ni2P and acid sites on the surface of alumina provides the enhanced activity of alumina-supported Ni2P through the acceleration of acid-catalysed hydrolysis.

Abstract:The Ni 2 P/SiO 2 catalyst, which was prepared by in situ temperature-programmed reduction and in the mixture with the inert (SiC, SiO 2 ) or acidic (γ-Al 2 O 3 ) material was studied in methyl palmitate hydrodeoxygenation (HDO). Methyl palmitate HDO was carried out at temperatures of 270-330 • C, H 2 /feed volume ratio of 600 Nm 3 /m 3 , and H 2 pressure of 3.0 MPa. Ni 2 P/SiO 2 catalyst, diluted with γ-Al 2 O 3 showed a higher activity than Ni 2 P/SiO 2 catalyst diluted with SiC or SiO 2 . The conversion of methyl palmitate increased significantly in the presence of γ-Al 2 O 3 most probably due to the acceleration of the acid-catalyzed reaction of ester hydrolysis. The synergism of Ni 2 P/SiO 2 and γ-Al 2 O 3 in methyl palmitate HDO can be explained by the cooperation of the metal sites of Ni 2 P/SiO 2 and the acid sites of γ-Al 2 O 3 in consecutive metal-catalyzed and acid-catalyzed reactions of HDO. The obtained results let us conclude that the balancing of metal and acid sites plays an important role in the development of the efficient catalyst for the HDO of fatty acid esters over supported phosphide catalysts.