Despite the fact that metastable aluminum oxides are actively used in industry, there is a discrepancy in the literature regarding their crystal structure. All this leads to difficulties in data interpretation and, as a consequence, classification problems. This work is aimed at solving these tasks. The main features of powder X-ray diffraction of typical samples of three Al₂O₃ polymorphs (γ-, χ-, η-) are analyzed. Specifics and fundamental differences in X-ray scattering and their relationship with the structural organization at the nanostructure level are clearly shown. The work demonstrates the possibilities of analyzing experimental powder X-ray diffraction data using a modern approach based on the Debye Scattering Equation for studying the organization of such complex systems.

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(CH₃COO)₂) and ((NH₄)₂HPO₄) as a precursor. The Ni_xP_y/SiO₂ catalysts were characterized using chemical analysis N₂ physisorption, XRD, TEM, ³¹P 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.

The Ni₂P/SiO₂ catalyst, which was prepared by in situ temperature-programmed reduction and in the mixture with the inert (SiC, SiO₂) or acidic (γ-Al₂O₃) material was studied in methyl palmitate hydrodeoxygenation (HDO). Methyl palmitate HDO was carried out at temperatures of 270–330 °C, H₂/feed volume ratio of 600 Nm³/m³, and H₂ pressure of 3.0 MPa. Ni₂P/SiO₂ catalyst, diluted with γ-Al₂O₃ showed a higher activity than Ni₂P/SiO₂ catalyst diluted with SiC or SiO₂. The conversion of methyl palmitate increased significantly in the presence of γ-Al₂O₃ most probably due to the acceleration of the acid-catalyzed reaction of ester hydrolysis. The synergism of Ni₂P/SiO₂ and γ-Al₂O₃ in methyl palmitate HDO can be explained by the cooperation of the metal sites of Ni₂P/SiO₂ and the acid sites of γ-Al₂O₃ 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.