Hydrodeoxygenation Of Anisole Over Supported Phosphide Catalysts

Supported phosphide catalysts were prepared by the temperature-programmedreduction （TPR） method. The influences of Ni/Mo molar ratio, support property, Ni/Pmolar ratio and metal oxide promoters on their structures and catalytic performancesfor the hydrodeoxygenation（HDO） of anisole were investigated by means of H₂-TPR,UV-Vis DRS, N2adsorption-desorption, XRD, CO chemisorption, TPD, XPS, TPH,TEM, SEM, and reactivity evaluation. The deactivation of nickel phosphide catalystswas also explored.SiO₂-supported phosphide catalysts with different Ni/Mo molar ratios wereprepared at650oC. The reducibility of precursors and the dispersion of phosphideswere promoted via co-existence of nickel and molybdenum species. Since there wasstrong interaction between γ-Al₂O₃and P species in the γ-Al₂O₃-supported phosphateprecursors, the formation of phosphide was inhibited. In phosphides, metal sites(Ni^δ+（0<δ<1） and Mo^δ+（0<δ<4）) possess both metallicity and Lewis acidity, whileP-OH groups present Br nsted acidity. During the HDO of anisole, metal sites andP-OH groups were all active for demethylation, hydrogenation and deoxygenation. Incomparison with Mo^δ+sites and P-OH groups, Ni^δ+sites showed the best HDOperformance. No synergism between the Ni^δ+and Mo^δ+sites exists during the HDO ofanisole. Lewis acid sites related to γ-Al₂O₃were active for demethylation andmethyltransfer, while metal sites (especially Ni^δ+) inhibited the methyltransfer.Compared to γ-Al₂O₃, SiO₂-supported phosphide catalysts presented better stability.With the decrease of Ni/P molar ratio, the reducibility of SiO₂-supported nickelphosphates became difficult, and the formed phases were Ni₃P, Ni₁₂P₅and Ni₂P insequence. Also, the decrease of Ni/P molar ratio resulted in the decrease of surfaceareas and CO uptakes of nickel phosphide catalysts. The Ni^δ+sites with higherelectron density showed higher activity for HDO. To investigate the roles of Ni^δ+sitesand P-OH groups, the hydrogenation of benzene and the HDO of cyclohexanol onNi/SiO₂, Ni₃P/SiO₂, and Ni₂P/SiO₂were also tested. The results show that the Ni^δ+sites with higher electron density presented higher hydrogenation activity, while theyhad lower stability. In the HDO of cyclohexanol, P-OH groups and Ni^δ+sitescatalyzed the dehydration and the hydrogenation, respectively.The catalyst deactivation was related to the oxidation caused by H₂O and the carbonous deposition. The deactivation of Ni/SiO₂was mainly due to the carbonousdeposition, while that of Ni₃P/SiO₂and Ni₂P/SiO₂resulted from the formation ofnickel phosphates that were inactive for the HDO of anisole. Among the nickelphosphide catalysts, Ni₃P/SiO₂presented high activity and stability.MgO, TiO₂, La₂O₃and CeO₂promoted the HDO performance of Ni₃P/SiO₂. Thelow Ce loading and the first addition of Ce species were favorable to improving theperformance of Ni₃P/SiO₂for demethylation, hydrogenation and deoxygenation, sincethey reduced the formation of difficultly reducible cerous phosphate.