Preparation, characterization, hydrodesulfurization and hydrodenitrogenation activities of alumina-supported tungsten phosphide catalysts

Two series of WP/Al2O3 catalyst precursors with WP mass loading in the range 18.5%-37.1% were prepared using the impregnation method and mixing method, respectively, and the catalysts were then obtained by temperature-programmed reduction of supported tungsten phosphate (precursor of WP/Al2O3 catalysts) in H-2 at 650 degrees C for 4h. The catalysts were characterized by XRD, BET, TG/DTA, XPS and P-31 MAS-NMR. The activities of these catalysts were tested in the hydrodenitrogenation (HDN) of pyridine and hydrodesulfurization (HDS) of thiophene at 340 degrees C and 3.0MPa. The results showed that owing to the stronger interaction of the support with the active species, the precursor of WP/Al2O3 catalyst was more difficulty phosphided and a greater amount of W species was in a high valence state W6+ on the surface of the catalyst prepared by the impregnation method than that by the mixing method. P-31 MAS-NMR results indicated that P-31 shift from 85% H3PO4 of 2.55 x 10(-4) for WP and 2.57 x 10(-4) for WP/gamma-Al2O3 catalysts prepared by mixing method. Such WP/Al2O3 catalysts showed higher HDN activities and lower HDS activities than those prepared by the impregnation method under the same loading of WP. WP/gamma-Al2O3 catalysts with weak interaction between support and active species were favorable for HDN reaction while the WP/gamma-Al2O3 catalysts with strong interaction were favorable for HDS reaction.