FT-IR AND SOLID-STATE NMR INVESTIGATION OF PHOSPHORUS PROMOTED HYDROTREATING CATALYST PRECURSORS

The effect of phosphorus on the structure of NiMo/Al2O3 hydrotreating catalyst precursors has been investigated. Calcined and reduced P/Al2O3, PNi/Al2O3, P-Mo/Al2O3, and PNiMo/Al2O3 (where the wt% P = 0.0 to 10.0, wt% Mo = 8.0 to 12.0, and wt% Ni = 4.0) have been studied using FT-IR, XRD, and 31P and 27Al MAS NMR techniques. Phosphoric acid reacts with alumina hydroxyls forming monomeric and polymeric phosphates. At the higher phosphorus loadings, aluminum phosphate is also formed. On calcined PNi/Al2O3, nickel phosphate is formed. This leads to a decrease in density of NO sites in the reduced state as measured by CO adsorption. The addition of up to 1.5 wt% P to Mo(8)/Al2O3 promotes the formation of octahedral molybdena on the alumina surface. However, the addition of > 2.0 wt% P results in the formation of bulk M003 and Al2(MoO4)3 in both PMo(8)/Al2O3 and PMo(12)/Al2O3. CO adsorption on reduced PNi(4)Mo(8)/Al2O3 samples shows that the presence of 0.5 wt% P causes a significant increase in the number of sites adsorbing CO. Increasing the P loading further causes a decrease in the number of adsorbing sites; this decrease can be attributed to the formation of either nickel phosphate or nickel molybdate. © 1991.