Influence of pH of the impregnation solution on the phosphorus promotion in W/Al2O3 hydrotreating catalysts

• Published in: Applied catalysis. A, General General, 2002-01, Vol.224 (1-2), p.97-110
• Main Authors: Cruz, J., Avalos-Borja, M., López Cordero, R., Bañares, M.A., Fierro, J.L.G., Palacios, J.M., López Agudo, A.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; Gas oil hydrodesulfurization; General and physical chemistry; Impregnation pH effect; Phosphorus promotion; Pyridine hydrodenitrogenation; Supported tungsten catalysts; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/S0926-860X(01)00774-8

W/Al2O3 and WP/Al2O3 catalysts, prepared by co-impregnation at different pH values (1.5, 7 and 9), were characterised by several techniques (XRD, TPR, Raman spectroscopy, SEM-EDX, XPS and HRTEM) and tested in the parallel hydrodesulfurization (HDS) of gas oil and hydrodenitrogenation (HDN) of pyridine. The results show that P addition, whichever the pH of the impregnation solution is, has a positive effect on HDS activity and, to a minor extent, on HDN activity. The promoter effect of P for gas oil HDS was clearly influenced by the impregnation pH, which increased substantially by decreasing the impregnation pH. This improvement in HDS activity is interpreted as a result of an increased homogeneous distribution of tungsten on alumina, formation of more polytungsten oxide species and incipient WO3 crystallites, and slightly greater sulfidation of the oxo-tungsten species, as well as a slight increase in WS2-like stacking. By contrast, the P promotion for pyridine HDN was not significantly affected by the impregnation pH, indicating that HDN activity is less sensitive to the changes in the W distribution than the HDS activity. The possible role of P in the catalytic properties of W/Al2O3 catalysts is discussed.