Bifunctional nature of a SiO2-supported Ni2P catalyst for hydrotreating : EXAFS and FTIR studies

• Published in: Journal of catalysis 2006-04, Vol.239 (2), p.376-389
• Main Authors: LEE, Yong-Kul, OYAMA, S. Ted
• Format: Article
• Language: English
• Subjects: CARBON MONOXIDE; CATALYSIS; CATALYST SUPPORTS; CATALYTIC EFFECTS; CHEMICAL PREPARATION; CHEMISORPTION; Chemistry; DENITRIFICATION; DESULFURIZATION; DISULFIDES; Exact sciences and technology; General and physical chemistry; HYDROGENATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MORPHOLOGY; national synchrotron light source; NICKEL PHOSPHIDES; POLYCYCLIC SULFUR HETEROCYCLES; PYRIDINE; QUINOLINES; SILICON OXIDES; SURFACE PROPERTIES; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2005.12.029

A Ni2 P catalyst supported on a high-surface area SiO2 (350 m2 g-1 ) was prepared by temperature-programmed reduction, and its structural and surface properties were studied. X-ray diffraction and extended X-ray absorption fine structure measurements were used to obtain structural parameters for the supported Ni2 P phase, and Fourier transform infrared (FTIR) analysis with the probe molecules CO and pyridine was carried out to characterize the surface properties. The catalytic activity was measured at 573 K and 3.1 MPa in a three-phase fixed-bed reactor for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) using a model liquid feed. At standard conditions using 500 ppm S as 4,6-dimethyldibenzothiophene (4,6-DMDBT), 3000 ppm S as dimethyldisulfide, 200 ppm N as quinoline, and 1% tetralin in a tridecane solvent, the Ni 2 P/SiO2 gave an HDS conversion of 85%, an HDN conversion of 100%, and a tetralin conversion of 37%, which were much higher than those of a commercial Ni-Mo-S/Al2 O3 catalyst, which gave an HDS conversion of 41%, an HDN conversion of 98%, and a tetralin conversion of 20% based on equal numbers of sites (240 μmol) loaded in the reactor. The sites were counted by CO chemisorption for the phosphide and by low-temperature O 2 chemisorption for the sulfide. The Ni2 P/SiO2 catalyst favored the hydrogenation (HYD) pathway for 4,6-DMDBT HDS to generate methylcyclohexyltoluene and dimethylbicyclohexane with a relative HYD selectivity of 95%. It also favored hydrogenation for tetralin to give decalin with a relative HYD selectivity of 89%. The Ni 2 P/SiO2 catalyst also showed better resistance to N-compounds than the Ni-Mo-S/Al2 O3 catalyst. The FTIR spectra of adsorbed CO showed that the Ni site in the Ni2 P phase gave rise to considerable π-back bonding, which was related to the high activity of the Ni2 P/SiO2 catalyst in the hydrogenation of aromatics. The FTIR spectra of adsorbed pyridine showed that the Ni2 P phase had a P[single bond]OH group associated with Brønsted acidity that was active for the protonation of N compounds. These results thus suggest that the supported Ni2 P catalyst has bifunctional properties that are beneficial for catalytic activity in hydroprocessing.