Active phase of a nickel phosphide (Ni2P) catalyst supported on KUSY zeolite for the hydrodesulfurization of 4,6-DMDBT

Ni2P catalysts supported on potassium ion-exchanged ultrastable Y zeolites (KUSY) were prepared by temperature-programmed reduction (TPR), and the effect of Ni2P loading and initial Ni/P ratios on the hydroprocessing performance was studied. X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) were used to obtain structural parameters. Transmission electron microscopy (TEM) analysis showed that the KUSY-supported Ni2P samples consisted of nanoparticles, which were likely situated in the mesoporous cavities or the external surfaces of the zeolite crystals. The catalytic activity was measured at 613 K and 3.1 MPa in a three-phase fixed bed reactor for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) using a model liquid feed containing 500 ppm S as 4,6-dimethyldibenzothiophene (4,6-DMDBT), 500 ppm N as quinoline, and 3000-6000 ppm S as dimethyldisulfide (DMDS). Partial exchange with K enhanced the catalytic activity for the HDS of 4,6-DMDBT and resistance to N-compound inhibition. The Ni2P/KUSY had high activity with an HDS conversion of 99%, and an HDN conversion of 100%, which were much higher than those of a commercial Ni-Mo-S/Al2O3 catalyst with an HDS conversion of 80% and HDN conversion of 100%, based on equal sites (240 mu mol) loaded in the reactor. The sites were counted by CO chemisorption for the phosphide and by low-temperature O-2 chemisorption for the sulfide. Deficiency of P in the Ni2P resulted in deactivation, probably due to susceptibility to sulfidation. EXAFS analysis of the catalysts showed that the addition of extra P led to an increase in Ni-P coordination with lengthening of Ni-Ni bond distances, resulting in a high and stable catalytic activity. (C) 2007 Elsevier B.V. All rights reserved.