Keynote address. Transition metal phosphides: New catalysts for hydroprocessing.

Abstract

The petroleum refining industry is currently faced with a dual challenge: stringent regulations that require a redn. of sulfur levels in transportation fuels, and a decline in the quality and availability of feedstocks. It has been recognized that current hydrotreating catalysts are not able to meet these requirements, and this has given rise to a widespread research effort to try to develop a new generation of catalysts. This talk will describe a novel class of hydroprocessing catalysts that differ fundamentally from existing sulfide-based catalysts. The new materials are the phosphides of transition metals, a class of robust metallic substances that include VP, NbP, MoP, WP, ReP, FeP, CoP, and Ni2P. These materials have ideal properties for catalysis; they are phys. strong and chem. stable, and inexpensive to prep. and regenerate. Tests in a trickle bed reactor at realistic conditions show that certain compns. are substantially more active than a com. sulfided Ni-Mo-S/Al2O3 in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene and the hydrodenitrogenation (HDN) of quinoline. Moreover, the phosphides are tolerant of sulfur and stable for over 100 h. In order to gain insight on the mechanism of HDN, the most difficult of the hydroprocessing reactions, the role of acid/base reactions is assessed by in situ reaction probes. These consist of a series of pentylamines and piperidines with different structures (different nos. of and hydrogens) that are expected to react differently depending on properties of the surface. This allows detn. of whether HDN occurs by elimination or displacement. The results are related to the acid and base sites obsd. on the surface by the IR spectroscopy of probe mols. and quantitated by adsorption and temp.-programmed reaction techniques. [on SciFinder(R)]