Selectivity and activity factors in bismuth-molybdate oxidation catalysts

Abstract

Selective catalytic oxidation and ammoxidation of olefins to the corresponding diolefins, unsaturated aldehydes, acids and nitriles accounts for about one-fourth of the industrial chemicals produced by allylic oxidation processes. Selectivity and activity in these processes is achieved by means of catalysts in which key catalytic functions are optimized in a single phase of a multi-phase mixed metal oxide. Such catalysts contain active sites capable of olefin chemisorption, ammonia activation, alpha hydrogen abstraction to generate an allylic intermediate, oxygen and NH insertion into the allylic intermediate, lattice oxygen migration from the bulk to the surface active sites, and dioxygen reduction and incorporation of oxide ions into anion vacancies of the catalyst structure. Bismuth molybdates are one such class of materials which contain all of the key catalytic features to affect selective olefin oxidation and ammoxidation of olefins. The design of effective catalysts is based on a molecular level understanding of surface atomic composition, phase composition of the bulk, oxidation states of the materials and defect structure of the solid phases.