Effect of Metal Dispersity on the Activity of Zeolite Catalysts Containing Transition Metals

Abstract

Publisher Summary This chapter discusses how the dispersity of metal particles on the catalytic activity affects the reaction of toluene disproportionation on nickel–zeolite catalysts. The latter are obtained by ion exchange (NiCaY and their mixed forms—CrNiCaY and PbNiCaY) by deposition (NiO/CaY) or by mechanical mixing of the constituents (NiO+CaY). The changes in the dispersity of the metal particles in the zeolite intracristalline structure are followed by the change in the size of the unit cell (X-ray data). The parameter of the unit cell and the average size of the nickel particles are determined in air-dry state, reduced state, state of maximal catalytic activity, and after deactivation. The X-ray date for the parameter of the unit cell of samples in different states provides information with respect to the changes taking place during Ni(II) reduction, the mutual effects between the cations in the zeolite framework and the possible changes during the interaction of the active sites with the substrate. The study of the catalytic activity of nickel—containing samples—reveals that when Ni(II) is reduced to metallic state only on the zeolite surface, only dealkylation takes place and the catalyst is soon deactivated. When Ni(II) ions are present in the zeolite structure (NiCaY), the major part of them is reduced to metallic nickel, which partially migrates and agglomerates on the zeolite surface as nickel crystallites, sized about 300–500 Ǻ and partially remains in the intracrystalline structure.