Influence of Method of Introduction of Cu- and Zn-Based Modifiers on the Properties of Chromia–Alumina Catalysts

Abstract

Three methods of introduction of modifiers based on Cu and Zn compounds into the CrOx/Al2O3 catalysts for dehydrogenation of light paraffin hydrocarbons are considered: Introduction from sol, introduction using successive impregnation technique and introduction of modifiers by impregnation along with precursor of chromium oxide. The obtained samples are studied by a complex of physical-chemical methods (XRD, UV-Vis spectroscopy, temperature-programmed reduction with hydrogen (TPR-H2), X-ray fluorescent (XRF) spectrometry, low-temperature N2 sorption). The catalytic properties of the samples are studied in kinetic mode in isobutane dehydrogenation. Cu- and Zn-modifiers are shown to influence on the peculiarities of reduction of Cr6+ and, hence, specify the state of active surface of CrOx/Al2O3 catalysts formed in the reductive reaction medium. Not only do the states of modifiers influence on the initial activity of the catalyst, but also on its activity after oxidative regeneration. Introduction of modifiers by successive impregnation method results in formation of copper and zinc aluminates or defective spinels on the Al2O3 surface. When the active component is introduced, the modified surface of the support promotes formation and stabilization of Cr6+ sites that can undergo reversible reduction–oxidation and provide high activity and selectivity towards formation of isobutylene (>98%).