Certain relationships in predicting the activity of oxide catalysts

Abstract

1. In the model reactions of low-temperature hydrogenation of ethylene and double-bond migration in butenes, we have carried out a systematic investigation of the catalytic properties of the rare earths and the oxides of first-row and second-row transition elements and subgroups I and IIIb of the periodic table, as well as type Y zeolite in the Na, Cr, Nd, and La forms, and CeO2-Nd2O3 solid solutions. The data available in the literature on these reactions have been analyzed critically and refined, as well as data on the ortho-para conversion and homomolecular exchange of hydrogen and isotope deuterium exchange in hydrocarbons. 2. For the first time, we have established experimentally and justified theoretically the extremal dependence of specific catalytic activity of oxides on the calcination temperature. Activity of oxide systems is manifested only after partial dehydroxylation and desorption of acidic impurities (CO2, NO2, etc.). At the Tamman temperature, deactivation is observed. 3. In the reactions investigated, the low-temperature activity of oxides with a valence of the element equal to the number of the group increases from top to bottom and from right to left in the groups and periods of the periodic table. For oxides of a given element, the activity decreases with increasing degree of oxidation of the metal. It is suggested that the active centers are of a basic nature. 4. All oxide catalysts for low-temperature hydrogenation are also active, under similar conditions, in double-bond migration in olefins, homomolecular exchange and ortho-para conversion of hydrogen, and isotope deuterium exchange in hydrocarbons; the mechanism of catalyst action is similar in all of these reactions.