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Activity and mechanism of the catalytic action of rare-earth oxides in low-temperature ethylene hydrogenation

Journal Article · · J. Catal.; (United States)
The variation in catalytic activity of rare-earth oxides and their analogs, scandia and yttria, in ethylene hydrogenation between -120 and 20/sup 0/C has been studied as a function of the temperature of pretreatment. Thermal analysis has been used to study the decomposition of the hydroxides from which the oxides were prepared. The oxides show catalytic activity after pretreatment at 600/sup 0/C when dehydration, decarboxylation, and denitroxylation have gone to completion and, in addition, when partial dehydroxylation of the surface has also taken place. Sesquioxides showed high activity, whereas dioxides were of low activity. A decrease in hydrogenating activity in the series of oxides from lanthana to lutecia correlates with a decrease in their basicity. As was shown by means of thermodesorption, hydrogen and ethylene are chemisorbed in two forms. With dysprosia it has been shown, by using deuterated species, that ethylene hydrogenation proceeds by involving loosely bound forms of hydrogen and ethylene via a semihydrogenated complex. Associatively adsorbed ethylene is involved in the reaction, and hydrogen activation is likely to be the limiting step.
Research Organization:
Zelinsky Inst. of Organic Chemistry, Moscow
OSTI ID:
5457025
Journal Information:
J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 49:2; ISSN JCTLA
Country of Publication:
United States
Language:
English