Influência do pré-tratamento em O2 e H2 sobre a atividade do Cr2 O3/MnO na desidrogenação do isopropanol.

Abstract

The variation of isopropanol dehydrogenation activity of redox Cr203/Mn02 catalyst pretreated with 02 and H2 has been studied using a "U" type, isothermic, continuous tubular reactor at atmosferic pressure. The following samples having their mass percent composition of Cr203 as 0; 2.5; 5.0; 10.0; 20.0 and 100 were prepared by the method of solution evaporation of Chromium (III) nitrate with manganese oxide. These precursores were calcined for 5 hours at 400, 450 and 700 °C. The activities were measured in terms of percent conversion of isopropanol by hydrogen gas evolution. The following results have been observed: (a) the 5% Cr203/Mn02 catalyst showed highest activity (conversion) among the prepared catalysts and was selected to study the effect of other factors; (b) the 5% Cr203, Mn02 catalyst showed higher and stable activity when pretreated by H2 for a period of 10 hours of continuous use; (c) the effect of external diffusion of the reagent over 5% Cr203,'Mn02 catalyst was neglegible upto a residence time of l.Ogcat.h.mol-1; (d) the catalytic activity of 5% Cr203/Mn02 catalyst decreased with the increase of time of reduction and reached a constant value at reaction temperatures 300, 330 and 360 °C; (e) with increase in reaction temperature from 300 to 360 °C, the activity of the catalysts 5% Cr203/Mn02, Cr203 and Mn02 got increased; (f) the average apparent energy of activation of 5% Cr203/Mn02 catalyst pretreated with 02 and H2 is found to be 20.70 Kcal/mol; (g) the activity of 5% Cr203/Mn02 catalyst decreased with the increase in calcination temperature of the catalysts in the range of 400 to 700 °C.