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Title: Estudo de catalisadores Pt-In/Nb2O5 na conversão de hidrocarbonetos
Other Titles: Study of catalytics Pt-In/Nb2O5 in the hydrocarbons conversion
Keywords: Catálise heterogênea;  Heterogeneous catalyst;  Catalisadores;  Catálise;  Hidrocarbonetos - conversão;  Hydrocarbons - conversion
Issue Date: 15-Sep-2003
Publisher: Universidade Federal Fluminense
Abstract: Hydrocarbon dehydrogenation is an important industrial process, due to the high demand of unsatured hydrocarbons for industrial processes and products. Unsatured hydrocarbons are used in the manufacture of several products, such as detergents, high octanage gasoline, pharmaceutical products and synthetic rubber. The commercial catalysts employed in the hydrocarbon dehydrogenation process is based on platinum supported on alumina. The intrinsic acidity of the support is neutralized by an alkaline or alkali earth metal, usually lithium. Indium and tin are used as promoters of the metallic phase. The present work aimed to study the property of niobia supported Pt catalysts modified by In. Nióbia is a reductible oxide, able to promote a strong metal support interaction effect (SMSI). Pt/Nb2O5 catalysts were investigated recently in the dehydrogenation of alkanes and they presented promissing results. Pt/Nb2O5 and Pt-In/Nb2O5 were prepared by incipient wetness and characterized by temperature-programmed reduction (TPR), UV-Vis diffuse reflectance spectroscopy (DRS), H2 and CO chemisorption, H2 and CO temperature-programmed desorption (TPD), besides temperature-programmed oxidation (TPO). The catalytic activity of these catalysts was evaluated in the cyclohexane dehydrogenation, methylcyclopentane hydrogenolysis, n-heptane conversion and methylcyclopentane reforming. The analysis of TPR profiles allowed to conclude that there is an interaction between Pt and In in the bimetallic catalysis, which was confirmed by the decrease in the adsorption capacity measured by the H2 and CO uptakes. In addition it also inhibited the metal support effect (SMSI) between platinum and niobia. Cyclohexane dehydrogenation results demonstrated the creation of new interfacial sites for Pt/Nb2O5 catalysts. Hydrogenolysis reactions were suppressed by the presence of the SMSI effect and by the presence of In, as observed in the methylcyclopentane hydrogenolysis. In the n-heptane conversion, all the niobia-supported catalysts displayed a high selectivity for the olefin formation. The presence of In decreased the formation of hydrogenolysis products and increased the stability of the catalyst. In the reforming methylcyclopentane all the catalysts displayed a high selectivity for the dehydrogenation products.
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