Catalytic behaviour of bifunctional pumice-supported and zeolite/pumice hybrid catalysts for n-pentane hydroisomerization

A series of phillipsite(zeolite)-rich pumice-based supports with different acidity, Si/Al ratios and textural properties were prepared by acid leaching using hydrochloric acid. The NH3-TPD profiles, chemical composition and nitrogen adsorption-desorption isotherms pointed out that textural and acidity properties depend largely on the acidification treatment conditions. Bifunctional catalysts based on platinum supported over protonated pumice have been prepared by ethanol impregnation and tested in n-pentane hydroisomerization. Very low conversions and yields to isopentane have been obtained. The small size of phillipsite channels, lower than the pentane molecule and the intermediate products, may be hindering the access of these molecules to the acidic sites, contributing to their low activity in the target reaction. However, the catalysts constituted by a physical mixture of pumice-supported platinum, with protonated commercial zeolites (H-Mordenite or H-ZSM-5), widely used for light paraffin isomerization, resulted in higher isopentane yields than the bifunctional commercial zeolite-based catalysts. These results are explained by the greater accessibility of metal sites in a wider pore support and by the lesser blocking of the acid surface placed in the zeolite micropores. (C) 2008 Elsevier B.V. All rights reserved.