Comparison of n-Pentane Reforming Over Pt Supported on Amorphous and γ-Al2O3
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The n-pentane reforming activity of Pt supported on nonhydrolytic amorphous Al2O3 (Pt/NH–Al2O3), was investigated and compared to the catalytic activity of Pt supported on crystalline γ-Al2O3. The Pt was introduced by (a) impregnation with either a solution of H2PtCl6 in water or a solution of platinum acetylacetonate (PtAcac) in toluene; (b) in situ introduction of a Pt precursor, either PtBr4 or cis-bis(benzonitrile)platinum dichloride, before gelation of the NH alumina. The rate-controlling step in the reforming of n-pentane for both amorphous and crystalline aluminas was found to be the reaction on the alumina acidic sites. The Pt/γ-Al2O3 catalysts exhibit higher conversions of n-pentane and higher selectivity to isopentane, than the corresponding amorphous alumina samples. After 1.5 h at 400 °C, the highest conversion of the γ-Al2O3-based catalysts was ∼47% with 20.3% selectivity to isopentane. The highest conversion of the NH–Al2O3-based catalysts under the same conditions was only ∼26% with 13.6% selectivity to isopentane. The high intrinsic Cl content (2.6 wt%) of the amorphous alumina was found to have a minor effect on the activity of the alumina, compared to the activity of the more ordered γ-alumina. Catalysts prepared by impregnation of the NH alumina with aqueous chloroplatinic acid, exhibited higher conversions compared to catalysts prepared by impregnation of the NH alumina with a solution of PtAcac in toluene. This result occurred in spite of the lower surface area and lower Pt dispersions of the chloroplatinic acid-impregnated catalysts, and is explained by the formation of microcrystalline surface structures and existence of surface chlorine.
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