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Abstract

The reactivity of sulfated zirconias using small alkanes as probes is described. Sulfated zirconia promoted with iron and manganese was tested for the conversion of propane at 473-723 K, and for the conversion of neopentane (2,2-dimenthylpropane) at 623-723 K in a flow reactor at atmospheric pressure, and at reactant partial pressures {<=}0.05 bar. The major products of propane conversion at 473 K are butanes, accompanied by methane and pentanes. Formation of these products can be explained with oligocondensation and cracking reactions analogous to the reactions of alkanes observed by G. Olah in liquid superacids. At 723 K, propane conversion gives methane, ethane, ethene, and propene; neopentane conversion gives predominantly methane. The products and product ratios can be explained with a monomolecular cracking mechanism first described by Haag and Dessau. Deactivation of the iron- and manganese-promoted sulfated zirconia occurs in the first few hours on stream. Manganese, iron, cobalt, nickel, and zinc were investigated as single promoters of sulfated zirconia. The promoted samples were tested for n-butane conversion at 373 K and 0.005 bar n-butane partial pressure. The activity for n-butane conversion in this row of promoters decreased from left to right in the periodic table, high activity was linked to rapid deactivation. In order to elucidate the number and nature of sites on sulfated zirconia and its derivatives, a thin film model system is developed, which will facilitate the collection of interpretable data in acidity characterization experiments. (orig.)