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Catalytic activation and conversion of light alkanes by sulfated zirconia is unequivocally shown to be initiated by producing small concentrations of olefins. This occurs via stoichiometric oxidative dehydrogenation of butane by SO3 or pyrosulfate groups to butene (present mostly as alkoxy groups), water, and SO2. Thermal desorption and in situ IR spectroscopy have been used to determine all three reaction products. The concentration of butene formed determines both the catalytic activity of sulfated zirconia as well as the deactivation via formation of oligomers. The thermodynamics of the oxidative dehydrogenation of n-butane by different SZ surface structures has been examined by density functional (DFT) calculations. The calculations show that pyrosulfate or re-adsorbed SO3 species have the highest oxidizing ability.

LaCl 3 is an active, selective and stable catalyst for oxidative chlorination of methane to methyl chloride. Selective conversion to methyl chloride can be achieved by limiting methane conversion, for example, by using an excess of methane in the feed. Methylene chloride and carbon monoxide are the main side products at higher methane conversion levels. Transient OCl ) anion, formed by oxidation of Cl ) in LaOCl and LaCl 3 with molecular oxygen, is proposed to be the active site for the initial step of methane activation. CO x formation is proposed to proceed through the formation of adsorbed multiply substituted chloromethanes.

Butane activation has been studied using three types of sulfated zirconia materials, single crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia in interaction with SO(3) and water was established by DFT calculations, which was verified by LEED investigations on single-crystalline films and by IR spectroscopy on powders. At high sulfate surface densities a pyrosulfate species is the prevailing structure in the dehydrated state; if such species are absent, the materials are inactive. Theory and experiment show that the pyrosulfate can react with butane to give butene, H(2)O and SO(2), hence butane can be activated via oxidative dehydrogenation. This reaction occurred on all investigated materials; however, isomerization could only be proven for powders. Transient and equilibrium adsorption measurements in a wide pressure and temperature range (isobars measured via UPS on nanocrystalline films, microcalorimetry and temporal analysis of products measurements on powders) show weak and reversible interaction of butane with a majority of sites but reactive interaction with <5 micromol g(-1) sites. Consistently, the catalysts could be poisoned by adding sodium to the surface in a ratio S/Na = 35. Future research will have to clarify what distinguishes these few sites.

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The individual and combined effect of phosphoric acid modification, the addition of an alumina-based binder, and steaming on the acid-base and catalytic properties of HZSM-5 have been investigated. Whereas all three processes reduce the concentration of Brønsted acid sites, the underlying mechanisms and the extent of the effects vary. Upon addition of an alumina-based binder or during steaming of the parent zeolite dealumination is the sole process occurring. Impregnation of HZSM-5 with phosphoric acid leads to hydrolysis of framework aluminum and to the condensation of Brønsted acid sites with POH groups. This latter process can be reversed in the presence of an aqueous phase. In the forming process, this leads to the reversible formation of phosphate anions and phosphoric acid and the redistribution of phosphate species between the zeolite and the alumina binder. This mobility is mitigated by introducing phosphate species to the (alumina) binder indicating that in aqueous phase equilibrium between phosphate ions and phosphoric acid the zeolite and the (alumina) binder exists. Whatever the first step of modification of the parent material is (doping with H 3 PO 4 or addition of either alumina or phosphated alumina binder), steaming at elevated temperatures essentially reduces and equalizes the concentration of Brønsted acid sites. For all samples derived from one common parent zeolite, the rate of protolytic cracking of propane depends linearly on the concentration of strong Brønsted acid sites; that is, all modified materials have the same turnover frequency. This turnover frequency is notably higher than that of the parent material.

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