Alkane activation at low temperature on sulfated zirconia

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Sulfated zirconia is a very active catalyst for light alkane isomerization. However, the chemistry occurring at the catalyst surface is still under controversy. The projekt aims to obtain formation on alkane activation steps at the surface of sulfated zirconia and samples prepared bay partners in the consortium (Leipzig University) are tested. In situ characterization techniques including temperature programmed desorption (TPD)/reaction, microcalorimetry and in situ IR spectroscopy, are used to study the initial steps of n-butane activation mechanism. N-butane isomerization and hydroisomerization under various experimental conditions including isitope labeling studies with doubly 13C labeled and deuterated n-butane.The apparent activation energy of n-butane isomerization on sulfated zirconia calculated using microcalorimetry is 43 KJ/mol, which led us to conclude that the reaction can occur at room temperature. A decrease of the inducing period and an icrease of the reaction rates for n-butane isomerization are observed by increasing the isobutene/n-butane ratio in the mixture leading to the conclusion that surface intermediates formed by adsoption of iso-butane are involved in the reaction. The formation of C8 hydrocarbon molecules observed by in situ FTIR and the miscellaneous distribution of products observed during reactions using labeled n-butane imply that n-butane isomerization occurs on sulfated zirconia via a bimolecular mechanism. The n-butane isomerization step is suspected to involve a redox activity of the sulfated zirconia support, which is supported by (i), the formation of mono-sulfuric species an the disappearance of bi-sulfuric species observed simultaneously to the formation of C8 molecules an (ii) n-butene and water desorption observed by n-butane TPD. The potential role of a redox chemistry route in the initial step of hydrocarbon activation on sulfated zirconia focuses our attention. In particularly, the transformations and the nature Auf the surface species, i.e., reactant species as well as support surface, has to be clarified using in situ techniques such as FTIR and RAMAN spectroscopy.