Alkane activation at low temperature on sulfated zirconia

硫酸化氧化锆是低碳烷烃异构化的一种非常活跃的催化剂。然而，催化剂表面发生的化学作用仍存在争议。该项目的目标是在硫化氧化锆表面形成烷烃活化步骤，并对财团(莱比锡大学)的海湾合作伙伴准备的样品进行测试。采用程序升温脱附(TPD)/反应、微量热法和原位红外光谱等原位表征技术，研究了正丁烷活化机理的初始步骤。在不同实验条件下正丁烷异构化和加氢异构化反应，包括~(13)C标记和重氢正丁烷的同位素标记研究，用微量热法计算出正丁烷异构化反应的表观活化能为43KJ/mol，表明该反应可以在室温下进行。随着混合物中异丁烯/正丁烷比的增加，正丁烷异构化反应的诱导期缩短，反应速率提高，从而得出异丁烷吸附形成的表面中间体参与了反应的结论。原位FTIR观察到的C8烃分子的形成和标记正丁烷反应过程中各种产物的分布表明，正丁烷异构化反应是以双分子机理进行的。正丁烷异构化反应可能涉及到氧化还原活性的氧化还原活性，这是由(I)与正丁烷TPD观察到的C8分子和(Ii)正丁烯的形成和水的脱附同时观察到的单硫酸盐的形成和双硫酸盐物种的消失所支持的。氧化还原化学途径在硫化氧化锆烃活化的初始步骤中的潜在作用引起了我们的注意。特别是，表面物种的转变和性质，即反应物物种和载体表面，必须用FTIR和拉曼光谱等原位技术来澄清。

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.