Alkane activation at low temperature on sulfated zirconia

硫酸氧化锆是一种非常活跃的轻烷烃异构化催化剂。然而，在催化剂表面发生的化学反应仍然存在争议。该项目旨在获得硫酸氧化锆表面烷烃活化步骤的形成，并对财团合作伙伴（莱比锡大学）制备的样品进行了测试。采用程序升温解吸(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的初始步骤。不同实验条件下的正丁烷异构化和加氢异构化，包括双13C标记和氘化正丁烷的同位素标记研究。用微量热法计算硫酸氧化锆上正丁烷异构化反应的表观活化能为43 KJ/mol，表明该反应可以在室温下进行。通过提高混合物中异丁烯/正丁烷的比例，观察到正丁烷异构化的诱导期缩短，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。原位傅里叶红外（FTIR）观察到C8烃分子的形成和标记正丁烷反应中产物的杂化分布表明，正丁烷异构化是通过双分子机制在硫化氧化锆上发生的。正丁烷异构化步骤可能涉及硫酸氧化锆载体的氧化还原活性，其支持条件是：(1)单硫组分的形成和双硫组分的消失同时观察到C8分子的形成；(2)正丁烷TPD观察到正丁烯和水的脱附。氧化还原化学途径在硫酸盐氧化锆上烃类活化初始阶段的潜在作用引起了我们的关注。特别是，表面物质（即反应物和载体表面）的转化和性质必须使用FTIR和RAMAN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.