丙烷脱氢制丙烯用Pt基双金属纳米催化剂的设计与合成

The Pt-Sn bimetallic catalyst is environmentally friendly, and it has higher catalytic activity for propane catalytic dehydrogenation. However, the formations and effects of the component Sn in a bimetallic catalyst remains elusive and still under debate. Although Sn is one of the most efficient promoters, the deactivation due to coke formation on the catalysts is not completely eliminated, and the catalysts still have a short lifetime. The tolerance to coke deposition and the stability of Pt-Sn catalyst need to be improved. Therefore, understanding the nature of Sn and the process of coke deposition will be the key to improve the catalystic performance. In this project, a series of PtxSny nano alloy materials will be prepared from carbonyl compounds containing the Pt and Sn atoms, and they will be applied as a catalyst in the propane dehydrogenation. The effects of catalyst structural properties on the catalytic performance, such as the formations of Sn, the Pt-Sn alloy phases and the size of nanoparticles, will be investigated by catalysts characterizations and valuations. In addition, the coking behavior during propane dehydrogenation will be studied by thermogravimetry analysis. Furthermore, the efforts will be put into the investigation of the relationship among the catalyst structural properties, the catalytic performance and coking, which will gain insights into the role of Sn and the mechanistic aspects of catalyst deactivation. Based on the above researches, the catalyst optimization theory will be deducted and provide the theoretical guidance for the design of highly efficient catalysts with high activity, selectivity and stability in the propane dehydrogenation. The successful implementation of this project will also provide some theoretical guidance and basic data to develop the novel catalysts for the dehydrogenation of lower alkanes.

Pt-Sn催化剂应用于丙烷催化脱氢，具有环境友好、活性高等优点，但Sn的存在价态及其作用尚无定论，且催化剂的抗积炭和稳定性能仍有待提高。对Sn作用本质及其积炭机理的认识将是催化剂性能改善的关键。本课题将在前期工作的基础上，综合考虑催化剂设计以及反应条件，以Pt、Sn的羰基化合物为前体来合成一种高纯PtxSny纳米合金催化剂，并将该材料应用到丙烷脱氢反应中；综合材料表征及脱氢性能评价，得到催化剂的结构参数，如Sn的化学状态、晶相结构、粒径大小等与脱氢性能之间的关联机制；进一步采用热重分析结合材料结构表征，研究催化剂结构参数与积炭速率之间的关联机制。利用这种关联结果和结论，总结Sn的作用及催化剂失活机理，推导出催化剂优化理论并对催化剂设计进行指导，以期得到具有高活性、高烯烃选择性和高稳定性的丙烷脱氢催化剂。该课题的实施可为研发新一代低碳烷烃脱氢催化剂提供一定的理论指导和基础数据。

随着丙烯需求量的增长以及页岩气开采技术的日趋成熟，丙烷脱氢制丙烯工艺日益受到重视。针对丙烷脱氢Pt-Sn催化剂Sn存在形式以及Pt烧结、积炭失活的问题，本项目以Pt、Sn羰基金属化合物为前体，通过调节Pt:Sn原子比制备了负载型PtxSny纳米合金催化剂，利用BET、XRD、TEM、FTIR、TG-DTA和拉曼光谱等表征结合丙烷脱氢评价，研究了催化剂物理结构性质与脱氢性能之间的关系，并进行了积炭分析。结果表明，当Pt:Sn比为3:1时，催化剂上主要存在形式为Pt3Sn合金，分散性高，粒径较小，平均粒径为1.49nm；载体Al2O3要优于SiO2、ZSM-5，其负载催化剂制备条件为：CH3COONa·3H2O: Pt4+摩尔比为8:1，Pt负载量0.5wt%，H2氛围、200℃脱羰基；适宜反应条件为580 ℃、常压、丙烷质量空速（WHSV）4 h-1、丙烷/氢气进料比4/1，该条件下Pt3Sn/Al2O3的丙烯选择性和催化稳定性明显优于浸渍法Pt-Sn催化剂。Sn负载量较低时，铂、锡在催化剂上主要以Pt3Sn、PtSn合金形式存在，可有效抑制金属颗粒的高温烧结、改善催化剂脱氢性能。随着Sn负载量的增加，催化剂上L酸性位逐渐减少，丙烯选择性增加，同时可促进反应积炭从金属表面向载体迁移，提高催化剂稳定性。第二助剂添加研究表明，碱金属Na，碱土金属Ca、Mg可较好的中和载体的酸性位点，提高丙烯选择性；Ce的加入可增强金属与载体之间的相互作用，提高催化剂稳定性；Zn的添加可使催化剂上金属颗粒粒径减小、分散更加均匀，同时降低载体表面酸量，改善脱氢性能。积炭研究表明，催化剂上积炭主要表现为烯烃性质和芳香烃性质；随着Sn添加量的增加、原料中H2含量增加、丙烷WHSV降低以及金属粒径的减小，积炭的石墨化程度不断增加；随着温度和丙烷WHSV的增加，积炭量及初始积炭速率均呈幂律函数形式增加。再生实验表明，再生温度为520℃，空气WHSV为4h-1，再生时间为2h。本项目研究结果可为丙烷脱氢高效PtxSny合金催化剂的开发在理论与实践研究上提供一定的基础数据。