高性能纳米限域的丙烷脱氢制丙烯催化剂研究

Pt-based catalyst with the high performance is the key to the industrialization of propane dehydrogenation to propylene. In this project, several technologies include gas-bubbling-assisted membrane reduction (GBMR) method were used to prepare mesoporous oxide supported core-shell Pt/Sn or Pt/oxide nanometer catalysts. The interface effect between core and shell, and the protection of oxides on Pt particles can be effectively utilized to improve the catalytic activity and thermal stability of catalysts. The catalytic performance and stability condition of electrons and charge groups on catalyst interface can be illustrated. In-situ synthesis way was implemented to dope the metal into the framework of mesoporous molecular sieve. Compared to the supported catalyst, metal-doped catalyst can give more active sites with nanometric confined effect for the catalytic dehydrogenation of propane. In addition to improve the propane conversion, it can also prevent the deep reaction of propylene and realize the controllability of product structure, and improve the efficiency of the propane dehydrogenation reaction. In-situ Raman-IR-MS spectra were used to obtain the direct evidence of the change of surface active species. The activation of C-H bonds and the change of C-C bonds can be clarified, which is related to the highly efficient conversion of propane molecules. The relationship between the conversion and selectivity of propane and the behavior of electrons of catalyst surface can be understood. It will provide scientific basis to design and prepare the highly active Pt-based catalysts with the mesoporous supported/framework-incoporated materials at the atomic and molecular level.

高性能Pt基催化剂是丙烷脱氢制丙烯工业化的关键。本项目采用气膜辅助扩散还原等技术制备介孔氧化物担载核壳结构的纳米复合Pt/Sn或Pt/氧化物催化剂，利用核壳之间的界面效应及氧化物对Pt的保护作用，明确电子、电荷群体在催化剂界面的限域行为及稳定性条件，提高催化剂的活性和高温热稳定性。采用原位合成方式，将金属掺杂到介孔分子筛的骨架中。与担载型催化剂相比，骨架掺杂可获得纳米限域的高浓度活性位的丙烷脱氢催化剂，在提高丙烷转化率的同时，阻止丙烯深度反应，实现产物结构的可控性，提高了丙烷脱氢反应的效率。利用原位Raman-IR-MS联用仪等获取表面活性物种变化的直接证据，明确丙烷分子高效转化相关的C-H键活化及C-C键变化，理解丙烷转化率、选择性与催化剂表面电子行为的关系，为从原子、分子水平设计和制备高性能的介孔材料担载/骨架掺杂Pt基纳米催化剂提供科学依据。

丙烯是最重要的有机化工原料，随着我国经济的不断快速增长，未来对于丙烯的需求将逐渐增加。目前传统制取丙烯的方法已经无法满足人们的需求。丙烷在我国的储量十分丰富，由丙烷制取丙烯已经成为了增产丙烯的重要手段，有着极大的经济价值和社会意义。本项目设计并制备了一系列不同的负载型铂基催化剂进行表征和性能研究，取得主要成果如下：.（1）设计并制备了一系列以介孔微球和各种介孔分子筛为载体的负载型铂基催化剂，微球做载体的催化剂表现出了最好的活性，初始转化率均达到了50%以上并保持良好的稳定性。添加CTAB后的催化剂的结构与活性均发生了变化，说明通过添加CTAB进而改变催化剂的性能的方法可行，为以后丙烷脱氢催化剂的研究提供了思路。钛改性催化剂拥有较长寿命，有着较好的应用前景。.（2）通过对一系列骨架掺杂金属介孔分子筛的制备和表征，发现了骨架掺杂金属催化剂的分子结构与物理化学性质之间的关系。在适量的钛添加条件下，钛改性负载型催化剂展现出了优良的催化活性，转化率和稳定性均得到显著提高，样品上积碳生成速率较低，积碳物种的尺寸相对较小，增加丙烯选择性和催化剂寿命。.（3）研究了PtSn催化剂中不同金属载量对其积碳的影响，通过表征发现不同金属负载量的催化剂上其产生的积碳在本质上是基本相同的。所制备活性最佳催化剂在铂锡含量相对较低时获得，制备催化剂的成本相对其他贵金属催化剂的成本低，此时的转化率较高，并且选择性也很高，有较高的应用价值。.（4）成功获得了高活性抗积碳稳定性的丙烷脱氢制丙烯催化剂。通过原位拉曼表征可知，钛改性的催化剂样品上积碳生成速率较低，积碳物种的颗粒尺寸相对较小。同时钛组分可以提高催化剂的选择性和稳定性。