乙、丙烷选择氧化制含氧化合物和烯烃骨架限域的高分散隔离活性位催化剂研究

The direct conversion of light alkanes to chemical products with high added values is one of the hottest topics in the field of catalysis research. In this project, silica-based mesoporous molecular sieve catalysts containing framework-doped Mo or V active sites are to be developed and synthesized by the means of in-situ hydrothermal synthesis, and the optimal synthesis condition is to be investigated. The supply of active oxygen and conversion activity of alkane molecules can be controlled by the tuning of aggregation states and density of the framework-confined active sites in the catalysts. The isolated active sites can prevent the deep oxidization of desired products. It promotes the conversion of alkanes, improves the selectivity of the products and the stability of catalysts. It is to reveal the confinement principles for the framework-incorporated catalysts, to investigate the relationship between the surface nanostructure of catalysts and their catalytic performances. Especially, the development of the combined in-situ Raman-IR-MS characterization method is used to realize the accurate characterization of the active sites in the process of actual reaction conditions. By determining the structural changes of the catalysts, the rule for product distribution and catalytic reaction mechanism under the in-situ and dynamic conditions, a fundamental relationship between the physicochemical properties of framework-incorporated mesoporous molecular sieve catalysts and the essence of ethane/propane activation and the catalytic performance for the selective oxidation reaction are to be established on the atomic and molecular level. The realization of accurate design and building of restrained atom and electron structure offers scientific directions to design the active centers reasonably in the catalysts with the high catalytic performances for the selective oxidation of light alkanes.

低碳烷烃直接转化成高附加值的化工产品是当今催化领域的热点研究方向之一。本项目采用直接水热原位合成法研制高活性的钼、钒骨架掺杂的氧化硅基介孔分子筛催化剂，探索催化剂的最佳合成条件。通过调变骨架限域催化剂活性位的聚集状态和密度可调控活性氧的供给及烷烃转化活性，有效阻止目标产物发生深度氧化反应，提高产物的选择性和催化剂的稳定性。认识骨架掺杂催化剂的限域规律，探讨催化剂的表面结构与乙/丙烷选择氧化之间的构效关系，特别是发展原位Raman-IR-MS联用表征手段，实现催化活性位点在实际催化反应条件下对反应过程进行精准表征，在原位、动态条件下研究催化剂的结构变化及产物分布规律，探讨反应机理，从而在分子/原子水平上建立骨架限域介孔分子筛催化剂的物化属性与乙/丙烷活化及选择氧化催化性能之间的关系，实现活性位限域原子和电子结构的精准设计与构建，为低碳烷烃选择氧化高性能催化剂活性位进行理性设计提供科学依据。

天然气、页岩气中富含乙烷和丙烷，将其选择氧化为乙烯、丙烯和含氧化合物，具有重要的理论和现实意义。本项目对乙烷、丙烷选择氧化反应高分散隔离活性位催化剂的设计与制备规律进行了系统研究，研制出乙烷、丙烷选择氧化催化性能优异的骨架掺杂催化体系，并阐述了乙烷、丙烷选择氧化反应的机理。.以三维二氧化硅基介孔孔道的SBA-16、KIT-6、MCF为载体，采用直接水热法合成了几个系列骨架掺杂的Mo基高分散隔离活性位催化剂；采用水热合成与pH值调节结合的方法合成了骨架掺杂的V基高分散隔离活性位催化剂；采用微乳液法合成了SiO2纳米粒子骨架限域的V基催化剂。骨架掺杂不仅得到了高浓度的高分散隔离活性物种，且牢固地锚定了活性物种。.催化性能评价结果表明骨架掺杂的高分散隔离活性位催化剂具有较好的选择性和稳定性。其中：650 ℃时，0.5Mo-SBA-16催化剂上乙烯产率达31.1%。0.5V-m-silica催化剂用于丙烷选择氧化反应，575 ℃烯烃及总醛选择性达76%。625 ℃时， K0.25/0.1Mo-KIT-6催化剂用于丙烷选择氧化反应，丙烯醛+烯烃收率高达53.4%。表征结果表明：掺杂型催化剂优异的催化性能归因于高浓度的高分散隔离活性位、较强抗积碳能力以及较高的稳定性。.通过前驱液酸碱配对和蒸发自组装方法合成了Cr掺杂ZrO2催化剂，结果表明：7Cr-ZrO2催化剂上初始丙烷转化率为68%，丙烯选择性为40.5%。原位Raman与DFT计算结果表明：高分散隔离的Cr3+是活性物种，少量的CO2与大量的H2产生积碳。.利用理论计算研究了隔离Mo基催化剂上乙烷选择氧化反应机理：含有两个Mo=O的催化剂更容易催化乙烷选择氧化反应；乙烷选择氧化反应生成乙醛是经过乙醇中间体和表面Mo(OH)(OC2H5)中间体进行。.基于DFT第一性原理计算，通过调变载体来调变Pt的电子结构，优化单原子Pt催化剂上丙烷直接脱氢反应的催化性能。对于石墨烯负载的单原子Pt催化剂，结果表明：杂原子B、N掺杂可调控载体性质，改变催化剂的电子结构，进而调控催化性能；对于氮化硼负载的单原子Pt催化剂，结果表明：负载在硼空穴上的Pt比在氮空穴上的具有更好的活化碳氢键能力。