应用原位电子显微学技术研究碳化钼加氢催化剂的碳化过程与催化活性

Since discovery of the “platinum-like behavior” of metal carbide in 1973, thereafter transition metal carbides (TMCs) have been substantially studied as promising candidates alternative to precious metal catalysts in hydrogenation reactions. Despite of enormous effects on development of the new generation of cheap and low-toxic catalysts in sustainable energy and synthetic chemistry, many important research questions related with carburization process and catalytic mechanism remain unanswered, which was attributed to technology limitations and lack of proper characterization methods. In this project, in-situ transmission electronic microscopic techniques (TEM) will be employed to study carburization process of molybdenum oxides and subsequent catalytic hydrogenation of arenes under gaseous chemical environments. By using advanced diffraction techniques and spectroscopic tools, insightful understandings about evolution of microstructure and surface physicochemical properties during the dynamic processes at nanoscales and sub-nanoscales could be obtained. Meanwhile, supported by theoretical calculations done by Institute of Coal Chemistry, Chinese Academy of Sciences and Synfules China, a convincing model about active phase of Mo2C for catalytic hydrogenation will be established based on the in-situ microscopic data. We believe that the successful characterization of the important catalytic process at the nanoscale will be of vital importance for both academia and industry, which could direct design and synthesis of high-efficient hydrogenation catalysts.

金属碳化物，特别是碳化钼，具有类铂催化加氢性能，被工业界视为未来替代贵金属催化剂制备高效，廉价，低毒环保加氢催化剂的重要候选材料之一。但是由于表征技术的有限，我们对碳化钼的合成和催化活性的认识被分散的广域和离线测试结果所限制，使我们无法深入理解碳化机理和以及所导致的催化活性相/位的生成。本项目拟采用原位透射电子显微技术为表征手段，研究真实气态化学环境下纳米到原子尺度氧化钼前驱体的碳化及催化芳香烃加氢反应。通过先进的衍射工具和谱学方法获取反应过程中局域的晶体结构和物理化学性质，为更深入地理解催化剂表面活性相的形成和催化过程提供更直观和有说服力的结果。研究并结合山西煤化所及中科合成油公司量化计算的成果，建构可能的纳米催化活性相模型和表面化学环境解析，为高性能加氢催化剂的定向设计与改性提供直观依据和理论指导。

碳化钼作为一种具有类贵金属催化活性的新型催化剂，对于发展新型环保催化剂和新能源化工都具有重要的意义，但研究者对碳化钼可控合成和合理设计的认识依旧有限，对于碳化钼催化剂碳化机理及负载催化剂的活化过程缺乏深入的，清晰的理解，这严重阻碍深入研究其构效关系，优化和发展新型高效碳化钼催化剂。在这个工作中，执行人以原位透射电镜为主要表征工具，结合其他表征手段和理论计算，对与碳化钼相关的催化剂和催化反应进行了深入的研究。通过原位电镜，执行人发现在真实碳化环境下，氧化钼前驱体经历了混合拓扑转化(topotactic)和假晶相变(pseudomorphic)两种转化过程的碳化，厘清了长期以来对于氧化钼碳化机理的争议，为设计新型碳化钼催化剂提供了微观结构相关的证据。同时利用原位电镜为主的表征手段，观测到纳米至原子尺度真实化学环境下纳米金属颗粒在碳化钼载体上的动态弥散过程，证实了金属颗粒与碳化钼载体之间的强相互作用，为设计新型负载碳化钼催化剂提供了科学的证据。执行人结合理论计算，揭示了碳化钼与负载金属颗粒间存在强相互作用的根本原因，并合理解释了负载金属碳化钼催化剂对于芳香化合物具有较好催化加氢能力的原因。这些成果极大的丰富了我们对于碳化钼催化剂的认识，也有助于我们创制新型碳化钼催化剂和设计新型催化反应。