基于化学链过程选择性氧化脱氢丙烷制丙烯的氧载体设计及机理研究

Propylene serves as a core raw-material in the modern chemical industries and it has seen a significant increase in demand in recent years. Propylene is mainly derived from traditional process of naphtha steam-cracking, the non-oil route of the catalytic dehydrogenation of propane is attracting more attention. By employing the chemical looping oxidation-reduction process, this project chooses the low-cost multiple transition metal oxides as the oxygen carriers with specific lattice oxygen structure to achieve the selectively oxidative dehydrogenation of propane to propylene. The chemical-looping process is not limited by the thermodynamic equilibrium and deactivation of catalyst caused by carbon deposition in the anaerobic dehydrogenation of propane. The process also overcomes the problem of the deep oxidation in oxidative dehydrogenation reaction. The crucial challenges for developing efficient oxidative dehydrogenation of propane in the present project includes: (1) the structure control of the lattice oxygen; (2) the understanding of the mechanisms for oxygen migration and C-H activation processes; (3) the enhancement in both the oxidation-reduction property and the cycling stability. Combining precise control of the structure of metal oxides, coupled or in-situ spectroscopic characterizations and atom-scale theoretical calculations, a reliable relationship of structure and activity for oxygen carrier can be established. Based on the understanding for material synthesis, structure-activity correlation and intrinsic mechanism in the chemical looping process, the project aims at exploring novel metal oxide oxygen carriers with superior performance for the target reaction.

丙烯作为现代化学工业的重要基础原料，其需求量近年来显著增加。目前丙烯主要来源于传统的石脑油蒸汽裂解过程，但是以丙烷为原料催化脱氢制丙烯的非石油路线正受到越来越多的关注。本项目基于化学链氧化-还原过程，选择以廉价的复合过渡金属氧化物作为氧载体，以特定结构控制其晶格氧活性物种实现丙烷制丙烯的选择性氧化脱氢反应，克服无氧脱氢过程受限于热力学平衡和催化剂积碳失活、以及有氧脱氢过程深度氧化的问题。围绕控制氧载体的晶格氧含量、种类及储放效率，厘清晶格氧迁移过程及丙烷C-H键活化过程的本质机理，提高其反应活性、选择性和稳定性等关键科学问题，发展高效的丙烷氧化脱氢反应过程。通过精准调控氧载体的特定组成与结构，结合联用或原位谱学表征技术，建立准确的结构-性能对应关系，辅以原子尺度理论计算研究，从材料合成、构效关联及机理研究三个层面上加深对化学链反应过程的认识，开发具有优异反应性能的金属氧化物氧载体材料。

本项目开发了基于廉价过渡金属氧化物的多种多相催化剂及氧载体材料，应用于丙烷脱氢制丙烯反应，系统开展了催化剂构效关系及催化机理相关方面的研究，取得了以下主要结果：.（1）在二元Mg-Fe-O系统相图指导下，通过球磨辅助固态合成法构筑了具有MgxFe1-xO岩盐和Mg1-yFe2+yO4尖晶石固溶体共存的复合氧化物结构，相较传统FeOx氧载体，其载氧量及化学链氧化-还原循环稳定性显著提升。.（2）利用γ-Al2O3纳米片状载体稳定化孤立的四配位Co2+活性位，在丙烷脱氢反应中显示出>97%丙烯选择性及>16 mmol g-1 h-1较高活性。进一步掺杂Si4+助剂，有效调控了催化剂表面Lewis和Bronsted酸性质，调变了丙烯的吸附构型与脱附性质，增强了Si-Co-Al2O3催化剂的抗积碳稳定性。.（3）开发了具有超短三维孔道结构及丰富氧缺陷位点的纳米网状SiO2载体，能够分散并锚定单原子分散的Co1-O3活性位，能够实现95%丙烯选择性及高达196 h-1本征活性。.（4）以Co@MCM-41作为模型催化剂，在不同条件下进行预还原处理，实现了骨架Co2+离子向骨架外单分散Co0、纳米团簇及颗粒的多阶段迁移，进而探讨了Co活性位点结构与丙烷脱氢性能、丙烯相互作用以及积碳过程之间的构效关系。.（5）系统性综述了关于金属和金属氧化物催化丙烷脱氢制丙烯反应过程的构效关系及催化机理的最新研究进展。