二氧化碳氧化转化的分子活化机制及资源化利用的关键科学问题研究

The production of chemicals and fuels by using the greenhouse gas of the carbon dioxide as a cheap and clean carbon source is the ideal method to mitigate the carbon dioxide emissions. Among the available routes such as solar and electrochemical methods, the heterogeneous catalytic utilization of the carbon dioxide is more favorable due to its large scale and higher efficiency. However, it is still a challenge since that the carbon dioxide molecule is very stable and is difficult to react. From the linear molecular structure of the carbon dioxide, the carbon atom is prone to accepting electron due to the larger difference of the electronegativity between the carbon and oxygen atoms. Thus, the carbon dioxide shows a certain oxidative ability, which can be used as a soft oxidant. The oxidative dehydrogenation of lower alkanes by using the carbon dioxide as a soft oxidant (CO2-ODLA) has the merits of the high selectivity of lower alkenes, energy saving, and environmentally benign in comparison with the traditional catalytic dehydrogenation process. However, the serious shortcomings of the CO2-ODLA are the low conversion of the carbon dioxide and the fast deactivation of the reported catalysts. From our understanding on the soft oxidative property of the carbon dioxide and the redox nature of the reaction system, this proposal will focus on the following work, i.e., (1) Studying on the adsorption and activation of the carbon dioxide over different catalysts by using the DFT method; (2) Investigating the interfacial effect between different components of the catalyst and proposing the reaction mechanism of the titled reaction; (3) Designing and manufacturing the structured catalyst for the CO2-ODLA in a large scale; (4) Evaluating the feasibility of the dehydrogenation of the lower alkanes by directly using the flue gas; (5) Exploring new catalytic system to efficiently convert methane and carbon dioxide to C2+ hydrocarbons and oxygenates. With the achievements of the project, the industrial technology of CO2-ODLA based on the high-performance catalyst is expected.

将温室气体CO2作为清洁廉价的碳资源转化利用是CO2减排的理想出路，其中非均相催化更有明显优势，但热力学稳定和动力学惰性CO2分子的活化面临巨大挑战。CO2分子中C原子易于接受电子，表现出一定的氧化性。作为弱氧化剂，CO2氧化低碳烷烃脱氢具有烯烃选择性高、节能和环境友好的优点，但现有催化剂普遍存在CO2转化率低和失活迅速等难题。基于CO2的弱氧化性及反应体系的氧化还原特点，本项目从CO2分子活化和氧化还原平衡进行催化剂设计，采用DFT计算、原子层沉积和原位表征等手段，开展（1）CO2及低碳烷烃分子吸附和活化的理论化学；（2）催化剂的界面效应及CO2作为弱氧化剂的反应机理；（3）CO2氧化低碳烷烃脱氢结构化催化剂设计及规模化制备；（4）热电厂烟道气用于低碳烷烃脱氢的可行性及放大；（5）CO2氧化CH4新过程及其催化剂体系等研究，以期建立以新结构化催化剂为核心技术的CO2氧化资源化利用新工艺。

二氧化碳作为弱氧化剂用于丙烷等低碳烷烃氧化脱氢制备高附加值低碳烯烃，不仅能够克服低碳烷烃直接脱氢制低碳烯烃工业化工艺存在的设备投资高、能耗高和原料处理能力较低等问题，而且实现了温室气体CO2的资源化利用，有望成为一条节能且环境友好的绿色合成工艺。但热力学稳定、动力学惰性CO2分子的催化活化面临巨大挑战，现有催化剂普遍存在CO2转化率低和失活迅速等难题。. 本项目针对CO2存在下低碳烷烃C-H键的选择性活化机制、CO2氧化低碳烷烃脱氢（CO2-ODP）的高效催化剂及其界面效应等两个关键科学问题，提出了强化二氧化碳分子C=O键的活化、促进丙烷分子C-H键活化并抑制C-C键断裂的催化剂设计思路，开展了CO2和丙烷的协同活化规律、可还原氧化物（复合氧化物）结构与其催化CO2-ODP性能关系、贵金属与可还原氧化物之间的协同效应、作用机制及其催化CO2-ODP性能等研究，揭示了CO2对CrOx/Al2O3催化CO2-ODP抑制作用的本质原因；发现Pd、Au、Co等金属或GaN、ZnO、In2O3等电子型半导体能够促进CO2分子中C=O键的活化转化、提高负载VOx、CrOx等氧化物催化CO2-ODP的性能，初步阐明了相关作用机理；明确了VOx、CrOx、CeO2、Ce1-xZrxO2和ZnxZr1-xO2-x固溶体等重要可还原氧化物的结构与其催化CO2-ODP性能之间的关系，揭示了活性中心的结构，提出了反应机理；设计了PtSn/CeO2/SiO2、Pt-In/SiO2等高性能CO2-ODP催化剂，厘清了贵金属与缺陷氧化物之间的协同作用及其影响CO2-ODP催化性能的作用机制；基于RhPt@Zn-MFI分子筛中孤立的Zn2+活性位点和高分散贵金属纳米颗粒之间的协同效应，显著提升了其催化CO2-ODP的活性和稳定性。. 上述创新性结果已在Nature Commun., Appl. Catal. B, J. Catal., Ind. Eng. Chem. Res.等刊物发表论文53篇，申请中国发明专利5件，其中授权1件，为发展以高性能催化剂为核心技术的CO2氧化低碳烷烃脱氢制低碳烯烃绿色工艺奠定了基础。同时，基于上述认识提出的CO2临氢氧化丙烷脱氢制丙烯和合成气工艺及催化剂、提高氧化物催化剂性能等技术，表现出良好的工业应用前景。