碳包覆铜纳米粒子限域型催化剂的构建及其性能研究

Dimethyl carbonate (DMC) is one of important green chemical products in China's coal chemical industry. Recent research reveals that the activated carbon supported Cu nanoparticles show good catalytic performance in the synthsis of DMC by oxidative carbonylation of methanol. However, the aggregation of Cu nanoparticles during the reaction has become one of the major barriers to commercialization of this new catalyst. In this research, we proposed the fabrication of yolk-shell composites consisted of a Cu nanoparticle core and a hollow porous carbon shell. In the Cu@C composite, the core Cu nanoparticle is entrapped in a medial void space surrounded by the carbon shell. The structural features could lead significant tolerances to aggregation with neighboring nanoparticles. Moreover, since the void space provides specific microenvironments suitable for the catalytic reaction, excellent catalytic activity and stability for the oxidative carbonylation of methanol is expected to be obtained. The main components of this research proposal are as follows: The formation, encapsulation and distribution of Cu nanoparticles within the carbon shell is explored, the catalytic mechanism for the oxidative carbonylation of methanol to DMC over Cu nanoparticles is discussed, the chemical process and mechanism of the fabrication of Cu@C by assembly method is clarified, the influence of preparation parameters on the structure and catalytic performance of Cu@C is discovered,and superior catalytic performance is expected to be obtained as compared to the Cu/AC catalyst prepared by conventional techniques. All above results will provide the scientific foundation for the preparation of high efficient catalysts for clean synthesis of DMC.

碳酸二甲酯（DMC）是我国煤化工领域重点开发的下游绿色化学品，活性炭负载纳米铜催化剂Cu/AC在甲醇气相氧化羰基合成DMC中反应活性很高，但由于高度分散的铜纳米晶体表面能高，在反应过程中容易发生团聚，极大地制约了催化剂性能。本项目采用"先壳后核"法组装合成摇铃式碳包覆纳米铜粒子催化剂Cu@C，旨在利用特殊的限域性结构体系限制铜纳米粒子聚集，提供适于催化反应特定的微化学环境，进而获得理想的催化性能。主要内容包括：探讨碳壳及铜纳米粒子形成、组装过程、分布状态及其相互作用，阐明制备化学过程与机制；分析反应物分子在催化剂微观结构的传递过程、相互作用规律以及化学环境的变化，建立多尺度范围内催化剂活性与结构的定量关系；明确催化活性中心的本征结构，探明催化作用机理，建立详细反应动力学模型，揭示"纳米限域效应"的催化调控基础及其在催化剂设计中的作用，为制备高性能DMC合成催化剂奠定理论与实践基础。

碳负载铜催化剂（Cu/C）在甲醇氧化羰基合成碳酸二甲酯（DMC）反应中会发生铜纳米粒子的团聚现象，极大地限制了催化性能。本项目通过构筑核壳型中空碳球包覆纳米铜粒子催化剂，借助限域效应改善反应活性和稳定性，进而获得理想的催化效果。主要研究内容和结果如下：.（1）采用“先壳后核”策略组装制备了摇铃型碳包覆纳米铜（Cu@C）催化剂，碳球平均尺寸约210 nm，空腔尺寸约80 nm；采用KOH活化可以增加碳壳的孔隙率，通过改变铜盐浓度能够调控内核Cu纳米粒子的尺寸（30~55 nm）；Cu@C在催化合成DMC反应中，甲醇转化率达到17.1%，TOF值为8.6 h-1，经过7次循环反应后活性仅发生轻微下降，铜纳米粒子未没有发生流失；此外，在碳壳中掺杂氮元素可以进一步改善了催化活性和稳定性；.（2）建立了“一步共热解”合成摇铃型Cu@Carbon催化剂的方法，其中采用油酸铜同时作为有机金属前驱体和成型过程中的软模板，通过改变制备参数可以调控碳球尺寸（330-390 nm）和腔体尺寸（190-220nm）；Cu@Carbon在催化合成DMC反应中经过5次循环后活性没有发生下降，仍然保持了高选择性，多孔碳壳能够阻止活性金属的团聚及流失，同时具有足够的渗透性，可以使反应物与活性金属表面发生充分接触；.（3）采用其他碳基材料包括活性炭、有序介孔碳、氧化石墨烯和碳气凝胶负载金属铜用于DMC合成反应，探讨了微波加热、炭黑插层、氮掺杂及KOH活化对催化剂性能的影响，采用DFT计算方法研究了不同结构的炭负载铜催化剂上甲醇氧化羰基化反应机理，为DMC的清洁合成奠定了科学基础；.（4）“一步共热解法”具有很好的普适性，可以制备出具有不同内核组分的摇铃型纳米复合材料（如ZnO，NiO），这些材料均表现出较好热稳定性，本方法为碳包覆纳米复合材料的设计开辟了新的合成策略，广泛适用于催化、制药、锂电池和化学传感器等领域。