氮掺杂寡层石墨烯包覆纳米铜催化剂的构筑及其性能研究

Methyl glycolate (MG) is one of high added-value downstream products in coal chemical industry. During the synthesis of MG by hydrogenation of dimethyl oxalate (DMO), the chemical state of Cu species dynamically and cyclically evolves. Such evolution results in the aggregation of Cu nanoparticles and the decreased active specific surface areas of Cu(I) and Cu(0), consequently decreases the catalytic activity and selectivity towards MG. In this research, we proposed the fabrication of ultrathin N-doped graphene wrapped Cu nanoparticles (Cu@NG) catalyst by one step co-pyrolysis process. The confinement effect caused by N-doped graphene shell could effectively restrict the agglomeration of Cu nanoparticles and provide a suitable microenvironment for the catalytic reaction. Additionally, the appropriate ratio between Cu(I) and Cu(0), as a crucial factor for DMO hydrogenation and selective hydrogenation of acyl group, could be effectively maintained by the electronic effect caused by nitrogen doping. The main contents of this research proposal are as follows. The chemical mechanism of fabricating Cu@NG catalyst of by one step co-pyrolysis method will be clearly illustrated. The interaction between Cu nanoparticles and N-doped graphene, the spatial and electronic structure of the catalyst will be explored. The influence of preparation parameters and the amounts of doping nitrogen on the structure and the distribution of active Cu sites, which have significant effect on the catalytic performance of Cu@NG catalyst, are going to be discovered. The catalytic mechanism for the hydrogenation of DMO to MG over Cu catalyst will be well discussed and clarified. All above results will provide the scientific foundation for the preparation of high efficient catalysts for clean and efficient production of MG.

乙醇酸甲酯（MG）是一种高附加值的煤化工下游化学品，在草酸二甲酯加氢合成MG反应中，铜催化剂的化学态处于频繁的氧化还原循环变化中，导致团聚及Cu(I)和Cu(0)活性比表面积降低，制约了催化活性和选择性。本项目采用一步共热解法组装合成氮掺杂寡层石墨烯包覆纳米铜催化剂Cu@NG，利用特殊的限域结构抑制铜纳米粒子聚集长大，提供适于反应的微化学环境；借助氮原子的电子效应稳定活性铜物种，保持适宜的Cu(I)/Cu(0)比值，调控酰基的加氢程度，获得理想的催化性能。主要内容包括：探讨氮掺杂石墨烯与铜纳米粒子的组装过程、相互作用及空间结构和电子结构；阐明制备参数及氮掺杂对活性铜物种分布状态的影响；分析反应物分子在催化剂微观结构中的传递过程及相互作用规律，明确催化剂构效关系及催化活性中心的本征结构；探明催化作用机理，揭示“限域效应”的调控基础及其在催化剂设计中作用，为实现MG的清洁高效生产提供科学依据。

在草酸二甲酯加氢合成MG反应中，铜催化剂的化学态处于频繁的氧化还原循环变化中，导致团聚及Cu(I)和Cu(0)活性比表面积降低，制约了催化活性和选择性。本项目采用一步共热解法组装合成炭黑负载氮掺杂寡层石墨烯包覆纳米铜催化剂Cu@NG/C，利用特殊的限域结构抑制铜纳米粒子聚集长大，借助氮原子的电子效应稳定活性铜物种，有效提高了催化剂的稳定性。主要的研究内容和结果如下：.（1）采用一步共热解法组装合成炭黑负载氮掺杂寡层石墨烯包覆纳米铜（Cu@NG/C）催化剂。与比Cu/C催化剂相比，Cu@NG/C表现出更好的催化活性和稳定性，并且其空间限域效应有效避免了铜纳米粒子的团聚、流失和氧化； .（2）研究了氮掺杂石墨烯与铜纳米粒子的组装过程、相互作用及空间结构和电子结构，探讨了催化剂制备过程中铜源与邻菲罗啉比例、共热解温度等工艺条件对催化剂性能的影响，氮掺杂有效地提高铜组分的分散度，并增强了催化剂对反应物分子的吸附； .（3）采用密度泛函理论（DFT）计算方法构建了Cu0、Cu+及Cu0/Cu+复合催化剂模型，分析了DMO、H2、MG分子及中间物种在催化剂上的吸附及解离行为，明确了DMO加氢反应中Cu0与Cu+位点之间的协同作用，发现在Cu+活性位点上，MG的吸附能小于其活化能，Cu+起到稳定MG的作用；.（4）制备了硼掺杂碳气凝胶负载铜催化剂并应用于酯加氢反应中，探讨了硼掺杂对铜催化剂酯加氢性能的影响，适量的硼掺杂提高了铜组分的分散度，并调变了铜物种的价态分布，提高了铜催化剂的加氢活性和稳定性；.（5）以离子树脂为碳源，制备碳微球负载铜纳米颗粒（Cu/CMS）催化剂，利用离子树脂表面的磺酸基团锚固铜纳米颗粒，增强铜组分与碳微球间的相互作用力，提高铜分散度，阻止铜纳米颗粒团聚烧结，改善了催化剂的活性和稳定性。