合成气定向转化含氧化合物铜基催化剂的基础研究

Conversion of coal-based syngas into oxygenated compounds, such as methanol, ethanol, ethylene glycol, carbonate ester and etc., is a unique characteristic of coal-based chemical products from syngas (CO+H2) with great development advantage. In recent years, these processes have received much attention for utilizing the O atom in CO molecule and reducing the emissions of CO2 efficiently. All the reactions are preferentially catalyzed by copper-based catalysts. Despite of different composition and structure, all the catalytic active site is dominated by Cu(+) and (or) Cu(0) in copper-based catalysts, which is largely affected by metal promoter or carrier surface. Additionally, all these reactions involve the adsorption and activation for C≡O and H-H bond as well as the activation and hydrogenation for -C(H)=O bond. In this project, we will focus on the oriented synthesis of oxygenated compounds from syngas, such as alcohol, carbonate ester and etc., systematically investigate the common basic theory in the catalytic processes, including the nature of Cu catalytic active center, the regulation of surface structure and composition of the catalysts, to understand the law for the formation and stabilization of Cu active center, the interfacial interaction or synergistic mechanism between Cu active center and metal promoter or carrier. Moreover, we need to study the discipline for adsorption and activation of CO and H2 molecule so as to learn the activation and hydrogenation process of formyl or acyl, and to control the cleavage of C-O bond, the formation and coupling of C-C, C-H as well as O-H bond. And the diffusion effect of the reaction molecules and strengthen cooperation with interfacial interaction are also very important. All the results will guide us to design and control the pore structure of catalysts, and to eventually provide theoretic basis for efficient and oriented conversion of syngas to oxygenated compounds.

煤经合成气催化转化为甲醇、乙醇和乙二醇以及碳酸酯等含氧化合物，能够充分利用CO中氧原子，减少CO2排放，是煤化工产品的重要特征和发展优势。这些反应以Cu基催化剂为主，针对每个反应催化剂的组成和结构不同，然而其催化活性位均以Cu(+)/Cu(0)为主，且都涉及C≡O和H-H吸附活化以及酰基-C(H)=O活化加氢等反应过程。本项目以合成气定向合成醇和酯等含氧化合物为目标，系统研究Cu基催化剂活性中心及其催化作用等共性问题，深入了解Cu活性位的形成和稳定规律、助金属或载体与Cu活性位的表界面效应和协同作用机理，探讨CO和H2吸附和活化规律，阐明酰基中间体的形成和活化加氢过程，获得催化C-O键断裂，C-C键、C-H键和O-H键的形成和控制理论，并研究反应分子在催化剂孔道结构中的扩散效应，揭示表界面催化反应与分子扩散的耦合规律，以设计和调控催化剂微观结构，为合成气高效定向合成含氧化合物提供理论基础。

本项目以合成气定向合成甲醇、乙醇、乙二醇和碳酸酯等含氧化合物为目标，针对Cu催化剂活性中心及催化作用等共性问题，系统研究Cu活性位形成和稳定规律、助剂或载体与Cu表界面效应和协同作用机理，深入了解催化C-O键断裂，C-C键、C-H键和O-H键形成机制，及分子在催化剂孔道中扩散效应和表界面催化反应的耦合规律，为合成气高效定向合成含氧化合物提供理论基础。通过项目研究，发现催化剂前驱体的制备过程，对催化剂微观结构和催化活性影响加大，通过旋蒸沉淀制备的催化剂中，Cu颗粒尺寸小且分布范围窄，有利于抑制催化过程中Cu颗粒的熟化效应，而助剂Al等有利于提高Cu0分散度，提高CO加氢生成甲醇的活性；同晶取代制备的Cu-Co/Ni前驱体晶相结构单一，有利于暴露更多Cu-Co/Ni活性界面，促进乙醇高选择性合成；水解沉淀制备的前驱体中含有更多层状硅酸铜，催化剂具有较大Cu表面积和Cu+/(Cu++Cu0)比例，而添加Ni会形成Cu-Ni活性界面，能显著改善草酸酯和乙二醇加氢催化活性。另外，介孔碳和碳纳米管能够将活性Cu物种限域，抑制焙烧过程中发生团聚，而表面含氮基团还可抑制反应过程中Cu物种的氧化而失活，稳定催化剂的活性和选择性。研究结果还表明，Cu催化CO/H2合成甲醇反应速控步骤为CH2OH+H→CH3OH，能垒为158.9 kJ/mol；Zn掺杂后速控步骤为CO+H→CHO，活化能降低到120.8 kJ/mol；Ga掺杂后速控步骤为CHO+H→CH2O，活化能低至80.5 kJ/mol，显著提高了催化活性。对于甲醇氧化羰基化反应，催化剂表面Cu物种的催化活性顺序为Cu+ > Cu2+ > Cu0，Ca等助剂元素均能降低CO插入反应的能垒，提高催化活性。Cu0和Cu+协同催化乙酸甲酯加氢反应，Cu0活化解离氢气而Cu+吸附活化CH3O*或CH3CO*活性物种。脱硅处理能够使Y分子筛中小笼坍塌，形成新的超笼结构，相邻超笼连接形成丰富的介孔，促进活性物种Cu+落位于超笼内，增强了反应物与活性中心的可接触性，同时，介孔促进了反应物和产物分子的扩散，甲醇氧化羰基化反应活性显著提升。