双功能核壳催化剂的吸附性质及其糠醛加氢脱氧性能研究

Furfural has recently been identified as one of the most important biomass-derived platform chemicals. The selective transformation of furfural to 2-methylfuran, a valuable biofuel and chemical, is of great significance. Literature research proposed that the conversion of furfural to 2-methyfuran proceeded through 2 steps, the hydrogenation of furfural to produce furfuryl alcohol, and the subsequent hydrodeoxygenation of furfuryl alcohol to produce 2-methylfuran. This proposal plans to synthesize bifunctional furfural hydrogenation catalysts containing two types of active centers, namely bimetallic overlayer structure and oxygen vacancies, to study the reaction process of furfural hydrogenation to furfuryl alcohol, and furfuryl alcohol hydrodeoxygenation to 2-methylfuran, respectively. Special research attention will be paid to the effect and mechanism of adsorption properties on catalyst reactivity in furfural hydrogenation. Firstly, the adsorption strength and the furfural adsorption configuration on overlayer catalysts will be studied. Afterwards, the reactivity and selectivity in furfural hydrogenation of overlayer catalysts will be tested and Langmuir-Hinshelwood kinetic models of furfural hydrogenation to furfuryl alcohol will be established. The mechanisms of how catalysts’ adsorption strength influences their furfural hydrogenation reactivity will be clarified. The furfural adsorption configuration will be correlated with reaction mechanism and product selectivity. Copper supported on oxides with various concentration of oxygen vacancies will be synthesized and studied in the furfuryl alcohol hydrodeoxygenation. The relationship between oxygen vacancy concentrations and 2-methylfuran productivity will be established and interpreted. Finally, the bifunctional catalysts with both active centers will be studied, to provide solid basis for future furfural hydrogenation catalyst design.

糠醛是重要的生物质平台化合物，将糠醛转化为应用前景广阔的2-甲基呋喃有重要意义。已有研究指出糠醛制2-甲基呋喃过程可分解为糠醛加氢制糠醇、及糠醇加氢脱氧制2-甲基呋喃两步反应。本项目拟制备双金属核壳结构与氧空位耦合的双功能催化剂，分别研究两种活性中心对两步反应的催化过程，并重点关注核壳催化剂的吸附性质对其糠醛加氢制糠醇催化性能的作用规律这一科学问题。首先测定核壳催化剂吸附强度，研究糠醛在其表面的吸附模式，考察核壳催化剂的糠醛加氢制糠醇催化性能，建立反应动力学模型，阐明催化剂的吸附强度与糠醛转化速率的相关性及原理，以及糠醛吸附模式对糠醛加氢反应机理、产物选择性的作用机制。其次制备氧空位浓度可调控的氧化物负载铜催化剂用于糠醇脱氧制2-甲基呋喃，探究氧空位浓度、性质与糠醇脱氧反应速率的关系。最后研究核壳结构与氧空位耦合的双功能催化剂的催化性能，为糠醛加氢制2-甲基呋喃催化剂的设计提供科学依据。

糠醛作为来源于非粮生物质的重要有机化工原料，其向碳五化学品的高效转化可以降低化石资源消耗，提高生物质资源利用效率。本项目制备了双金属核壳结构与氧空位耦合的双功能催化剂，并重点关注核壳催化剂的吸附性质对其糠醛加氢制糠醇催化性能的作用规律这一科学问题。研究发现，双金属核壳催化剂在糠醛加氢反应中转化频率显著高于单金属催化剂和用共浸渍法制备的合金催化剂。通过实验数据与反应动力学模型的拟合，证明了核壳催化剂具有适中的吸附强度，这种适中的吸附强度更有助于反应物的吸附与产物的脱附，提高了催化剂的催化活性。此外，通过比较不同催化剂在不同条件下的2－甲基呋喃选择性，我们还发现催化剂的氧空位浓度对于2－甲基呋喃的选择性有重要影响，通过考察不同氧化物负载的钴催化剂的糠醛制2－甲基呋喃性能后发现，催化剂的路易斯酸中心数量与2－甲基呋喃的生成速率呈线性关系。这一发现表明路易斯酸中心直接参与了糠醛的脱氧反应，起到了活性中心的作用，且通过以糠醇为反应物的对比实验证明了糠醛加氢脱氧生成2－甲基呋喃的反应有多种可能路径。此外，本项目还研究了糠醛加氢制备2－甲基四氢呋喃中的非贵金属催化剂，通过两级串联催化实现了糠醛的一步法加氢制2－甲基四氢呋喃，2－甲基四氢呋喃收率最高可达87%。这一过程可分为两步：糠醛首先在钴催化剂的作用下转化为2－甲基呋喃，随后2－甲基呋喃被镍催化剂转化为最终产物2－甲基四氢呋喃。最后对糠醛加氢中碳损失及催化剂失活的机制进行了研究。结果表明，酸性载体的铜基催化剂积碳严重，形成大量低聚物，催化剂失活较快；而碱性载体更有利于抑制积碳，反应物的利用率更高。通过本项目的研究，为糠醛的高值利用及高效糠醛加氢催化剂的设计奠定了基础。