石墨烯包覆钴催化乙酰丙酸水相加氢制备1,4-戊二醇

A variety of carboxyl-containing platform chemicals have been emerged with the rapid development of biomass conversion. These bio-based carboxylic acids can undergo catalytic hydrogenation to produce valuable diols that are monomers of polyester. Nevertheless, the current production methods suffer from several drawbacks including low yield, using homogenous and noble metal catalysts, as well as the limited exploration for reaction mechanism owing to the strong acidic and hard reducible carboxyl group. Thus, this project selects aqueous hydrogenation of levulinic acid to 1,4-pentanediol as a model reaction, and designs a hydrothermal stable non-noble metal Co-based catalyst encapsulated in N-doped graphene (Co@NG). The key scientific problem will be focused on the reaction mechanism of catalytic carboxylic acid hydrogenation in graphene confined nanoreactors. The following contents are included. (1) A series of Co@NG catalysts with tunable N content and graphene layers are fabricated by pyrolysis of the precursor metal-organic framework materials. (2) The structure-behavior relationship between microstructure of Co@NG and intrinsic activity is correlated based on characterization and evaluation results. (3) The surface reaction mechanism in graphene confined catalysis is elucidated by in situ FTIR and EXAFS combined with theoretical calculation of quantum chemistry. The monodispersed Co@NG will be fabricated, in which its shell is consisted of 2-5 graphene layers. Co@NG will obtain more than 95% yield of 1,4-pentanediol and 200 h long-term performance. The project in the present work will provide theoretic and practical guidance for the sustainable production of valuable diols from the catalytic hydrogenation of bio-based carboxylic acids.

随着生物质转化领域的快速发展，涌现了一大批含有羧基官能团的平台化学品，这些羧酸通过催化加氢能够合成重要的聚酯单体二元醇。由于羧酸的强酸性且很难还原，该反应收率低、采用均相和贵金属催化剂和对反应机理研究很少。基于此，本项目以乙酰丙酸水相加氢制备1,4-戊二醇为模型反应，构建水相稳定的氮掺杂石墨烯包覆的非贵金属Co基催化剂（Co@NG），着重研究关键科学问题石墨烯限域空间内羧酸催化加氢的表面反应机理。主要内容包括：（1）以金属有机框架材料为前驱体热解制备氮含量和石墨烯层数可调的Co@NG；（2）建立Co@NG的微观结构与本征活性之间的构效关系；（3）结合原位FTIR、EXAFS以及量化理论计算，阐述石墨烯限域空间内乙酰丙酸的扩散和反应机理。预期Co@NG壳层石墨烯层数控制在2‒5层，1,4-戊二醇收率≥95%，催化剂寿命≥200 h。本项目的实施将为生物质基羧酸高效催化加氢提供理论和实践借鉴。

生物质衍生物羧酸是重要的平台化学品。其中，乙酰丙酸加氢制备1,4-戊二醇具有重要的应用前景和理论价值。由于羧酸具有强酸性且很难还原，目前该工艺过程存在一些问题，如采用均相和贵金属催化剂、催化剂容易失活和反应机理研究较少等。针对上述问题，本项目以金属有机骨架材料材料为前驱体热解制备N掺杂石墨烯包覆的六方密堆Co催化剂（hcp-Co@G），石墨烯的层数仅为2~5层。由于壳层石墨烯的保护作用，该Co纳米粒子能够抵御乙酰丙酸的腐蚀，在反应过程中非常稳定，能够重复使用6次。由于石墨烯的限阈催化效应，显著提升了乙酰丙酸加氢的反应活性。400 °C热解制备的催化剂hcp-Co@G400在很多含不同官能团的羧酸加氢反应中获得了优异的反应性能和稳定性。而且，其转换频率比传统的面心立方体Co催化剂高一个数量级。结合原位漫反射红外光谱等表征并结合量化理论计算，对其限阈催化反应机理进行深入揭示，羧酸首先发生脱羟基形成RCH2CO*，然后再加氢形成RCH2COH*，最后再连续加氢生成醇。项目实施过程中，在Applied Catalysis B: Environmental、Journal of Catalysis和Catalysis Science & Technology等发表生物质转化相关SCI论文9篇。本项目的成功实施将为生物质选择性加氢转化为高附加值产品提供理论和和实践借鉴。