温和条件下纤维素生物质的绿色水热电催化转化与机制研究

As a cheap and renewable resource, cellulose can be catalytically transformed into the chemicals obtaining a high added value in use, which would become the hot spot of the study in the energy and chemical engineering field. However, the cellulose is hardly hydrolyzed, the key and difficulty of its utilization is how to decrease the high reaction temperature and pressure, and at the same time, increase the catalytical conversion efficiency. In this study, we combined the hydrothermal with electrocatalytical method, in which the electrocatalyst is subsititued for the conventional catalyst. By means of the energy provided by the electron, the temperature and pressure needed can be effectively decreased,which would help to obtain the high reaction efficiency and product selectivity for cellulose conversion under a mild condition. Through controlling the hydrothermal condition, devising the high-efficiency electrocatalytic anode and cathode, adjusting the potential and current, and selecting the suitable reaction media such as the ionic liquid, the cellulose conversion by the hydrothermal and electrocatalytic method is built. In this process, the construction of the electrocatalysts,the way of the electrode reaction, and the choice of the ionic liquid have be fully discussed for the control capability of the product selectivity and the productivity promotion of the objective products. The special physicochemical properties of cellulose in the reaction system, the hydrothermal electrocatalysis characteristic and the current efficiency have also been studied for understanding the dynamic process and the reaction mechanism,especially the synergy mechanism of hydrothermal and electrocatalytic effect. This study has not been reported yet, which will provide a new approach for the catalytic conversion of cellulose.

纤维素是一种廉价的可再生资源，通过催化转化实现高附加值利用，将是能源化工领域的研究热点。但纤维素非常难水解，如何降低高温高压反应条件和提高催化转化效率是目前研究的关键和难点。本项目提出将水热与电催化方法结合，以电催化剂代替传统催化剂，并借助电子提供能量的方式降低纤维素催化转化反应所需的外界条件，将有利于在温和条件下实现反应的高效性和产物的选择性。通过控制水热反应条件，设计高效的阴阳极电催化剂、控制电位和电流及选择合适的反应介质如离子液体等，掌握纤维素水热电催化转化的方法和工艺；探讨电催化剂、电极反应控制方式、离子液体等对产物选择性的调控能力，提高目标产物的产率；研究纤维素在该反应体系下特殊物理和化学性质、水热电催化特征和电流效率、转化产物等，揭示纤维素水热电催化转化的动力学过程和反应机理，并深入探讨水热与电催化反应的协同机制。这一研究工作未见有相关报道，将为生物质催化转化开辟一种新的方法。

本项目将水热氧化和电化学催化方法相联用，建立了一种温和、高效的水热电催化氧化方法。通过选择或制备高水热稳定性、高催化性能的BDD、Pt及Nano-Pt/Ti等电极，将其应用于纤维素和环境污染物等废弃物的处理中，取得了优异的催化转化和降解效果。研究中通过对温和水热反应条件(温度：100~135oC, 初始压力0.3~0.5 MPa)下电极和反应液的物理化学特性的变化分析、对反应体系中活性基团（·OH）数量的监测，对体系中反应速率常数、反应活化能等参数的分析以及对反应体系中各中间体和产物浓度的演变分析，探索了水热反应和电化学反应的协同作用机制。此外，还通过电化学氧化方法，在常温常压下采用设计制备的Nano-Au/碳气凝胶（CA）电极对经浓NaOH冷冻预处理的纤维素溶液进行了选择性催化转化。结果表明，18h内体系中葡萄糖酸的产率高达~68%，总有机酸产率高达89%。通过对电催化电极的基体、纳米金催化剂的特性分析以及对反应条件的考察，探讨了纤维素获得高效选择性催化转化的原因。另外，通过对产物在不同反应时间内的浓度研究，还获得了纤维素在碱性条件下选择性电催化氧化生成葡萄糖酸的机理。