纤维素及其衍生物催化转化制有机酸的研究

Catalytic conversion of cellulose, the most abundant renewable biomass resources, into platform molecules is helpful for establishing a sustainable society. It is one of the most promising routes for conversion of cellulose under non-hydrogen conditions to obtain important organic acids, which contain similar chemical composite with cellulose. From view point of scientific study, we will intensively study the activation and cleavages of chemical bonds in cellulose, including the broken of glycolic bond (via hydrolysis) and C-C bond cleavage (via retro-aldol, or oxidative-cleavage, or oxidative decarboxylic) etc, and build up several efficient catalytic systems for cellulose or raw biomass transformations. To be specific, we will firstly develop several solid acids with good stability under hydrothermal conditions, and then based on the candidate solid acids, we will design and prepare three kinds of multi-functional catalysts that could perform the functions of hydrolysis/isomerization/retro-aldol, hydrolysis/oxidative cleaving C-C bond and hydrolysis/oxidation, respectively. These catalysts will be employed to the anaerobic conversion of cellulose to lactic acid and the aerobic transformation of cellulose into formic acid or gluconic acid, respectively. The effects of catalyst structure on the catalytic performances will be investigated carefully for establishing a reliable correlation between the structure and the performances. We will also endeavor to investigate the mechanism of cellulose conversion by studying glucose and cellobiose through theoretical calculations and intended experimental studies. We believe that these studies will greatly contribute to the basic understanding of the activation and cleavage of chemical bonds in cellulose and the key factors influencing the selectivity, and will also provide a novel route for efficient conversion of cellulose.

研究转化丰富的可再生纤维素制平台化合物的反应规律，开发高效催化体系有助于实现建立可持续发展社会的战略目标。其中，在非氢条件下将纤维素转化为与其化学组分相似的有机酸是纤维素转化中最为合理的路径之一。本项目关注纤维素转化反应中糖苷键断裂(水解)、C-C键的断裂(反羟醛缩合，氧化断键)等重要步骤，研究纤维素在惰性或氧气氛下的催化断键规律，建立纤维素乃至真实生物质转化制特定有机酸的高效催化体系。项目拟先研制稳定的固体酸材料，并以此为基础分别构建具有水解/异构/反羟醛缩合、水解/氧化C-C断键和水解/氧化等多功能催化剂体系，实现纤维素无氧制乳酸和氧化制甲酸及葡萄糖酸的高选择性转化。研究各多功能催化剂的结构要素对催化性能的影响，系统认识结构和性能的关系。以葡萄糖，纤维二糖为研究对象，从理论模拟和实验研究反应中的转化机理，探明断键规律和影响选择性的关键因素，为合理设计纤维素高效催化转化体系提供科学思路。

利用丰富的可再生生物质资源生产化学品和燃料对建立可持续发展社会极为重要。因生物质含氧量高，发展高效催化体系将其转化为重要的含氧化学品比如有机酸是最符合原子经济性的策略之一。本项目选择生物质中含量丰富的纤维素及其衍生物为原料，构建了几个多功能催化体系分别将纤维素或其衍生物转化为乳酸、葡萄糖二酸、己二酸和氨基酸等。（a）发展了简单、高效的Sn(II)-Al(III)双离子体系催化纤维素、葡萄糖、果糖等相关生物质高选择性转化制乳酸，在优化的条件下乳酸收率分别达到65%，81%和90%。实验结合理论计算研究表明纤维素制乳酸涉及葡萄糖异构和果糖反羟醛断C-C键等关键步骤。Al(III)主要催化异构反应，而Sn(II)则负责反羟醛缩合，将两者组合可实现异构-反羟醛等多功能耦合，高效催化纤维素转化制乳酸。（b）研制了碳纳米管负载Pt催化剂(Pt/CNT)并用以催化葡萄糖选择氧化制葡萄糖二酸。相比其它负载型Pt催化剂，Pt/CNT对中间产物葡萄糖酸吸附能力更弱，避免了深度降解反应，因此表现出高的葡萄糖二酸选择性。调控溶剂pH值，脱羧等副反应也可得到抑制，在弱碱条件(pH=9)，葡萄糖二酸收率达到81%。（c）葡萄糖二酸高效脱除四个羟基可以获得重要聚合物单体己二酸。发展了氧化锆负载铼催化剂(ReOx/ZrO2)，通过脱水/还原反应高效地脱除葡萄糖二酸多羟基制得相应的链式二烯烃及环式单烯烃。其中后者环上具有共轭结构，开环困难，剩余羟基难以完全脱除。耦合ReOx/ZrO2和Pd/C催化剂，促进了环式单烯烃产物开环及进一步脱羟基，最终得到己二酸酯（收率~66%）。这一步的实现打通了从纤维素到己二酸的生物质合成新路线。（d）发展了一种从木质纤维素经羟基羧酸选择胺化反应制氨基酸的可持续化学合成方法。以乳酸转化为例，我们研制的Ru/CNT在氨水中高选择性将乳酸转化为丙氨酸。机理研究表明乳酸中羟基脱氢是反应决速步，Ru较其它贵金属（Pt，Pd）在NH3存在时脱氢活性更高，因而性能更优异。该催化体系具有普适性，可用于其它生物质衍生的羟基羧酸转化制相应的氨基酸。