甲酸为替代氢源对生物油中酚类组分加氢的研究

Renewable energy sources such as lignocellulosic biomass provide an attractive source of renewable carbon that can be sustainably converted into fuels and chemicals, allowing for a reduction in the need for fossil fuels and a net reduction in the amount of CO2 emitted. One promising way is to produce bio oil by fast pyrolysis, with yield of 65-70%. However, it remains a great challenge to store and convert bio oil because of its high unstability and tendency to form coke during reaction. By hydrogenation under mild condition, the H/C ratio and stability of bio-oil can be significantly improved. The hydrogenated bio-oil can then be used as a potential source in FCC process. Hopefully, it will be able to substantially replace fossil fuel in the near future. Unfortunately, the high cost of H2 resulted from its production, compression and tranportation makes the hydrogenation process non-economical. Hence, the biomass conversion technology using H2 is not competitive at this stage. Apparently, it is highly disirable to find alternative hydrogen sources instead of gas phase H2 for the pratical application of hydrogenation process. For instance, methanol and formic acid have been considered as potential condidates for biomass upgrading. Formic acid, one of the components in bio-oil, can decompose under mild condition and thus act as a safe and efficient hydrogen source. In this proposal, the hydrogenation of phenolic compounds in bio-oil using formic acid as alternative hydrogen source will be explored. Ideally, the catalyst needs to be very active and stable under hydrothermal conditions to fulfill this challenging objective. Recently it has been reported that Cr-MIL-101, one of the metal organic framework materials, supported palladium catalyst shows activity superior to palladium supported on conventional supports for phenol hydrogenation using gas phase H2. Therefore this catalyst will be adopted in this work to test the activity of phenol hydrogenation by formic acid. The research will focus on the effect of different metal centers and organic ligands on the dispersion of palladium nanoparticles and their catalytic activities. The main challenge in this study is to decrease the palladium loading whereas retain the desired activity and reusability. The presence of organic and/or inorganic impurities in bio-oil and the hydrogenation efficiency of formic acid will also be investigated for its potential industrial application.

生物质催化转化关系到国家能源安全与可持续发展。快速热解方法可将木质纤维素类生物质高效转化为生物油(bio-oil)，其产率高达70%。生物油化学稳定性差，很难被直接加工。通过温和条件下适度加氢，可提高油品稳定性，与当前FCC过程耦合，部分或完全替代石油。然而，以氢气作为氢源存在安全性差及成本高的弊端，寻求廉价安全的替代氢源对生物质加氢走向实际工业应用具有重要意义。本研究提出以甲酸为替代氢源，Pd/MIL为催化剂，在温和条件下对酚类组分进行催化加氢，达到将生物油稳定化和提质的目的。项目拟合成具有不同结构特点的MIL材料，如孔道尺寸、金属Lewis酸强度及亲水-疏水性质。研究Pd/MIL催化剂上甲酸分解与苯酚加氢的协同性，探索反应中甲酸的利用效率。揭示MIL材料的性质对负载Pd催化剂反应性能的调控机制。获得加氢活性高，寿命长，抗中毒，能够用于真实生物油中酚类组分低温加氢的高效廉价催化剂。

生物质是自然界中最重要的一类可再生碳资源，将其清洁高效地转化为重要化学品和能源产品是绿色碳科学理念的必然选择。本项目针对木质纤维素衍生物的开发与利用开展了一些探索性的基础研究，以苯酚、糠醛、乙酰丙酸乙酯等几种常见含氧生物质衍生物为模型化合物，考察了载体结构/酸碱性与负载金属纳米粒子在C=O、酯交换、C=C等功能基团协同催化中的构效关系，主要内容包括：.（1）揭示了MIL-101及MIL-53两种金属有机骨架材料的物理化学性质（如孔径、孔道亲疏水性等）对负载Pd纳米粒子的影响规律，发现亲水性强的表面（MIL-101）有利于Pd纳米粒子的高度分散，从而得到高活性负载Pd加氢催化剂。进一步地，通过在MIL-53骨架上引入不同配位基团（NO2、Cl、NH2、OCH3），在调变该材料亲水/疏水性能的同时，实现了骨架基团上电子密度的调变及对负载Pd中心加氢能力及选择性的控制。.（2）通过改变Zr-MOF骨架结构中芳环的数目及骨架拓扑结构，实现了对金属Ru纳米粒子氧化态的调控，确认金属态Ru纳米粒子对糠醛加氢（C=O加氢）具有特异活性。.（3）系统考察了多常见载体负载Pd催化剂在甲酸为氢源对上述几种化合物的氢转移性能，结果表明Pd/TiO2-AC催化剂能够实现甲酸分解及苯酚加氢的耦合，高效催化苯酚氢转移反应。令人意外的是，以甲酸为氢源，负载Pd催化剂对上述另外两种底物均没有较好的催化活性，我们推测甲酸的强吸附能力抑制了氢转移。另外，由于甲酸具有较强的酸性和挥发性，对高温高压反应釜具有很强的腐蚀性能，因此，不适合较高温度下生物质衍生物的催化转化。.（4）发展了一种Nb2O5/C酸性载体负载Pd催化剂，在水相中实现H2活化、C=O加氢、内酯化的一步协同反应，首次报道了较低温度下Pd催化剂上戊内酯的制备。进一步地，利用磺酸功能化的Cr-MIL-101材料负载Pd催化剂，实现了伽马戊内酯在乙醇中的开环-脱水-加氢一锅反应制备戊酸乙酯及戊烯酸乙酯等燃油添加组分。