燃油深度氧化脱硫高效固载多层离子液体催化剂构筑及反应动力学研究

The oxidative desulfurization (ODS) of liquid fuels such as gasoline and diesel with hydrogen peroxide is promising as an energy-saving and environmentally benign route alternative to the conventional hydrodesulfurization process, and the design of a high-performance catalyst is the key issue. Based on our preliminary results of the selective oxidation of different substrates catalyzed by SiO2-supported bilayer ionic liquid (IL) and phosphotungstic acid, this project aims to design a series of SiO2-supported multilayered ionic liquid and heteropoly acid catalysts (SiO2-MIL-HPA) for ODS with hydrogen peroxide, which combine the merits of the high activity of the homogeneous catalyst and the easy separation of the solid catalyst. The SiO2-MIL-HPA will be constructed by considering the impact of the parameters such as the structural and porous properties of SiO2, the length of the carbon chain, the terminal alkyl group of the imidazole, and the number of the layers of the ionic liquid (IL), the density of the immobilized IL over SiO2, and the type of the heteropoly acid. The activity and recycling number of the SiO2-MIL-HPA for ODS with hydrogen peroxide will be evaluated, and the diffusional behavior of reactants, kinetics, and mechanism of the titled reaction will be studied. Combining these results and the characterization data of the fresh and used catalysts, the impact of the synergetic effect between the HPA and multilayered IL, structural and hydrophilic/hydrophobic properties, and the distribution of the active sites over SiO2-MIL-HPA on the catalytic performance will be addressed. The detailed reaction mechanism will be proposed together with the results of the kinetic equation and the in-situ FT-IR monitoring of the adsorption, activation and reaction of the S-containing model compounds over different catalysts. Finally, a reasonable model of the high-performance SiO2-MIL-HPA for the titled reaction will be given. The achievement of the project will be valuable for the development of a high-performance catalyst for the ODS of liquid fuels with hydrogen peroxide.

双氧水氧化燃油深度脱硫有望成为一条节能且环境友好的绿色脱硫工艺，但高效催化剂设计是其关键。在SiO2固载双层离子液体-磷钨酸催化选择性氧化创新性前期研究基础上，结合均相催化剂高活性和固体催化剂易分离的优点，本项目提出从SiO2的结构和孔尺寸、离子液体结构（咪唑间碳链长度和咪唑封端基）、层数和嫁接密度、杂多酸种类等角度，设计构筑SiO2-多层离子液体-杂多酸（SiO2-MIL-HPA）催化剂，研究其催化双氧水氧化燃油深度脱硫的活性、循环使用性能、扩散效应、动力学和反应机理，在揭示离子液体与杂多酸间的协同效应、SiO2-MIL-HPA的结构、亲/憎水、活性物种分布等影响其催化性能的基础上，结合反应前（后）催化剂的结构、织构等表征、动力学和原位红外跟踪含硫模型化合物在催化剂表面的吸附、活化和反应等结果，提出合理的反应机理，构建相应的催化剂模型，为双氧水氧化燃油深度脱硫高效催化剂的开发奠定基础。

双氧水氧化燃油深度脱硫有望成为一条节能且环境友好的绿色脱硫工艺，但高效催化剂设计是其关键。本项目提出了利用多层离子液体提供的拟均相特征弥补多相催化剂缺陷的设计思路，通过化学键合、离子交换方法，制备了一系列SiO2-多层离子液体-杂多酸（SiO2-MIL-HPA）催化剂；采用FT-IR、TG-DSC、XRD、XPS、低温氮吸附、接触角测量等技术，揭示了催化剂的组成、结构、织构、热稳定性、亲/憎水等性质；采用TEM、STEM/Mapping等技术，明确了催化剂活性组分的分布。利用BT、DBT、4-MDBT、4,6-DMDBT为含硫模型化合物，研究了SiO2-MIL-HPA催化H2O2氧化燃油脱硫的催化活性和循环使用性能。结果表明，SiO2的结构、载体表面羟基数、离子液体结构（咪唑间碳链长度和咪唑封端基）、咪唑层数和嫁接密度、杂多酸种类是影响催化剂催化性能的关键因素；POMs和BiILs的协同作用使催化剂具有三维微环境和高的流动性，便于硫化物和H2O2接近催化剂，从而大大提高了催化效率。SiO2（酸活化）所用质量与3-氯丙基三乙氧基硅烷体积比为1.75:1、咪唑间碳数为四的双层离子液体负载keggin-type磷钨酸催化剂SiO2(50nm)-BiIL-CO2H-PW、SBA15-BiIL-SO3-PW，均可在温和条件下实现四种含硫模型化合物的100%脱除。优化的催化氧化脱硫体系没有明显的工艺放大效应，且催化剂在模拟油（BT）为500 mL时，循环使用多次催化活性没有降低。结合反应前（后）催化剂的结构、织构等表征分析，提出了负载多层离子液体-杂多酸催化双氧水氧化脱硫的反应机理。根据上述结果，获得了高活性和循环使用性能优异的固载双层离子液体-杂多酸催化剂，为双氧水氧化燃油深度脱硫高效催化剂的开发奠定了基础。