高分散Cu/SiO2纳米催化剂的超临界可控制备及其在DMO加氢制备乙二醇反应中的应用

Ethylene glycol (EG) is widely used as antifreeze and precursors in the production of polyesters. One of the most promising approach to EG is coal-based production technology via dimethyl oxalate (DMO) hydrogenation. Preparation of highly active catalysts plays a key role in the Ethylene glycol (EG) is widely used as antifreeze and precursors in the production of polyesters. One of the most promising approach to EG is coal-based production technology via dimethyl oxalate (DMO) hydrogenation. Preparation of highly active catalysts plays a key role in the synthesis of EG through the coal chemical industry. There are some disadvantages for the traditional methods to prepare these copper-based catalysts, for example, the active components are usually poorly dispersed for the impregnation method and the metal loading is quite low for the ion exchange method. Ammonia-evaporation method is characterized by highly dispersed active components with high metal loading, however, ammonia is very toxic. .Herein, supercritical fluid deposition (SCFD) method is proposed to synthesize Cu/SiO2 catalysts instead. Environmental benign supercritical CO2(scCO2) is used as solvent for its near zero surface tension and excellent transport property. The precursors are first dissolved in scCO2 and then brought to the nanochannels of the substrates. After physical or chemical adsorption on the substrates, the as-synthesized nano-composites are obtained after the depressurization and phase separation. There are many advantages of this method such as environmental benign, highly-dispersed active components, controllable morphology and size of the nanophase, short preparation time and so on. However, only about two decades has passed since this method was first proposed and it has not been used to prepare Copper-based catalysts for DMO hydrogenation as far as we know. .The aim of this project is to prepare highly active Cu/SiO2 catalysts with highly dispersed active components, high metal loading and high stability. Thus, the research would provide a new approach and theoretical guidance for the preparation of Copper-based catalysts. Centered around these aims, three scientific problems were focused on in this project as following:.(1) Thermodynamic phase behavior of multiple systems of inorganic salts +scCO2 + co-solvents;.(2) The basic rules and controllable parameters on controllable synthesis of Cu/SiO2 (including the size, dispersion, metal loading and the ratio of Cu+/Cu0) using SCFD method..(3) The evaluation of activity, selectivity and stability of Cu/SiO2 catalysts for the hydrogenation of dimethyl DMO to EG.

制备高效加氢催化剂是实现煤制乙二醇工业化的关键。为克服现有DMO加氢铜基催化剂制备方法的不足，如浸渍法活性组分分散性差，离子交换法担载量小，蒸氨法毒性大等，提出用超临界流体沉积法制备Cu/SiO2催化剂。以环境友好的超临界CO2为溶剂，利用其零表面张力无孔不入的传递特性，将金属前驱物溶解并输运到载体的纳米级孔道中，通过物理化学吸附作用将其沉积组装，再经减压相变实现产物和溶剂的分离。该方法具有绿色环保、纳米相高度分散、纳米相尺寸和形貌可控性好、制备时间短等优势，然而其发展历程尚短，用于该体系催化剂制备尚未见公开报道。本项目拟深入研究: ①无机盐+scCO2+共溶剂多元体系热力学相行为；②纳米相尺寸、分散度、担载量以及Cu+/Cu0比例调控的基本规律和控制参数；③催化剂用于DMO加氢制备乙二醇的活性评价；旨在为制备高分散、高担载量、高稳定的Cu/SiO2催化剂提供新的途径和理论指导。

本项目围绕高分散、高担载量、高稳定的Cu/SiO2催化剂的超临界流体法制备，设定了三个研究目标，(1)无机盐+scCO2+共溶剂多元体系热力学相行为；(2) SCFD法制备Cu/SiO2催化剂过程中纳米相尺寸、分散度、担载量以及Cu+/Cu0比例调控的基本规律和控制参数；(3) SCFD法制备的Cu/SiO2催化剂用于DMO加氢制备乙二醇的活性、选择性和稳定性评价。为了更好地实现可控制备，首先对含无机盐的高压多元体系热力学相行为进行研究，发现无机盐加入到有机溶剂+CO2体系之后，其膨胀度规律发生显著改变，加入无机盐之后，溶液会发生相分离现象，溶液浓度较高和实验温度较低有利于相分离，超临界法制备纳米复合材料过程中，应尽可能使装载体的料框位于超临界相，其位置应位于反应器的中上部。其次，为解决无机金属前驱物不溶于scCO2的问题，通过添加少量共溶剂调节其极性，促进前驱物溶解。发现在所选择的甲醇、乙醇、乙二醇、1,3丙二醇、正丁醇等共溶剂中，只有乙二醇能够使得前驱物担载到孔道内部；最后，针对乙二醇、乙二醇+水共溶剂进行研究，系统考察沉积时间、温度等对纳米形貌的调控规律。在后期深入研究过程中，发现泄压速度对纳米相影响显著，创新性提出通过精细梯度泄压控制纳米颗粒尺寸，并通过一系列表征探究所制备催化剂的催化性能。