基于甲醇直接氧化酯化的纳米金催化剂的制备及反应性能研究

Compared with the traditional methods, methanol selective oxidation to methyl formate at low temperature is considered as simple, high efficiency and green chemistry and so on. The main challenge is to look for effective catalysts. In term of the advantage of nano-gold catalyst at the low temperature selective oxidation, this project is to explore an efficient gold catalyst system for the methanol oxidation to methyl formate. Firstly a series of gold-based catalysts with different Au sizes or shapes and supports are controllable synthesized through tuning the preparation methods and the preparation parameters. Then the catalytic performance for the selective oxidation of methanol is carried out. The influences of the preparation methods, the nature of supports, the size/shape of gold particles and the incorporation of a second metal promoter on the catalytic performance are investigated. The relationship between the catalytic structure and catalytic performance will be also studied. Based on these results, a new effective nano gold based catalyst for the selective oxidation of methanol to methyl formate will be designed and prepared. Finally, the reaction mechanism including the adsorption/desorption of reactants, products and reaction mediates will be studied by experimental as well as theoretical methods. This work will provide the experimental and theoretical foundation for the further research on the selective oxidation of methanol to methyl formate over gold based catalysts.

甲醇低温选择氧化制高附加值的甲酸甲酯过程较传统的生产方法具有工艺过程简单、能耗低、效率高、绿色环保等优点，其核心问题是寻找有效的催化剂。本项目针对甲醇直接氧化酯化反应，拟利用纳米金催化剂在低温选择氧化反应方面的优势，通过对催化剂制备技术的改进及制备参数的调变来实现纳米金催化剂颗粒尺寸和形貌结构的精确控制，研究催化剂载体选择、金粒尺寸和形貌结构以及引入其它金属等因素对甲醇选择氧化制甲酸甲酯催化性能的影响，探讨催化剂结构与性能之间的关系，为甲醇氧化制甲酸甲酯探索出一种新型、高效的纳米金催化剂体系。同时，对反应物、产物和反应中间体的吸脱附行为及其转化机理进行原位、动态的表征，并与理论计算相结合，探明金催化剂上甲醇选择氧化制甲酸甲酯的反应机理，为纳米金催化甲醇直接选择氧化制甲酸甲酯的进一步研究与开发提供实验及理论依据。

甲醇选择氧化是制备甲醇下游产品的一条重要途径。甲醇直接氧化生成甲酸甲酯在热力学上是可行的，其核心问题是高效催化剂的开发。本项目借助于纳米金催化在低温选择氧化方面的优势，通过对催化剂制备技术的改进和拓展及制备参数的优化实现了对金催化剂形貌、颗粒尺寸以及晶相结构等的可控合成，探索了催化剂结构和催化性能的构效关系。首先以SiO2为载体，采用溶胶固定法制备了Au/SiO2催化剂，研究了Au/SiO2上甲醇直接氧化酯化的催化反应性能，发现100 oC时，甲醇既可以发生氧化，在150 oC时甲醇的转化率为29.2%，甲酸甲酯的选择性为100%。然后通过引入其它金属（Pd，Cu和Ag）与金协同来进一步提高催化剂的反应性能，利用溶胶固定法制备了Au-Pd/SiO2，Au-Cu/SiO2，Au-Ag/SiO2催化剂，考察了这三种催化剂上的甲醇氧化反应性能，发现这三种催化剂的起燃温度有所不同，分别是20， 120 和140 oC，显然Au-Pd/SiO2对甲醇氧化有较高的催化活性，在90 oC时甲酸甲酯选择性为100%，且反应温度窗口较宽。随后我们对Au和Pd的相对组分含量进行了优化，发现金钯质量比为2：1时，催化性能最佳。其次采用石墨烯作为载体，制备了Au2.0-Pd1.0/Graphene催化剂，在70 oC 时甲醇转化率达到90.2%，甲酸甲酯选择性为100%，同时该催化剂具有较好的稳定性。同时，以碳纳米管和石墨烯复合材料作为载体，制备了Au-Pd催化剂，发现碳纳米管作为支撑物和石墨烯形成了三维多孔结构，不仅可以有效避免石墨烯在成型过程中的堆叠，还可以促进金钯合金的生成，可控合成小粒径的金属颗粒，有助于催化性能的进一步提高。