铜助剂在铁基费托催化剂中的作用机理

Due to the rapid resource depletion, the unpredictable prices of crude oil and the drastically increased fuel demands worldwide, utilizing coal, natural gas and biomass to replace petroleum to produce chemicals and transport fuels has attracted considerable attention. One available technology is Fischer-Tropsch synthesis (FTS) which can convert synthesis gas (CO + H2) into high molecular weight hydrocarbons. Due to their low prices and high activity, iron-based catalysts are widely used in industrial FTS. To improve the stability, reactivity and selectivity of iron-based FTS catalysts, promoters or additives have been used. Experimentally Cu has been usually used as a reduction promoter. It is found that Cu can promote the reduction and carburization of iron-based catalyst, facilitate hydrogen adsorption of hydrogen, increases FTS and water-gas shift activitys. It also can affect the selectivity of FTS products, prevent deactivation of catalysts, and cooperate with other promoters. Despite of these positive effects of Cu promotor, its working mechanisms are still elusive and this hinders the development of effective and efficient FTS catalysts. However, less theoretical studies about Cu promoter are known. In order to get the the mechanistic insights of Cu promoter, we will carry out detailed density functional theory computions into roles of Cu promotor in the reduction process from Fe2O3 to Fe3O4 as well as to metallic iron and iron carbides (FeCx). We also wish to know the content effect of Cu promoter in the formation process of the stable catalysts. Furthermore we wish to know the effects of Cu promter in the elementary steps, like CO and H2 adsorption and dissociation, formation of C1 surface species (CHx) and C-C coupling reaction as well as product selectivity on iron model catalyst from the view point of atomistic thermodynamics. With the understanding into the Cu promoter mechanisms we wish to provide the possibilities for novel iron-based FTS catalysts by synthetic tuning.

能源消耗的日益严重、原油价格的波动及快速增长的燃料需求，使得费托合成技术成为人们关注的焦点。铁基催化剂因其低廉的价格和优良的催化性能被广泛应用于费托合成中，且添加助剂能提高其稳定性、活性和选择性。研究发现，Cu助剂能促进催化剂的还原与碳化，促进H2吸附，提高费托和水煤气变换反应活性，影响费托合成中的产物分布，防止催化剂失活，并能与其他金属产生协同效应。但研究者对Cu的作用机理还不是很清楚，这制约了高产高效费托合成催化剂的开发。目前有关Cu助剂的理论研究相对较少。本项目拟应用DFT理论详细研究Cu助剂对铁基催化剂还原过程的影响，Cu含量对催化剂稳定性的影响，以及Cu对铁基催化剂费托基元反应步骤如CO和H2的吸附与解离、C1表面物种(CHx)的生成、CC耦合等反应机理及产物选择性的影响，以期全面深刻理解Cu助剂的作用机理，从而使新型铁基催化剂的优化调控成为可能。

能源消耗的日益严重、原油价格的波动及快速增长的燃料需求，使得费托合成技术成为人们关注的焦点。铁基催化剂因其低廉的价格和优良的催化性能被广泛应用于费托合成中，且添加助剂能提高其稳定性、活性和选择性。研究发现，Cu 助剂能促进催化剂的还原与碳化，促进H2 吸附，提高费托和水煤气变换反应活性，影响费托合成中的产物分布，防止催化剂失活，并能与其他金属产生协同效应。但研究者对Cu 的作用机理还不是很清楚，这制约了高产高效费托合成催化剂的开发。本项目应用DFT理论详细研究Cu 助剂不同含量在铁基催化剂Fe、Fe3C、Fe5C2表面的具体存在形式，分析Cu在这些物相表面结构与稳定性差异的本质，而且研究了Cu助剂对CO吸附和解离反应、C1 表面物种(CHx)的生成反应机理的影响，理解Cu助剂抑制CO吸附与解离、抑制CH4生成的反应机理，为新型铁基催化剂的优化调控提供理论依据。另外，采用DFT计算和原子热力学方法相结合的方法，拓展研究在实际反应条件不同温度、压力下CO、H、H2O在Fe的不同表面上的覆盖度与吸附和活化机理的关系，为具有经济和生态价值的工业流程提供直接理论依据。