【作者】 徐悦；

【导师】 袁渭康； 李平； 朱贻安；

【作者基本信息】 华东理工大学 ， 化学工程， 2014， 博士

【摘要】 非均相催化反应发生在微观空间和瞬态时间尺度上,如何获得反应精确信息,掌握并调控反应机理,从而指导催化剂设计,一直是传统实验研究面临的难题。计算催化理论的建立和发展,尤其是密度泛函理论(DFT)的提出,使得捕捉催化剂表面反应过渡态,了解反应瞬间催化体系的能量变化,理清反应路径和决速步骤,最终实现催化剂的理性设计成为可能。本文以基于DFT的计算方法为手段,以甲烷水蒸汽重整和甲烷二氧化碳重整为两个模型反应,系统地研究了金属催化剂表面上的微观反应动力学,开发出了为非均相催化反应筛选金属及合金催化剂的通用计算方法。本文主要研究内容及结果如下：(1)基于金属Ni为催化剂,研究了甲烷解离对于Ni不同表面的结构敏感性。计算并对比了甲烷解离中间产物在平板面Ni(111)和台阶面Ni(211)上的吸附能,以及相关基元反应的活化能；以Ag为表面合金组分,研究了Ag部分覆盖对Ni表面性质和催化作用的影响。计算了Ag单层覆盖率为1/9及1/4时甲烷解离中间产物的吸附能和相关基元反应的活化能,比较了C-C结合和C-O结合两个基元反应的活化能,讨论了添加Ag对甲烷解离导致Ni表面结焦的影响。(2)研究了不同金属表面上,甲烷重整反应体系吸附质的吸附能与碳和氧吸附能之间存在的尺度关系,以及过渡态能量与产物能量之间的尺度关系,并将这些尺度关系加入后续微观反应动力学模型中,建立了以碳和氧的吸附能为两个描述符的二维火山形反应速率图。(3)研究了吸附质与吸附质之间的相互作用,计算了几种金属(211)表面上,甲烷重整反应体系吸附质在不同吸附位之间的相互作用,及其对吸附能的影响。通过计算吸附质在不同吸附位不同覆盖率下的吸附能,回归参数至分段吸附质相互作用模型中。将吸附质相互作用模型加入微观反应动力学研究,计算了甲烷水蒸汽重整和二氧化碳重整体系中各个吸附质的微分吸附能,得到了合理的中间产物覆盖率。(4)建立了以碳、氧吸附能为两个描述符的,基于拟定态假设的微观反应动力学模型,在模型中包含了吸附质与吸附质之间的相互作用,计算了甲烷水蒸汽重整和二氧化碳重整在不同反应条件下的反应速率。(5)由甲烷水蒸汽重整和二氧化碳重整的微观反应动力学模型得到的火山形曲线速率图,根据碳、氧吸附能两个描述符,筛选了600多种体相合金催化剂。结合合金催化剂在实际反应条件下的稳定性与当前催化剂材料价格,最后得到了多种同时具有高活性、高选择性、高稳定性且廉价的合金催化剂,其中Ni3Fe和Co3Ni都能用于上述两个重整反应。更多还原

【Abstract】 The development of catalysis is of fatal importance to modern and future society. It is the foundation of modern chemical industry. Raw materials such as petroleum and natural gas can be readily converted to chemicals by catalysis, supplying daily needs of transportation, food production and medical treatment for the community. Nowadays, the development of catalytic science has become the main power for the improvement of commercialized chemical processes, and it will be, in the future, the base stone of changing energy infrastructure, utilizing sustainable energy sources such as solar, wind and biomass. Some existing technology problems are also closely related to the catalysis science, e.g., energy saving and consumption reduction requirement of hydrogen production in the hydrocarbon steam reforming process for ammonia synthesis; Ni-based catalyst deactivation in the methane dry reforming process for high CO/H2synthesis gas production as the feedstock for further Fisher-Tropsh synthesis. However, due to the complexity of catalytic reaction process, the development of active, selective and stable catalysts still faces many scientific challenges.In order to design catalysts rationally, the fundamental understanding of interactions between adsorbates, catalyst surfaces, and the transition states of the elementary reactions are essential. Recent advances in computational chemistry, particularly density functional theory (DFT) made it possible to investigate reactions "in silicd". In this paper, a method based on DFT for screening for active, selective, stable and inexpensive catalyst for a large range of heterogeneous catalyst is presented. Steam and dry reforming of methane reactions were used as two model reactions to demonstrate this method.The main content of this thesis is as follows:(1) Using Ni catalyst as an example, surface structure sensitivity for methane decomposition was investigated on close packed Ni(111) and stepped Ni(211) facets. The adsorption energies of related adsorbates, the activation energies for all the elementary reactions of methane decomposition were calculated. In order to study the effect of second metal on the catalytic properties of the surface alloy, Ni(111)and Ni(211) surfaces with different silver coverages (1/4monolayer,1/9monolayer) were constructed. The energetics of the intermediates for methane steam reforming were calculated and compared with the ones on pure Ni surfaces. Coking mechanism wasinvestigated by comparing the activation barrier for C-0and C-C on Ni and Ag/Ni systems. Equilibrium shape of the catalyst crystalline was estimated by employing Wulff construction. Proportion of each surface was estimated and the effect of introduced silver was discussed.(2) Scaling relations between adsorption energies of the adsorbates and the adsorption energies of carbon and oxygen were investigated. Scaling relations between transition state energies and final state energies were also studied in both methane steam and dry reforming systems. Then the scaling relations were incorporated to a microkinetic model, which results in a two descriptor based volcano shaped rate plot. The volcano plot was further used as the check board for screening for active and selective alloy catalysts.(3) Adsorbate-adsorbate interactions were investigated on stepped (211) surfaces premise to mean field theory. Cross interaction parameters between different adsorbates and different adsorption sites were parameterized in a piecewise adsorbate-adsorbate interaction model. The adsorbate-adsorbate model was further incorporated in a microkinetic model to calculate differential adsorption energies to obtain reasonable coverages for the steam and dry methane reforming systems.(4) Descriptor-based volcano rate plots for methane steam and dry reforming were constructed that combines a microkinetic model with scaling relations while taking adsorbate-adsorbate interactions into consideration.(5) Using rates obtained by the comprehensive microkinetic model for different reaction conditions, screen thousands of transition metal and alloys by using carbon and oxygen as the two descriptors. Combing filters that consider stability and cost enables the screening for novel leads for active, stable, and inexpensive alloy catalysts.更多还原