铂基催化剂丙烷脱氢反应中积碳生成机理的计算化学研究

Coke formation is one of the key factors which leads to catalyst deactivation. The research of coke formation mechanism over catalyst surfaces could help to improve current industry catalysts, as well as design new types of catalysts. Traditionally, experimental based researches are hard to identify the structure of active sites as well as the catalytic reaction mechanism at molecular level. In this project, we will study the dehydrogenation and coke formation activity over different types of catalytic sites (e.g., Pure Pt, Pt alloy and support etc.), by employing a model reaction: propene formation from propane dehydrogenation. A multidimensional calculation plan will be applied at three different levels: molecular level; micro level; mathematic model. In order to build a reasonable catalyst model, the global minimum of alloy and alloy / support interface will be optimized with genetic algorithm. Afterwards, the thermodynamic and kinetic information of elementary steps on the optimized model catalysts will be calculated using density functional theory, and a micro-kinetic model will be built to analyze the selectivity of various products and identify the rate-determining step. We will come up with a mathematical model by adopting the scaling relationship based on the dominant reaction mechanism. All these information obtained at different theory levels will help to uncover the general rules of coke formation, dehydrogenation selectivity and activity over Pt based catalysts. The successful execution of this project will provide deep understanding of dehydrogenation and coke formation mechanisms and offer new theoretical guideline and foundation for catalyst design and improvement.

积碳是导致催化剂失活的重要因素之一。通过研究积碳在催化剂表面的生成机理，能够从理论上指导现有工业催化剂的改良及新型抗积碳催化剂的设计。传统的以实验为基础的研究方法，难以在分子层面上确定活性位点的结构，解释相应的催化反应机理。本课题采取“分子尺度－微观尺度－数学模型”的跨尺度模拟研究方案，以丙烷脱氢制乙烯为模型反应，研究铂合金、助催化剂及载体对脱氢活性和积碳生成的影响。通过遗传算法确定合金催化剂及掺杂氧化物载体的最稳定结构，建立合理催化剂模型。通过密度泛函理论及微观动力学模拟，得到不同反应条件下产物的选择性，确定反应机理及速控步。结合吸附能－活化能等线性比例关系建立相应的动力学数学模型，实现该类催化剂催化效果的快速预测。通过综合分析不同体系的研究结果，提出影响铂基催化剂活性、选择性的一般规律。本项研究能够加深人们对脱氢反应及积碳生成的了解，为脱氢催化剂的快速设计和优化提出理论指导依据。

Pt基催化剂具有较高的活化C-H键的能力，但是由于其断C-C键的能力较强。使得其在催化丙烷脱氢的过程中会产生甲烷、乙烷、积碳等副产物。因此合成具有优良活性和选择性的丙烷脱氢催化剂是人们研究的热点。本课题组使用计算化学的方法指导改性Pt基催化剂的合成。通过引入第二种金属形成合金的方式来调节Pt的电子结构以提高Pt系催化剂的丙烯选择性。我们也发现Pt单原子合金能够打破脱氢过程中限制铂基二元合金催化性能的线性关系，在保持本征脱氢活性的同时，极大提高产物丙烯的选择性。此外，由于Pt的价格高昂。为了减少Pt的用量，我们也设计合成了氧化锌和氧化钒催化剂。深入研究了其构效关系，指导催化剂的合理设计。