Rh和Pt团簇催化净化汽车尾气反应机理的理论研究

Catalytic conversion of automobile exhaust, such as the reduction of NOx and hydrocarbon cracking, is a major challenge in environment and catalysis research because of the green house effect of these gases. Rh-based and Pt-based catalysts are the components responsible for the removal of NO and the cracking of hydrocarbons,respectively. The density functional theory, quantum mechanics, molecular mechanics, molecular dynamic simulation, and surface kinetic simulation methods are explored to investigate the above catalytic reaction mechanisms. The contents of the present investigation are as follows: (a) to design RhnMm and PtnMm (M = Ni and La et al)clusters, (b) to provide insight into the intrinsic property and catalytical efficiency of the purification of automobile exhaust on RhnMm and PtnMm cluster, (c) to explore the effect of temperature and pressure on the reactivity and selectivity of dynamic purification of automobile exhaust, (d) to accumulate the thermodynamic and kinetic data, e.g. rate constant and branching ratio of products under different temperature and pressure, and the difference of Gibbs free energy, (e) to acquire the determining transition state and intermediate of catalytic turnover frequency, and (f) to elucidate the effect of nonnoble-metal promoter on the structure and property of Rh-based and Pt-based catalysts. The the present investigation is helpful to the understand the nature of catalytic reactions, and design and develop effective, cheap, and practical catalysts for the removal of automobile exhaust. It is very important to explore the rule of the complicated system kinetics, to control and remove envirnomeantal pollution, and innovate the low-carbon technology.

以减少和消除汽车尾气污染为背景，降低尾气净化催化剂中贵金属用量为目标，采用密度泛函理论、量子力场和分子力场相结合、分子动力学模拟、表面动力学模拟等方法，以NO还原和烷烃裂解为模型反应，设计适宜的RhnMm和PtnMm (M = Ni和La 等)团簇模型，研究催化剂活性组分团簇对NO还原和烷烃裂解催化反应的影响，探求温度和压力对其动态催化反应活性和选择性影响的实质，阐明催化反应机理，获取决定催化效率的关键过渡态和中间体，积累NO还原和烷烃裂解催化反应的热力学和动力学参数（如反应速率常数和产物选择性等），明确非贵金属助剂对Rh和Pt团簇模型催化剂结构和性能的影响。为设计合成降低Rh和Pt用量的新型高效廉价的汽车尾气净化催化剂提供理论依据。对探索复杂体系动力学规律、控制和治理环境污染、创新低碳技术具有重要意义。

氮氧化合物的催化还原和烷烃的催化裂解对控制和治理环境污染具有重要意义。本项目采用量子化学计算的方法，将非贵金属助剂引入到Rh团簇和Pt团簇建立模型催化剂，研究在其模型催化剂上NO还原和低碳烷烃裂解的催化反应机理。分别研究了以下催化反应机理：(1)、设计优化了催化剂团簇模型RhnPdm (n + m = 4)，获得了在Rh4、 Rh4+、Rh2Pd2等团簇模型上NO 还原（NO + CO → N2 + CO2）的催化反应机理。结果表明，CO促进了NO中N-O键的断裂，Pd的参与有利于CO2的生成；(2)、设计优化了Pt2、Pt6和PtnNim (n+m = 4)以及Pt/γ-Al2O3等催化剂模型，获得了在Pt2、Pt6和PtnNim (n+m = 4)以及Pt/γ-Al2O3等模型催化剂上C2H6或C3H8的催化裂解机理。结果表明，催化剂活性组分Pt具有很高的C-H键活化能力，同时具有较强的吸附H2和C2H4的能力，使得其释放H2和C2H4的能力很差，从而降低了催化活性。而非贵金属助剂Ni和载体γ-Al2O3分别与Pt发生协同作用，使得释放H2和C2H4更加容易，从而提高了催化活性。(3)、获得了M原子、MO分子和MO+正离子（M = Fe和Ni）等催化乙炔三聚环化生成苯（3C2H2 → C6H6）的反应机理。结果表明，MO分子具有最高的催化活性。理论计算所得到的相关物种的红外振动频率数据可为实验研究中相关新物种的光谱认证提供有力帮助。该项目成果可为设计合成降低Rh和Pt用量的新型高效廉价的汽车尾气净化催化剂提供理论依据，对探索复杂体系动力学规律具有重要意义。