金属离子改性ZSM-5上HCN催化水解的理论与实验研究

Recently, as one of the most promising methods for the purification of emissions containing HCN, the catalyzed hydrolysis of HCN has received widespread attention. But the toxic HCN leads to the danger and complexity of experiments, which restricts the deep understanding of the reaction mechanism. Based on the experimental research, the project intends to use quantum chemistry to explore the adsorption of HCN and H2O on Cu-ZSM-5 and Fe-ZSM-5 zeolites, and the reaction mechanism of HCN hydrolysis catalyzed by Cu-ZSM-5 and Fe-ZSM-5. We will investigate all possible reaction channels and confirm the intermediates and transition states by frequency analysis and intrinsic reaction coordinate (IRC), obtain kinetic information, the charge distribution and the nature of orbits. And we will reveal the connections between the alkaline properties and the catalytic hydrolysis of HCN by introducing alkali and alkaline earth metals to build basic sites. Moreover, the features of the other transition metal-ion modified ZSM-5, such as the type, the density of states, the energy band structure, the orbit nature, the electronic structure and the coordination environment of metal ion, and the internal relations between the catalyzed reactions with the features will be studied, to derive the key catalyzing step and to analysis microscopic reaction mechanism. Finally, auxiliary experiments will be carried out to verify the reliability of theoretical calculations. The project will provide theoretical and technical support for HCN air pollution control.

催化水解法作为净化工业废气中HCN最有前景的方法之一近年来受到广泛关注。但HCN的剧毒性导致了实验的危险性和复杂性，也制约了对该反应机理的深入认识。本项目拟结合实验研究结果，采用量子化学方法探索Cu-ZSM-5和Fe-ZSM-5分子筛对HCN和H2O的吸附活化及HCN催化水解反应机理；考察所有可能的反应通道；通过频率分析和内禀反应坐标(IRC)计算确认过渡态和中间体；获得动力学信息、电荷分布和轨道性质等；引入碱（土）金属构筑碱性位揭示催化剂的碱性质与HCN催化水解间的联系规律。此外，研究其他过渡金属离子改性ZSM-5分子筛的种类、态密度、波带结构、轨道性质，活性金属的电子结构和配位环境与HCN和H2O的吸附活化及HCN催化水解的内在联系规律，得出HCN催化水解的化学原理和催化关键，并解析微观动力学过程。最后，通过辅助实验验证理论计算的可靠性。本项目将为HCN废气污染控制提供理论和技术支撑。

本项目首先研究了无催化剂下HCN及其类似物（乙腈和丙烯腈）的水解反应机理，设计了HCN与H2O反应的三条途径，并考虑了在计算模型中添加一个H2O分子协助HCN水解。然后采用量子化学理论计算方法探索了Cu-ZSM-5分子筛对HCN和H2O的吸附活化及HCN催化水解反应机理。对于在Cu-ZSM5催化剂上HCN的水解反应，共设计了五种可能的反应路径（路径I，II，III，IV和V），通过频率分析和内禀反应坐标(IRC)计算确认过渡态和中间体。研究发现HCN催化水解反应的催化关键是质子转移，且HCN中C原子上连接的H原子转移到N上是速度控制步骤。因此进一步采用密度泛函方法研究了Cu-ZSM5上HCN催化水解过程中的各种质子转移方式。研究发现当在反应中形成双向质子转移往往能降低活化自由能垒，同时质子转移周围的原子环境也会影响反应的自由能垒。这为后续进一步探索质子转移最优方式奠定了基础。最后本项目制备了一系列在不同温度下煅烧的Fe-Ti-Ox催化剂并用于HCN的催化水解反应。