ABSTRACT

Water is ubiquitous in many thermal treatments and reaction conditions involving zeolite catalysts, but the potential impacts are complex. The different types of water interaction with zeolites have profound consequences in the stability, structure/composition, and reactivity of these important catalysts. This review analyzes the current knowledge about the mechanistic aspects of water adsorption and nucleation on zeolites surfaces and the concomitant role of zeolite defects, cations and extra framework species. Examples of experimental and computational studies of water interaction with zeolites of varying Si/Al ratios, topologies, and level of silanol defects are reviewed and analyzed. The different steps associated with the process of steaming, including the Al-O-Si bond hydrolysis and subsequent structural modifications, such as dealumination, mesopore formation, and amorphization, are evaluated in light of recent DFT calculations, as well as SS NMR and other spectroscopic studies. Differences between the mechanisms of water attack of the zeolite in vapor or liquid phase are highlighted and explained, as well as the effect of hydrophobic/hydrophilic properties of the zeolite walls. In parallel, the various roles of water as modifier of reactivity are reviewed and discussed, both for plain zeolites as well as rare-earth or phosphorous-modified materials.

摘要

水在许多涉及沸石催化剂的热处理和反应条件中无处不在，但潜在的影响是复杂的。不同类型的水与沸石的相互作用对这些重要催化剂的稳定性、结构/组成和反应性具有深远的影响。这篇综述分析了目前关于沸石表面吸水和成核的机理方面的知识，以及沸石缺陷、阳离子和额外骨架物质的伴随作用。回顾和分析了水与不同 Si/Al 比率、拓扑和硅烷醇缺陷水平的沸石相互作用的实验和计算研究的例子。与汽蒸过程相关的不同步骤，包括 Al-O-Si 键水解和随后的结构修改，例如脱铝，根据最近的 DFT 计算以及 SS NMR 和其他光谱研究来评估中孔形成和非晶化。强调并解释了沸石在汽相或液相中的水侵蚀机制之间的差异，以及沸石壁的疏水/亲水特性的影响。同时，回顾和讨论了水作为反应性改性剂的各种作用，包括普通沸石以及稀土或磷改性材料。以及沸石壁的疏水/亲水特性的影响。同时，回顾和讨论了水作为反应性改性剂的各种作用，包括普通沸石以及稀土或磷改性材料。以及沸石壁的疏水/亲水特性的影响。同时，回顾和讨论了水作为反应性改性剂的各种作用，包括普通沸石以及稀土或磷改性材料。