CRC 1109/1: Hydration and Hydrolysis in Dealumination and Desilication of Zeolite Frameworks (SP D04)

In spite of a large and increasing number of experimental and computational studies, atomistic understanding of the hydrothermal synthesis of zeolites has not yet been achieved. Previous work has shown that a divide-and-conquer strategy may be very helpful in which complexity is reduced and sub-problems are studied. Here, we address the interaction of microporous alu-mosilicate frameworks with water with respect to de/re-alumination and de/re-silication of framework structures, which are crucial reactions in the post-synthesis processing of zeolites. We study the thermodynamics and kinetics of elementary steps of the latter reactions using advanced techniques for the computations of the potential energy surfaces. In particular, we examine the interaction of an increasing number of water molecules with hydrophilic bridging hydroxyl sites, SiO(H)Al(OSi)3, and the hydrophobic silica surface SiOSi(OSi)3. Central ques-tion is the role of molecular adsorption of water, forming, e.g., (H2O)4H+ species on bridging hydroxyl sites, as compared to the hydrolysis of Al-O-Si bonds resulting in extra-framework-Al-species and hydroxyl nests [(-O)3SiOH]4, also known as hydrogarnet defects. We are interest-ed in the effect of different framework structures and the crystallographic position within a giv-en framework, including the recently prepared new two-dimensional zeolite film.