Formation, structure and dynamics of hydroxyl nest defects in zeolites.

Hydroxyl nest defects in zeolite frameworks, formed through the removal of T-sites followed by hydrolysis, are of critical importance for catalytic applications due to their high reactivity and role in stabilizing metal species. This study employs hybrid QM/MM calculations to characterize single hydroxyl nests in several zeolite frameworks, focusing on formation energies and structures and on the atomic-level mechanisms governing proton dynamics. In particular, we distinguish between proton rotation around oxygen atoms and proton transfer between different hydroxyl sites. Using Nudged Elastic Band (NEB) calculations, we determine the energy barriers for both mechanisms in chabazite. Our results reveal a negative (favourable) formation energy for these defects in ZSM-5, faujasite and quartz (in chabazite it is close to zero) and show that the framework geometry significantly affects the energetics of proton mobility, with rotation often favoured in constrained environments. Structural data and bond angle analysis are reported for each framework. These findings contribute to the understanding of proton behavior in defective zeolites and offer insights for tailoring catalytic properties through defect engineering.