The effect of Si/Al ratio on local and nanoscale water diffusion in H-ZSM-5: A quasielastic neutron scattering and molecular dynamics simulation study

The dynamics of water confined in H-ZSM-5 (protonated form the Zeolite Socony Mobil – 5) has been studied using quasielastic neutron scattering (QENS) and classical molecular simulations (MD). QENS measurements probed ZSM-5 samples with Si/Al ratios 15, 40 140 at 2.8 wt% loadings. In lower silica samples, fitting elastic incoherent structure factor (EISF) showed that diffusion was to a sphere (with radii ranging from 3.4 4.3 Å), suggesting mobile located within MFI (framework type H-ZSM-5) channel intersections, giving localised coefficients range ∼0.9–1.8 × 10−9 m2s−1. high zeolite, observed be far less more long nature, significantly higher than systems (∼1.8–4.8 m2s−1). MD further investigated effect ratio on diffusivity loading (9 molecules/unit cell (UC)) = 47, 95 fully siliceous. had significant calculated nanoscale water, reducing self-diffusion coefficient by 2 siliceous system due strong coordination increased residence time molecules Brønsted acid sites which ∼5 ps ∼2 15 respectively. observables, both EISF line broadenings, were reproduced trajectories upon sampling experimental timescale qualitative quantitative agreement experiments. Fitting experimentally 3.5 6.8 Å also present our simulations, 0.5 experiment.