Abstract
Chemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape.
| Original language | English |
|---|---|
| Article number | 2630 |
| Journal | Nature Communications |
| Volume | 12 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2021 |
| Externally published | Yes |
Funding
E.G., G.M.P. and M.P. thankfully acknowledge the financial support provided by the European Union Grant No. ERC-2014-AdG-670227/VARMET. V.-A.G., R.R. and J.A.L. were supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division at Pacific Northwest National Laboratory (PNNL). E.G. was partially supported by the PNNL alternate sponsored fellowship program during a six month visit to the Richland campus. PNNL is operated by Battelle for the US Department of Energy under Contract DE-AC05-76RL01830. Computational resources were provided the Swiss National Supercomputing Centre (CSCS) under project IDs p503, s768 and s910 and the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility located at Lawrence Berkeley National Laboratory (LBNL) and operated under Contract No. DE-AC02-05CH11231.