Learn More
We have studied the convergence properties of embedded and constrained cluster models of proton transfer in zeolites. We applied density functional theory to describe clusters and ONIOM to perform the embedding. We focused on converging the reaction energy and barrier of the O(1) to O(4) jump in H-Y zeolite as well as vibrational and structural aspects of(More)
We review theory and simulation of rare event dynamics, diffusion and phase equilibrium in nanopores, focusing on benzene in Na-X and Na-Y zeolites because of persistent experimental discrepancies. We discuss transition state theory and its application to zeolite–guest systems, suggesting that calculations on flexible lattices and at finite guest loadings(More)
We present Monte Carlo simulations of a lattice model describing silica polymerization with an emphasis on the transition between gel states and nanoparticle states as the pH and silica concentration are varied. The pH in the system is controlled by the addition of a structure-directing agent (SDA) of the type SDA(+)(OH(-)). The silica units are represented(More)
We have constructed and applied an algorithm to simulate the behavior of zeolite frameworks during liquid adsorption. We applied this approach to compute the adsorption isotherms of furfural-water and hydroxymethyl furfural (HMF)-water mixtures adsorbing in silicalite zeolite at 300 K for comparison with experimental data. We modeled these adsorption(More)
We explore recent efforts to model the dynamics of sorbed molecules in zeolites with either atomistic methods or lattice models. We discuss the assumptions underlying modern atomistic and lattice approaches, and detail the techniques and applications of modeling both rapid dynamics and activated diffusion. We summarize the major findings discovered over the(More)
We have modeled structures and energetics of anhydrous proton-conducting wires: tethered hydrogen-bonded chains of the form ···HX···HX···HX···, with functional groups HX = imidazole, triazole, and formamidine; formic, sulfonic, and phosphonic acids. We have applied density functional theory (DFT) to model proton wires up to 19 units long, where each proton(More)
We have modeled permeation through anisotropic zeolite membranes with nanoscopic defects that create shortcuts perpendicular to the transmembrane direction (x). We have found that the dimensionless ratio D y /(k d y) can be used to estimate whether the shortcuts contribute significantly to the overall flux. Here D y is the diffusion coefficient for motion(More)
We present an efficient Monte Carlo algorithm for simulating diffusion in tight-fitting host–guest systems, based on using zeolite normal modes. Computational efficiency is gained by sampling framework distortions using normal-mode coordinates, and by exploiting the fact that zeolite distortion energies are well approximated by harmonic estimates.(More)
Keywords: Nitrided zeolites Solid base catalysts Ammonolysis Mechanism Nudged elastic band ONIOM Density-functional theory a b s t r a c t We have performed embedded-cluster calculations using density functional theory to investigate mechanisms of nitrogen substitution (nitridation) in HY and silicalite zeolites. We consider nitridation as replacing Si–O–Si(More)