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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)

- Scott M. Auerbach, Fabien Jousse, Daniel P. Vercauteren
- 2002

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)

- Harikrishnan Ramananand, Scott M. Auerbach
- 2004

We review the macroscopic variables relevant to single-component mass transfer through fixed zeolite particles or membranes. Through the Fick and Maxwell-Stefan formulations of diffusion, we relate these variables to transport coefficients calculable with molecular simulations. Using the Fick formulation, we discuss the diffusion-controlled and… (More)

- Vishal Agarwal, George W. Huber, Curtis Conner, Scott M. Auerbach
- 2009

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)

Nanoporous acid catalysts such as zeolites form the backbone of catalytic technologies for refining petroleum. With the promise of a biomass economy, new catalyst systems will have to be discovered, making shape-selective base catalysts especially important because of the high oxygen content in biomass-derived feedstocks. Strongly basic zeolites are… (More)

- R. Astala, Scott M. Auerbach, P. A. Monson
- 2004

We have investigated various silica zeolites using density functional theory with periodic supercells, plane waves, and pseudopotentials. These zeolitic phases include silica sodalite, chabazite, mordenite, silica LTA, and silicalite. Atom-level geometries, elastic properties, and cohesive energies are presented. Although the zeolites exhibit a wide range… (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)

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)

- Scott M. Auerbach, tJl, Neil J. HensontJI, Anthony K. CheethamJf, ll
- 2001

We have modeled benzene diffusion in Na-Y zeolite (%:A1 = 2.0) over the temperature range 100-500 K. We apply the kinetic Monte Carlo random walk model, with activation energies derived from a new zeolite-hydrocarbon potential energy surface (PES). An Arrhenius fit yields the apparent activation energy E, = 41 kJ mol-', as compared with the previously… (More)