Transition state theoretical modelling of molecular diffusion within the narrow pores of brewsterite zeolite

Context

Based on the transition state theory, a molecular diffusion model in the narrow channels of Brewsterite zeolite was established. In this model, the molecular interaction at the potential barrier was simplified to only consider the repulsive potential, so that the analytical relationship between the diffusion coefficient and the temperature and the Lennard–Jones interaction parameter was derived. We used the molecular dynamics method to simulate the diffusion of four molecules, CF₄, CH₄, Ar, and Ne, in Brewsterite zeolite and evaluated the rationality of the model. The results show that the three molecules CF₄, CH₄, and Ar meet the predictions of the model, while the Ne molecule does not. At the same time, by analyzing the trend of the diffusion coefficient with the load, we further explain the reason for this difference. In short, this study reveals the diffusion mechanism of molecules in the narrow pores of Brewsterite zeolite. This provides new ideas for optimizing the performance of zeolite materials and applying them to catalysis and separation processes.

Methods

The simulations were carried out with Refson’s MOLDY code in the NVT ensemble. The short-range Lennard–Jones forces were calculated with the link cell method. A Nose–Hoover thermostat was used to realize the thermal equilibrium state of the samples. In the simulation, the time steps were 1 fs and the total simulation time was 51 ns. The initial temperature was set to 300 K.