Thermal Conductivity in Zeolites Studied by Non-equilibrium Molecular Dynamics Simulations

Abstract

The thermal conductivity of zeolites is an important material property. For example, this is the case for catalysis, where chemical reactions release heat either inside zeolites or at zeolite surfaces. At zeolite surfaces, heat is released during the adsorption of guest molecules. Unfortunately, it can be difficult to determine the thermal conductivity of zeolites from experiments or from equilibrium molecular dynamics simulations. Non-equilibrium molecular dynamics (NEMD) simulation is an interesting approach to determine thermal conductivities. Inducing a thermal gradient by moving kinetic energy between different parts of the simulation box, and then studying the resulting thermal gradient, will lead to direct access to the thermal conductivity of the zeolite. In this work, we have used NEMD simulations to determine the thermal conductivity of several pure silica zeolites. The zeolites are modeled using the Demontis force field, making it possible to screen many zeolite frameworks, and study finite-size effects. In addition, we have studied the influence of adsorbed guest molecules on the thermal conductivity. The thermal conductivity of zeolites is usually in order of 0.6 \(\mathrm{W}\cdot \mathrm{m}^{-1}\cdot \mathrm{K}^{-1}\) to almost 4 \(\mathrm{W}\cdot \mathrm{m}^{-1}\cdot \mathrm{K}^{-1}\), with large differences between different crystallographic directions. We find that the loading of guest molecules adsorbed inside the zeolite has a minor influence on the thermal conductivity, and that in general the thermal conductivity increases with increasing framework density of the zeolite.