Understanding Thermal Transport in Porous Crystals

Highly porous materials are very useful for chemical separations, catalysis, and gas storage. The last twenty years has been particularly exciting in this area because of the discovery of highly porous crystals called metal-organic frameworks (MOFs). By changing the building blocks used in their self-assembly, their pore structures can be tuned to target specific applications, and in two decades over 70,000 different MOFs have been reported in the literature.
However, an important property for the practical implementation of MOFs as industrial adsorbents has received relatively little attention over that time: thermal transport. Whenever gases are rapidly loaded and unloaded in porous materials, there is a sharp increase and decrease of temperature. In just the last few years, our understanding of thermal transport in porous crystals, and MOFs in particular, has increased significantly. Through molecular simulations, we have investigated the thermal conductivity of MOFs both as a function of their pore structure and also as function of gas loading [1-2]. An important observation of ours, which is contested and for which experimental support is scarce, is that thermal conductivity of MOFs generally decreases in the presence of adsorbed gases [3]. This observation, if found to be hold as a general phenomenon, implies greater challenges for MOFs as gas adsorbents: not only are they typically insulating materials to begin with, but their insulating nature is exacerbated by the presence of gases. In this talk we present our collected evidence on this important phenomenon and outline potential strategies to control and mitigate unwanted thermal effects in gas adsorption scenarios.