Computational Efforts in Support of Advanced Coal Research

Abstract

The focus in this project was to employ first principles computational methods to study the underlying molecular elementary processes that govern hydrogen diffusion through Pd membranes as well as the elementary processes that govern the CO- and S-poisoning of these membranes. Our computational methodology integrated a multiscale hierarchical modeling approach, wherein a molecular understanding of the interactions between various species is gained from ab-initio quantum chemical Density Functional Theory (DFT) calculations, while a mesoscopic statistical mechanical model like Kinetic Monte Carlo is employed to predict the key macroscopic membrane properties such as permeability. The key developments are: (1) We have coupled systematically the ab initio calculations with Kinetic Monte Carlo (KMC) simulations to model hydrogen diffusion through the Pd based-membranes. The predicted tracer diffusivity of hydrogen atoms through the bulk of Pd lattice from KMC simulations are in excellent agreement with experiments. (2) The KMC simulations of dissociative adsorption of H{sub 2} over Pd(111) surface indicates that for thin membranes (less than 10{micro} thick), the diffusion of hydrogen from surface to the first subsurface layer is rate limiting. (3) Sulfur poisons the Pd surface by altering the electronic structure of the Pd atoms in the vicinity of the S atom.more » The KMC simulations indicate that increasing sulfur coverage drastically reduces the hydrogen coverage on the Pd surface and hence the driving force for diffusion through the membrane.« less