Dissociation, Dissolution, and Diffusion of Nitrogen on VxFey and VxCry Alloy Membranes Studied by First Principles

Abstract

N2-selective metal membranes could be used to couple extraction of N2 from flue gas and NH3 synthesis within a single membrane reactor. The larger interstitial spaces of BCC metals makes them attractive for fast permeation of the large N atom. The caveat is that N permeabilities reported thus far for pure BCC metals (e.g. V, Cr, Fe, Mo, W) are insufficient for practical application. However, practical permeabilities could be achieved by alloying these metals. Here, we use density functional theory (DFT) to study how alloying V—a metal with high N solubility but low N diffusivity—with Fe and Cr impacts the dissociation, dissolution and diffusion of nitrogen. Although N binding at vacancies was studied, binding at these defects was not particularly strong compared to regular interstitial sites, and, thus, may not significantly affect solubility. The alloys present two types of interstitial octahedral (o) sites: V-rich (o1) and V-depleted (o2). Nitrogen binding strength correlates with number of V nearest-ne...