Hydrogen interactions with the PdCu ordered B2 alloy

Abstract

Combined experimental and modeling studies on hydrogen interactions with PdCu ordered body-centered cubic (B2) alloys have set the stage for membrane alloy development for advanced water gas shift membrane reactors that separate pure hydrogen from coal gasifier exhaust or syngas. First principles potential energy surface and ground state minimization calculations were used to profile the surface site selectivity of H 2 and H 2S adsorption on the lowest energy PdCu B2 (1 1 0) surface. Finite temperature surface energy calculations for varying H 2 and H 2S coverages were used to estimate the potential for blocking of H 2 adsorption by H 2S physisorption under coal gasification partial pressure and temperature conditions. Experimental measurements of hydrogen solubility in the Pd 0.44Cu 0.56 B2 alloy were made with a Sievert's type apparatus. This data was assessed, along with existing experimental data and first principles predicted finite temperature data for hypothetical end-member phases, to develop a thermodynamic description of the ternary Pd–Cu–H system encompassing the PdCu B2 phase. First principles ground state and lattice dynamics simulations were used to predict favorable pathways for thermally activated hydrogen diffusion within the B2 lattice. The newly derived solubility and diffusivity parameters were evaluated within a mass transfer model to predict the ideal bulk permeability in the absence of other mass transfer contributions.