Thermodynamic modelling of the Cu-Pd-H system

Thermodynamic modelling of hydrogen interactions with the Cu-Pd B2 alloys is used to set the stage for the development of membrane alloys with improved thermal and chemical stability for the separation of pure hydrogen from coal gasifier exhaust or syngas within advanced water gas shift membrane reactors. Thermodynamic descriptions of the binary Cu-Pd, Pd-H, Cu-H, and ternary Cu-Pd-H systems are obtained by combining experimental investigation, first-principles calculations, and thermodynamic modeling. The H solubilities in the CU0.56Pd0.44 B2 alloy have been measured from 100 to 350 degrees C up to 7 bar H-2 pressure. The stabilities of the ternary B2 phase at different compositions are predicted by first-principles calculations. The model parameters for the Gibbs energy of individual phases are optimized using experimental phase equilibrium and thermochemical data, and the first-principles predictions. The B2 phase is described with a three-sublattice model, (Cu, Pd)(0.5) (Cu, Pd)(0.5) (H, Va), which allows for ordering. The Pd-H fee miscibility gap is well described and the partial H thermodynamic quantities of the Pd-H system are in agreement with experiments. The ternary para-equilibrium and full equilibrium fcc miscibility gap are calculated for the Cu-Pd-H system. Extensive comparisons are presented between the thermodynamic modelling and experimental data. (c) 2007 Elsevier Ltd. All rights reserved.