Journal of Alloys and Compounds 446–447 (2007) 583–587
Hydrogen interactions with the PdCu ordered B2 alloy
S.M. Opalka
a,∗
, W. Huang
b
, D. Wang
c
, T.B. Flanagan
c
, O.M. Løvvik
d,e
,
S.C. Emerson
a
, Y. She
a
, T.H. Vanderspurt
a
a
United Technologies Research Center, 411 Silver Lane, East Hartford, CT 06108, United States
b
QuesTek Innovations LLC, 1820 Ridge Avenue, Evanston, IL 60201, United States
c
Department of Chemistry, University of Vermont, Burlington, VT 05405, United States
d
University of Oslo, Centre for Materials Science and Nanotechnology, P.O.B. 1126 Blindern, NO-0318 Oslo, Norway
e
Institute for Energy Technology, P.O.B. 40, NO-2027 Kjeller, Norway
Received 24 October 2006; received in revised form 19 January 2007; accepted 22 January 2007
Available online 30 January 2007
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
2
S adsorption on the lowest energy PdCu B2 (1 1 0) surface. Finite temperature surface energy calculations for varying H
2
and H
2
S coverages
were used to estimate the potential for blocking of H
2
adsorption by H
2
S physisorption under coal gasification partial pressure and temperature
conditions. Experimental measurements of hydrogen solubility in the Pd
0.44
Cu
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.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Metals and alloys; Hydrogen adsorbing materials; Phonons; Diffusion; Thermodynamic modeling
1. Introduction
Advanced water gas shift membrane reactors (AWGSMR)
use hydrogen-selective membranes to increase the conver-
sion of coal or natural gas-derived syngas to H
2
by the
heterogeneously catalyzed water gas shift (WGS) reaction,
CO + H
2
O ⇆ CO
2
+H
2
(H
reaction
= -41 kJ/mol). The exother-
mic WGS reaction is kinetically controlled at low temperatures
and thermodynamic equilibrium-controlled at high tempera-
tures. The use of a membrane to continuously remove the H
2
product increases the conversion rate at high temperatures, shift-
ing the reaction towards completion. The AWGSMR path to low
cost H
2
production eliminates the need for multi-stage WGS
∗
Corresponding author. Tel.: +1 860 610 7195; fax: +1 860 610 1661.
E-mail address: opalkasm@utrc.utc.com (S.M. Opalka).
reactors with intermediate cooling, carbon oxide cleanup units,
and pressure swing adsorption units, resulting in a single stage,
simpler process with less catalyst and lower reactor volume, in
addition to providing high purity H
2
.
This technology requires a thin noble metal alloy membrane
to selectively permeate H with low mass transfer resistance in the
presence of competitive WGS co-reactants and contaminants,
especially hydrogen sulfide, H
2
S, and related sulfur-species. The
development of crack-free, high H-selectivity membranes that
are stable to thermal and pressure cycling and resistant to the
poisoning of surface H
2
adsorption and dissociation sites, is an
active area of research. It has been shown that below 350
◦
C,
the Pd
0.47
Cu
0.53
ordered body-centered cubic (B2) alloy has a
high H permeability and a reported tolerance to H
2
S [1]. How-
ever, implementation of this membrane alloy presents some
challenges. The Pd–Cu binary phase diagram in Fig. 1 shows
that while this composition occurs within the single B2 phase
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.01.130