(288e) Hydrogen Permeation Through Pd Membranes with/without Deposited Cu Catalyst

Hydrogen permeation through Pd membranes with deposited Cu catalyst.

This study presents the fundamental aspects of hydrogen
transport through palladium membranes, with and without deposited catalyst
films. Understanding the transport through such systems is important for
properly analyzing and predicting the performance of membranes and associated
catalysts in catalytic membrane reactors. Hydrogen permeation was investigated
through palladium-based membranes under conditions that would be used in
applying them as catalytic membrane reactors. The potential for using
palladium-based membranes with deposited catalyst films as catalytic membrane
reactors is to improve reaction yield and selectivity for hydrogenation
reactions. Copper
catalysts were uniformly deposited on Pd membranes
with different geometries and thicknesses via electrodeposition
using a novel masking technique developed in this work. Deposition was as
continuous films or as islands on one side of the foils (permeates side). These
films (or islands) were annealed to cupric oxide that reduced to Cu, which
subsequently diffused into the membrane during long-time H₂
permeation studies (see Figure 1).

\s

Figure 1. 
SEM image of as-deposited Pd1CC60 foil

 Short-time and long-time transient studies after exposing the
membranes to various gas atmospheres and temperatures elucidated the effects of
the membrane ?history? on performance. The transient studies indicated that the
membrane structure changes during permeation (see Figure 2), resulting in
faster hydrogen permeation.

\s

Figure 2 SEM image of Pd1CC60 foil
after annealing followed by hydrogen permeation studies

Fluxes
through the uncoated Pd-3 were the highest, ranging from ~8
to 15 mmol/m².s. At the other
extreme, fluxes of ~0.5 to 1 mmol/m².s
were measured for the Pd1CC60; the thickest continuous film studied. The two Pd/Cu foils with islands (Pd1IsV60 and Pd1IsC7) had nearly
identical fluxes (see Figure 3) even though the deposition times were 60 and 7
seconds, respectively. Compare fluxes through the foils with continuous films,
it is clear that the flux decreases with Cu film thickness. Finally, fluxes
through all of these membranes followed Sieverts' law.

It
was concluded from this and other results that diffusivity in the membrane
material likely increases with hydrogen coverage for the conditions studied.

\s

Figure
3 Long-time H₂ fluxes through uncoated Pd-3 and Pd/Cu
foils at 473 K and feed pressures of 124, 138, 152, and 165 kPa
with permeate at 93 kPa