The effect of heat treatment in air on CO inhibition of a ∼3 μm Pd–Ag (23 wt.%) membrane

Abstract

Strong inhibitive effects of CO on hydrogen permeation through thin, Pd-based membranes have been found to exist. In this work, it is shown experimentally that the inhibition by CO was significantly reduced after heat treatment in air. A ∼3 μm thick Pd–Ag (23 wt.%) membrane was mounted in a microchannel configuration that allowed sweep gas and other transport effects to be eliminated. The CO inhibition was investigated at 300 and 350 °C before and after exposure to air at 300 °C for nearly five days, by determining the change in flux upon increasing CO concentration under constant hydrogen partial pressure. While the flux was decreased by ∼60% by going from 0 to 1 mol% CO at 350 °C before heat treatment in air, the reduction was only ∼15% after the treatment. This relative improvement under CO comes in addition to the intrinsic improvement in hydrogen permeance upon heat treatment in air. An approach combining a Sieverts–Langmuir model equation and microkinetic modelling (through transition state and unity bond index-quadratic exponential potential theories), indicates that the effect can be explained by changes in CO and H 2 heats of adsorption upon the treatment.