The influence of heat treatment on the thermal stability of Pd composite membranes

In this work, the influence of high temperature heat treatments (>640 °C) on the thermal stability of Pd composite membranes was investigated. Several Pd composite membranes (<7 µm thick) were deposited by the electroless plating method onto the outer diameter of two different types of tubular porous supports. These membranes were subjected to different high temperature annealing processes and the thermal stability and microstructural evolution were studied. It was found that employing such heat treatments improved the thermal stability of the membranes when operated at lower temperatures; evidenced by a suppression of the rate at which hydrogen selectivity toward nitrogen declined over time at a given temperature. Heat pretreatment was also found to produce similar desirable effects under synthetic water gas shift mixtures containing up to 5 mol% CO. SEM images of the microstructural evolution as a function of temperature revealed that porosity that is typically present in as-deposited electroless plated films is significantly reduced after heat treatment.