Keywords: palladium-silver membrane, hydrogen permeability, membrane reactors, surface reaction, co-existing gas, in situ observations, transport kinetics, hydrogen atmospheres, carbon monoxide
Surface reaction and transport kinetics of hydrogen through palladium-based membranes under gas co-existing with hydrogen atmospheres
In order to understand how gas co-existing with hydrogen affects the hydrogen permeability of a silver 23wt%-palladium membrane, the surface reaction of hydrogen was evaluated from the continuity of the surface reaction rate and the bulk diffusion flux of hydrogen based on the results of hydrogen-permeation measurements. The interference effect of the co-existing species was quantified as a function of temperature, partial pressure and the components of the co-existing gas. In order to investigate the behaviour of the co-existing species on the membrane surface, in situ observation using the Polarisation Modulated Infrared Reflection Absorption Spectroscopy (PM-IRRAS) was carried out. An infrared absorption peak due to the adsorption of carbon monoxide on the membrane was observed under the atmosphere of 7.8% carbon monoxide – 2.3% water vapour – 89.9% hydrogen. From the dependence of the infrared absorption peak on temperature, co-existing carbon monoxide was found to adsorb onto the membrane surface irreversibly.