This study reports the poisoning effect of co-existing N on H permeation through Pd composite membranes, consisting of thin Pd layers supported on α-Al2O3 hollow fibers. Hydrogen permeation of the composite membranes was measured at 623 to 773K for pure gas permeation in sequence of H, N and H and for mixture gas separation of equimolar H2/N2. The composite membranes were defect-free and gave high H permeance of 31.2m3/m2hbar at 773K. However, when the H2 activated composite membranes were exposed to N for a certain time, the followed H permeance decreased in comparison with the original value. The degree of decrease increased with decreasing temperature and with exposure time. Furthermore, when the composite membranes were exposed to the mixture feed of equimolar H2/N2 with certain total flow rate at 673 to 723K, the H flux on the permeate side kept stable only for several 100min then decreased gradually to some extent. And significant reduction could be obtained during the followed pure H permeance test in comparison with the original value for the fresh membranes. Fortunately, no additional defects were formed on the Pd layers during these processes and the deactivations of the composite membranes were reversible. A certain-time H treatment at 773K was sufficient to regenerate the deactivated membranes. The blocking of the active sites on Pd surface for H diffusion by the formed N-containing species (NHx, x = 0–2) was responsible for the deactivation of the membranes in the suggested deactivation mechanism.

The Effect of Co-Existing Nitrogen on Hydrogen Permeation through Thin Pd Composite Membranes. W.Wang, X.Pan, X.Zhang, W.Yang, G.Xiong: Separation and Purification Technology, 2007, 54[2], 262-71