Preparation of palladium-silver alloy membranes for hydrogen separation by the spray pyrolysis method

A Pd-Ag alloy membrane is formed on the outer surface of a porous alumina hollow-fiber support by spray pyrolysis of a Pd(NO3)2 and AgNO3 solution in a H2-O2 flame. The mass fraction of silver in the membrane obtained at a support-surface temperature of 1240–1340 K is as low as 0.04, while its fraction in the total metal mass dissolved in the spray solution is 0.1–0.4. This is explained by the higher partial pressure of silver compared to that of palladium. An additional spray pyrolysis with a silver nitrate solution provides a proper silver content in the alloy membrane. The thickness of the alloy membrane is 1.5–2 μm, and the separation factor of hydrogen to nitrogen is about 24 at 773 K. The membrane surface is observed by high-resolution SEM, and the evolution of the morphology is discussed from the view of the deposition mechanism.

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