Work will be presented describing the preparation of an inorganic membrane with permeability for H2 higher than palladium and with greater than 99.9% selectivity over larger species like CO, CO2 and CH4. The membrane is a composite formed by the deposition of a thin, 20 nm SiO2 layer on a specially designed alumina support. The alumina support is obtained by the deposition of boehmite sols of controlled size on top of a porous substrate, so as to create a graded structure with increasingly small pore sizes. The permeation of the small gas species, H2, He, and Ne through the silica layer is analyzed in detail in order to obtain insight about the transport mechanism and the structure of the silica. The order of permeance through the silica layer is highly unusual, He &gt; H2 &gt; Ne, following neither molecular weight nor size. The order of permeation is quantitatively explained using a theory derived from statistical mechanics, which takes into consideration the density of solubility sites for the various species and the vibrational frequency of the species within the sites. The theory allows obtention of the vibrational frequency (1.2x1013 s-1), solubility site density (3.7x1026 m-3 for H2) and the average distance between sites (0.84 nm) in the membrane. This is the first time an inorganic membrane has been described in detail at the nanometer level. The new membranes are used to illustrate several important novel concepts in membrane reactor (MR) science.

Nanostructure of a high-permeability, hydrogen-selective inorganic membrane

255th National Meeting (2018)

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