Nanoporous Glass-Ceramics for Gas Separation

Abstract

The development of nanoporous gas separation membranes to extract H2 from a mixed fuel stream of CH4/H2O/CO2/CO is desirable for use in methane steam reforming reactions. Ni-containing cordierite glass-ceramics are candidate materials for this application. The final microstructure of these glass-ceramics includes two sieving mechanisms: (1) a 5 Å channel inherent to the cordierite crystal structure which grows normal to the surface of the glass, and (2) a nanoporous non-stoichiometric spinel in the bulk with theoretical pore diameters ranging from 4-8 Å. Through reaction with hydrogen we demonstrate the ability to form nanopores in NixMg1-xAl2O4 spinel. The stability limit for the non-stoichiometric spinel formed during the H2 reaction lies between 0.5_x_0.75. The formation of an equal number of nickel and oxygen vacancies in spinel is determined using Rietveld refinement of X-ray diffraction data and thermogravimetric analysis. These vacant sites form the nanopores in the defect spinel structure.