Abstract: A crystalline, silica platinum catalyst structure is provided by soaking a hydrophobic, high surface area, crystalline silica (SiO.sub.2) lattice essentially free of aluminum oxide in the SiO.sub.2 lattice, such as silicalite in an aqueous solution of Pt(NH.sub.3).sub.4 Cl.sub.2 and then, drying, reducing and cooling the crystalline silica to leave, catalyst crystallites of platinum on the crystalline silica and in the pores thereof, and then providing an outer, porous, membrane coating of high molecular weight, organic polytetrafluoroethylene, polymeric material on the coated crystallites. The platinized, crystalline silica may be slurried with, polytetrafluoroethylene and a ceramic support coated with the slurry, so that a water repellent, water vapor and hydrogen or oxygen gas permeable, polytetrafluoroethylene matrix is provided on the support with the platinized, crystalline silica dispersed in the matrix.