Method for applying porous, metal oxide coatings to relatively nonporous fibrous substrates

A method for the preparation of a catalytically active flexible fibrous element comprised of a porous, catalytically active layer of at least one metal oxide coated on, and disposed as the external surface of, a flexible fibrous substrate of substantially non-porous fibers having surface hydroxyl groups selected from the group consisting of glass and ceramic fibers, said method including the steps of

• a. preparing a coating solution of at least one substantially unhydrolyzed hydrolyzable metal alkoxide precursor of said at least one catalytically active metal oxide dissolved in a substantially anhydrous organic solvent;
• b. applying a thin, substantially uniform layer of said coating solution on a contaminant free surface of said non-porous fibrous substrate;
• c. drying said coated substrate in the presence of water or water vapor in a manner so as to initiate hydrolysis of said metal alkoxide to the corresponding metal hydroxide and condensation thereof to the corresponding metal oxide;
• and
• d. curing said coated substrate initially in a microwave oven and thereafter further curing in a thermal oven at a temperature in the range of between about 250.degree. C. and about 500.degree. C. so as to drive said hydrolysis and condensation reactions substantially to completion, and to substantially remove the organic constituents from said coated substrate and form said element, said curing being done at a temperature less than that which will cause a substantial loss of catalytic activity.