Also alternatively,the gas which flows through the permanganate-impregnated zeolite crystals comprises one or more of hydrogen, nitrogen, ethylene, formaldehyde, and other gases similar to these gases (but not H.sub.2 S gas).In another preferred embodiment, the invention produces manganese dioxide-impregnated zeolite crystals from zeolite crystals impregnated with permanganate (with or without a Q