Reactor and method for providing improved conversion of oxidizable pollutants from a waste gas stream by passing such a gas stream at a velocity of less than about 200 feet per minute through a chamber containing a thin catalyst bed capable of oxidizing the oxidizable pollutants and having a temperture rise from the inlet side to the outlet side of the bed of between about 50.degree. C. and about 400.degree. C. and a distributor plate located upstream and parallel to the bed. The distributor plate contains a plurality of openings such that the plate surface has a total open area of less than about 10% therein. In a preferred embodiment wherein a plurality of catalyst beds are provided, separate distributor plates are placed between the inlet for each bed and the bed itself.