Abstract: An apparatus for the thermal-catalytic abatement of hydrocarbons, carbon monoxide, nitrogen oxides and particulates from effluent gas streams. The apparatus has a preheat section wherein the effluent is heated to 400.degree.-1000.degree. F by hot combustion gases. The effluent and combustion gases are directed by a baffle through a filter where combustible particulates are incinerated and noncombustible particulates are collected. The baffle followed by a diffuser cone, axially located on the filter, intimately mixes the effluent with the combustion gases so as to provide uniform flow and temperature distribution of the mixed gases across the filter. The filtered gases then pass through a catalytic reactor section containing a catalyst, preferably catalyst-coated ceramic honeycombs. In the presence of the catalysts the hydrocarbons and carbon monoxide in the heated gas stream are oxidized to carbon dioxide and water and the nitrogen oxides are reduced.