Conversion of nitrogen oxides

Zeolite catalyzed reduction of nitrogen oxides in exhaust gases is conducted with catalytic elements in the form of multi-channel structures in which parallel channels are defined by thin walls constituted by refractory oxides having zeolite dispersed therein and accessable to diffusion from surfaces of the channel walls. Such structures, preferably monolithic honeycomb forms, are prepared by calcining extruded or cast forms or kaolin at elevated temperatures and treating the calcined kaolin honeycomb with a caustic solution to develop a desired zeolite within the wall members and etch the wall surfaces to provide diffusion paths to and from the embedded zeolite. Such structures are peculiarly suited to high space velocity processes such as reduction of nitrogen oxides in providing for protection of the zeolite catalyst against erosion by high velocity gas streams while also providing adequate diffusivity for reactants at the high space velocities typical of the known reaction between oxides of nitrogen and a reducing agent such as ammonia.