Abstract: A catalyst for use in a process for the removal of nitrogen oxides from exhaust gases contaminated with dust in which the process uses ammonia. The catalyst is made of a material which is easily disposable. Furthermore, the catalyst should be completely used up in the catalysis. The catalyst comprises individual ceramic bricks with a porous surface, and passages therethrough for the flow of the exhaust gases. The bricks exhibit a resistance to abrasion which is designed so that the dust of the exhaust gas which flows through the passages erodes the catalyst surface, thereby reactivating the catalyst. The exhaust gas carries the dust and the eroded material along with it.

Abstract: In a process for the reactivation of a catalyst, which is used for the removal of NO.sub.x, oxides of nitrogen, from exhaust gases, the catalyst should be capable of easy reactivation. For this purpose, when the catalyst starts to lose its activity, it is exposed in a reducing atmosphere to a carbon monoxide current. In an apparatus for the execution of the process, the catalyst is placed in two separate chambers. The carbon monoxide stream is directed alternately to both chambers.

Abstract: A recuperator includes plural ceramic recuperator tubes arranged vertically on top of each other. Each tube has an outer periphery, first and second opposite ends, and a gas passage extending longitudinally between such ends. The first end includes an annular sealing surface extending radially inwardly from the periphery and an annular projection defined by a conical surface extending axially from the sealing surface to an end surface of the first end. The second end includes a square flange extending outwardly from the periphery and a stepped seal extending axially inwardly into the flange from an end surface of the second end.