Degussa - Huls Ag

Wilfried Muller

Egbert Lox

Rainer Domesle

Thomas Kreuzer

Dieter Lindner

Wolfgang Strehlau

Jurgen Leyrer

A process is disclosed for operating an exhaust gas treatment unit for an internal combustion engine which is operated with lean normalized air/fuel ratios over most of the operating period. The exhaust gas treatment unit contains a nitrogen oxides storage catalyst with an activity window .DELTA.T.sub.NOX for the storage of nitrogen oxides at normalized air/fuel ratios of greater than 1 and release of the nitrogen oxides at normalized air/fuel ratios of less than or equal to 1 and a sulfur trap, located upstream of the nitrogen oxides storage catalyst, with a sulfur desorption temperature T.sub.S,DeSOx above which the sulfates stored on the sulfur trap are decomposed at normalized air/fuel ratios of less than or equal to 1. The nitrogen oxides contained in the exhaust gas are stored on the nitrogen oxides storage catalyst and the sulfur oxides are stored on the sulfur trap at normalized air/fuel ratios greater than 1 and exhaust gas temperatures T.sub.K within the activity window T.sub.NOX, wherein at the same time the exhaust gas temperature just upstream of the sulfur trap is lower than its sulfur desorption temperature T.sub.S,DeSOx. By cyclic lowering of the normalized air/fuel ratio in the exhaust gas to less than 1 the stored nitrogen oxides are released again from the storage catalyst. After each predetermined number N.sub.1 of nitrogen oxides storage cycles, sulfur is removed from the sulfur trap. This takes place by raising the exhaust gas temperature just upstream of the sulfur trap to above its sulfur desorption temperature T.sub.S,DeSOx and also lowering the normalized air/fuel ratio in the exhaust gas to less than 1.

Process for operating an exhaust gas treatment unit containing a sulfur

A catalyst for purifying the exhaust gases from diesel engines. The catalyst contains a zeolite mixture of several zeolites with different moduli and platinum group metals as well as further metal oxides from the group aluminum silicate, aluminum oxide and titanium oxide, wherein the aluminum silicate has a ratio by weight of silicon dioxide to aluminum oxide of 0.005 to 1 and the platinum group metals are deposited on only the further metal oxides.

Diesel catalytic converter

Growing community of inventors

Karben, Germany

Wilfried Muller