摘要:
A single-layered three-way catalytic converter containing palladium as the only catalytically active noble metal, with high activity and heat resistance. The catalyst contains, in addition to finely divided, stabilized aluminum oxide, at least one finely divided cerium/zirconium mixed oxide and optionally finely divided nickel oxide as well as highly dispersed amounts of cerium oxide, zirconium oxide and barium oxide. The palladium is distributed largely uniformly throughout the entire catalyst.
摘要:
A process of operating a nitrogen oxides storage catalyst of an exhaust gas treatment system is described. The process relates to the cycling of the normalized air/fuel ratio &lgr;-value of the exhaust gas exiting the engine, in which a lambda value greater than 1 represents oxygen-rich, lean burn conditions in which a sorption phase for the sorption of nitrogen oxides takes place; and in which a lambda value less than 1 represents oxygen-poor, rich burn conditions in which a desorption and conversion phase for the desorption and conversion of nitrogen oxides takes place. The &lgr;-value of the exhaust gas downstream from the storage catalyst is monitored during the desorption and conversion phase to determine the end of the desorption and conversion phase based on the &lgr;-value falling below a predetermined threshold value. Advantages of the process described include the ability to distinguish permanent from temporary damage to the nitrogen oxides storage catalyst, the ability to compensate for the slow deterioration in storage capacity, and the ability to determine when the storage capacity of the catalyst falls below a certain minimum capacity after which the storage catalyst must be either replaced or thermally treated while still installed in the exhaust gas treatment system.
摘要:
A process is disclosed for lowering nitrogen oxide levels in combustion engine exhaust gas by a reduction catalyst and by controlling the exhaust gas temperature upstream from the catalyst to a constant value, at which the catalyst exhibits maximum conversion for nitrogen oxides. It is possible to maintain maximum conversion over a wide range of engine outlet temperatures of the exhaust gas.
摘要:
The present invention provides a process and a device for regeneration of a nitrogen oxide storage catalyst in the exhaust system of a diesel engine. The process comprises a first and a second regeneration strategy. The first regeneration strategy is applied when the exhaust gas temperature is above a threshold value and comprises changing the air/fuel-ratio from a lean to a rich value during a first regeneration period. The second regeneration strategy is applied when the exhaust gas temperature is below a threshold value and comprises switching the air/fuel-ratio back and forth between lean and rich air/fuel-ratios, forming a sequence of between 2 and 10 rich pulses and between 2 and 10 lean pulses during a second regeneration period.
摘要:
The present invention relates to a method of removing nitrogen oxides from the exhaust gas of a lean-burn internal combustion engine by selective catalytic reduction (SCR) using ammonia. The exhaust gas is routed first over a platinum-containing pre-catalyst and then over an SCR catalyst. The ammonia needed for the selective catalytic reduction is added to the exhaust gas upstream of the pre-catalyst at an exhaust-gas temperature below 250° C., while it is supplied to the exhaust gas between the pre-catalyst and the SCR catalyst at an exhaust gas temperature above 150° C. By adopting this procedure, a very large temperature range for the selective catalytic reduction with high nitrogen conversion rates is obtained.
摘要:
The invention relates to a catalyst arrangement for purifying the exhaust gases of internal combustion engines operated under lean conditions. It is proposed that a thinwalled, porous carrier be coated on one side with a nitrogen oxide storage catalyst and on the other side with an SCR catalyst. When the exhaust gas is passed through the catalytic coatings and the support material, a significant improvement in the nitrogen oxide conversion is achieved compared to a series arrangement of the catalysts on separate carriers. Wall flow filters have been found to be useful as thin-walled carriers.
摘要:
An oxygen storage material comprising cerium oxide and at least one second oxide of a metal M1 is disclosed as well as a process for manufacturing the material and the use of this material in an exhaust gas cleaning catalyst. In a preferred embodiment the oxygen storage material comprises particles from a Ce/M1 mixed oxide solid solution coated with an oxide of another metal M2. Metal M1 e.g. can be calcium or zirconium while metal M2 most preferably is aluminum.
摘要翻译:公开了一种包含氧化铈和至少一种金属M 1 O 2的第二氧化物的储氧材料,以及用于制造材料的方法以及在废气清洁催化剂中使用该材料。 在优选的实施方案中,储氧材料包含涂覆有另一种金属M 2 O 2的氧化物的Ce / M 1混合氧化物固溶体的颗粒。 金属M 1,例如 可以是钙或锆,而金属M 2最优选是铝。
摘要:
A process for reducing the nitrogen oxides present in a lean exhaust gas from an internal combustion engine by selective catalytic reduction on a reduction catalyst using ammonia, wherein a fraction of the nitrogen monoxide present in the exhaust gas is oxidized to nitrogen dioxide before the exhaust gas, together with ammonia, is passed over the reduction catalyst. The reduction catalyst contains a zeolite exchanged with transition metals and oxidation of the nitrogen monoxide is performed in such a way that the exhaust gas contains 30 to 70 vol. % of nitrogen dioxide before contact with the reduction catalyst.
摘要:
A catalyst for reducing nitrogen oxides in oxidizing and reducing atmospheres which contains iridium on a support material. Silicon dioxide or a dealuminized zeolite in the acid H form with a modulus of more than 20, preferably more than 100, or mixtures thereof are used as support materials. Iridium is deposited on the external surfaces of these support materials with average particle sizes between 10 and 30 nm. The catalyst is particularly suitable for treating exhaust gases from lean-burn gasoline engines or from diesel engines.
摘要:
A process for reducing the nitrogen oxides content of the exhaust gas from an internal combustion engine includes treating the exhaust gas in an electric gas discharge such that at least one of nitrogen dioxide or nitric acid are formed from nitrogen oxides in the exhaust gas; storing the nitrogen dioxides and/or the nitric acid in the form of nitrates on a nitrogen oxides storage material during phases when the engine operates with a greater than a stoichiometric air/fuel ratio (i.e., the storage phase); decomposing the nitrates to give nitrogen oxides during brief phases when the engine operates with a less than the stoichiometric air/fuel ratio (i.e., the desorption phase); and reducing the nitrogen oxides which are released from the storage material to nitrogen. The nitrogen oxides storage material may be located in an electric gas discharge zone, and the exhaust gas may be passed through the discharge and then over the storage material.