Processes for manufacturing nitrogen oxide storage materials and lean NOx trap catalysts are disclosed. Also disclosed are nitrogen oxide storage material made by processes comprising barium carbonate (BaCO.sub.3) and ceria (CeO.sub.2) by using Ba(OH).sub.2 instead of most or all Ba(OOCH.sub.3).sub.2 to reduce cost and reduce harmful byproducts. Aspects of the present invention also relate generally to lean NO.sub.x trap (LNT) comprising nitrogen oxide storage materials.

The invention relates to a catalyst system for reducing nitrogen oxides, which comprises a nitrogen oxide storage catalyst and an SCR catalyst, wherein the nitrogen oxide storage catalyst consists of at least two catalytically active washcoat layers on a supporting body, wherein a lower washcoat layer A contains cerium oxide, an alkaline earth compound and/or alkali compound, as well as platinum and palladium, and an upper washcoat layer B, which is arranged over the washcoat layer A, contains cerium oxide, platinum and palladium, and no alkali compound and no alkaline earth compound. The invention also relates to a method for converting NOx in exhaust gases of motor vehicles that are operated by means of engines that are operated in a lean manner.

An exhaust emission control system of an engine is provided, which includes a NO.sub.x catalyst disposed in an exhaust passage for storing NO.sub.x within exhaust gas when an air-fuel ratio of the exhaust gas is lean, and reducing the stored NO.sub.x when the air-fuel ratio is approximately stoichiometric or rich. A processor executes a NO.sub.x reduction controlling module for performing a NO.sub.x reduction control in which a fuel injector performs a post injection to control the air-fuel ratio to a target ratio, and an EGR controlling module for controlling an EGR valve to recirculate EGR gas. In the NO.sub.x reduction control, the EGR controlling module controls an opening of the EGR valve to a target opening smaller than when the NO.sub.x reduction control is not performed. The NO.sub.x reduction controlling module starts the control after the EGR valve opening is controlled to the target opening.

A passive NO.sub.X adsorbent includes: palladium, platinum or a mixture thereof and a mixed or composite oxide including the following elements in percentage by weight, expressed in terms of oxide: 10-90% by weight zirconium and 0.1-50% by weight of least one of the following: a transition metal or a lanthanide series element other than Ce. Although the passive NO.sub.X adsorbent can include Ce in an amount ranging from 0.1 to 20% by weight expressed in terms of oxide, advantages are obtained particularly in the case of low-Ce or a substantially Ce-free passive NOx adsorbent.

A NOx adsorber catalyst for treating an exhaust gas from a diesel engine. The NOx adsorber catalyst comprises a first region comprising a NOx adsorber material comprising a first molecular sieve catalyst. The first molecular sieve catalyst comprises a first noble metal and a first molecular sieve, and the first molecular sieve contains the noble metal. The first molecular sieve has an STI Framework Type.

An exhaust gas control apparatus for an internal combustion engine includes a NO.sub.x storage reduction catalyst, a selective catalytic reduction catalyst, and an electronic control unit configured to shift an operation state of the engine from a rich operation state to a lean operation state, in a case where an acquired temperature of the NO.sub.x storage reduction catalyst is higher than a storage limit temperature, and an acquired NH.sub.3 adsorption amount is equal to or larger than a lower limit adsorption amount when a lean operation restart request is made, and not to shift the operation state from the rich operation state to the lean operation state in a case where the acquired temperature of the NO.sub.x storage reduction catalyst is higher than the storage limit temperature and the acquired NH.sub.3 adsorption amount is smaller than the lower limit adsorption amount when the lean operation restart request is made.

The present invention relates to a nitrogen oxide storage catalyst composed of at least two catalytically active washcoat layers on a support body, wherein a lower washcoat layer A comprises cerium oxide, an alkaline earth metal compound and/or an alkali metal compound, and platinum and palladium, and an upper washcoat layer B disposed atop the washcoat layer A comprises cerium oxide, platinum and palladium, and no alkali metal or alkaline earth metal compound, and to a method of converting NO.sub.x in exhaust gases from motor vehicles which are operated with lean-burn engines.

An exhaust gas flow after-treatment (AT) system includes first AT device and a second AT device in fluid communication with and positioned in the flow of exhaust gas downstream of the first AT device. The AT system also includes an exhaust passage for carrying the flow of exhaust gas from the first AT device to the second AT device and an injector for introducing a reductant into the exhaust passage. The AT system additionally includes a variable-position mixer arranged within the exhaust passage downstream of the injector. Furthermore, the AT system includes a mechanism configured to regulate the variable-position mixer between and inclusive of a first mixer position configured to increase a swirling motion and turbulence in the exhaust gas flow within the exhaust passage to thereby mix the reductant with the exhaust gas flow, and a second mixer position configured to reduce a backpressure generated by the mixer.

A control apparatus is applicable to an internal combustion engine having an exhaust passage arranged with an NSR catalyst and an SCR catalyst, wherein when it is necessary to decrease NH.sub.3 adsorbed to the SCR catalyst, then an air-fuel ratio of an air-fuel mixture to be combusted in the internal combustion engine is controlled to a predetermined lean air-fuel ratio which is higher than a theoretical air-fuel ratio if a temperature of the SCR catalyst is not less than a lower limit temperature at which NH.sub.3 can be oxidized, while the air-fuel ratio of the air-fuel mixture to be combusted in the internal combustion engine is controlled to a predetermined weak lean air-fuel ratio which is lower than the predetermined lean air-fuel ratio and which is higher than the theoretical air-fuel ratio if the temperature of the SCR catalyst is less than the lower limit temperature.

A process of manufacturing a chabazite-type zeolite is provided having high heat resistance without having a large crystal size. A catalyst is also provided that contains such a chabazite-type zeolite and exhibits high nitrogen oxide reduction properties, and in particular high nitrogen oxide reduction properties in low temperatures below 200 C., even after exposure to high temperature and high humidity. A chabazite-type zeolite is provided having a silica to alumina molar ratio of no less than 15, a silanol group to silicon molar ratio of no more than 1.610.sup.2, an average crystal size of 0.5 m to less than 1.5 m, and a ratio of 50%-volume particle size to 10%-volume particle size of no more than 3.2. The chabazite-type zeolite preferably contains at least one of copper and iron.