An exhaust emission control system of an engine, including an 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, is provided. The system includes an SCR catalyst disposed in the exhaust passage downstream of the NO.sub.x catalyst and for purifying NO.sub.x within exhaust gas by causing a reaction with ammonia, a controller executing a NO.sub.x reduction controlling module for executing a control in which the air-fuel ratio is controlled to a target air-fuel ratio so that the stored NO.sub.x is reduced, and an ammonia adsorption amount acquiring module for acquiring an ammonia adsorption amount of the SCR catalyst by detection or estimation. The NO.sub.x reduction controlling module controls the target air-fuel ratio to be leaner as the ammonia adsorption amount increases.

An exhaust emission control system of an engine including a NO.sub.x catalyst disposed in an exhaust passage and 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, is provided. The system includes a SCR catalyst disposed downstream of the NO.sub.x catalyst and for purifying NO.sub.x by causing a reaction with ammonia, and a processor configured to execute a NO.sub.x reduction controlling module for controlling the air-fuel ratio to a target ratio so that the stored NO.sub.x is reduced. The controlling module limits the performance of the NO.sub.x reduction control when a temperature of the SCR catalyst is above a given temperature and loosens the limitation in a given engine operating state in which an exhaust gas flow rate is above a given rate despite the SCR catalyst temperature.

Catalysts having a blend of platinum on a support with low ammonia storage with a Cu-SCR catalyst or an Fe-SCR catalyst are disclosed. The catalysts can also contain one or two additional SCR catalysts. The catalysts can be present in one of various configurations. Catalytic articles containing these catalysts are disclosed. The catalytic articles are useful for selective catalytic reduction (SCR) of NOx in exhaust gases and in reducing the amount of ammonia slip. Methods for producing such articles are described. Methods of using the catalytic articles in an SCR process, where the amount of ammonia slip is reduced, are also described.

A catalyst article for treating a flow of a combustion exhaust gas comprises: a catalytically active substrate comprising one or more channels extending along an axial length thereof through which, in use, a combustion exhaust gas flows, the one or more channels having a first surface for contacting a flow of combustion exhaust gas; wherein the substrate is formed of an extruded vanadium-containing SCR catalyst material, wherein a first layer is disposed on at least a portion of the first surface, wherein the first layer comprises a washcoat of an ammonia slip catalyst composition comprising one or more platinum group metals supported on a particulate metal oxide support material, and wherein a layer comprising a washcoat of SCR catalyst composition is disposed on a surface in the one or more channels, wherein at least the portion of the first surface on which the first layer is disposed comprises a compound of copper, iron, cerium or zirconium or a mixture of any two or more thereof.

Described herein are illustrative exhaust systems and methods including ammonia generation and storage. An illustrative system can include a first exhaust conduit to and receive a first exhaust stream from a first engine, and a second exhaust conduit to and receive a second exhaust stream from a second engine. In the illustrative example, an exhaust treatment device coupled to the second exhaust conduit downstream of the second engine can convert nitrogen oxides (NO.sub.x) in the second exhaust stream into ammonia. An ammonia storage device coupled to the second exhaust conduit downstream of the exhaust treatment device can be configured to receive and store at least a portion of the converted ammonia as stored ammonia and to release at least a portion of the stored ammonia to a catalytic converter. The catalytic converter can include a selective catalytic reduction catalyst configured to use the ammonia to reduce NO.sub.x.

A radio frequency system and method for monitoring an engine-out exhaust emission constituent. The system comprises a housing containing the emission constituent, one or more radio frequency sensors extending into the housing and transmitting and receiving radio frequency signals, and a control unit for controlling the radio frequency signals and monitoring changes in the emission constituent based on changes in one or more parameters of the radio frequency signals. In one embodiment, the control unit measures a rate of change in one or more of the parameters of the radio frequency signals for monitoring a rate of change of the emission constituent including for example the emission rate, accumulation rate, and/or depletion rate of the emission constituent.

Provided is a method for producing an inexpensive, high-performance AEI type zeolite and an AEI type zeolite having a Si/Al ratio of 6.5 or less by using neither an expensive Y type zeolite as a raw material nor dangerous hydrofluoric acid. The method for producing an AEI type zeolite having a Si/Al ratio of 50 or less includes: preparing a mixture including a silicon atom material, an aluminum atom material, an alkali metal atom material, an organic structure-directing agent, and water; and performing hydrothermal synthesis of the obtained mixture, in which a compound having a Si content of 20% by weight or less and containing aluminum is used as the aluminum atom material; and the mixture includes a zeolite having a framework density of 14 T/1000 .sup.3 or more in an amount of 0.1% by weight or more with respect to SiO.sub.2 assuming that all Si atoms in the mixture are formed in SiO.sub.2.

An exhaust gas purification material according to the present invention is provided with a particulate filter 10 that traps particulate matter in exhaust gas and contains an SCR catalyst for adsorbing ammonia and reducing NOx in the exhaust gas. A maximum allowable adsorption amount of ammonia adsorbable by the filter 10 differs between an upstream portion 10a of the filter 10 including an exhaust gas inlet-side end 10c, and a downstream portion 10b of the filter 10 including an exhaust gas outlet-side end 10d. The SCR catalyst contained in the upstream portion 10a and the SCR catalyst contained in the downstream portion 10b are qualitatively different. A ratio (B/A) of a maximum allowable adsorption amount of ammonia A in the upstream portion 10a and a maximum allowable adsorption amount of ammonia B in the downstream portion 10b satisfies the relationship 1.1(B/A)2.

An aftertreatment assembly includes a selective catalytic reduction (SCR) device having a catalyst and configured to receive an exhaust gas. A controller is operatively connected to the SCR device. The controller having a processor and a tangible, non-transitory memory on which is recorded instructions for executing a method of model-based monitoring of the SCR device. The method relies on a physics-based model that may be implemented in a variety of forms. The controller is configured to obtain at least one estimated parameter, and at least one threshold parameter based at least partially on a catalyst degradation model. The catalyst degradation model is based at least partially on a predetermined threshold storage capacity (.sub.T). A catalyst status is determined based on a comparison of the estimated and threshold parameters. The operation of the assembly is controlled based at least partially on the catalyst status.

A method, control system, and vehicle system configured to control a selective catalyst reduction (SCR) system subtracts an amount of NO.sub.x present in a tailpipe upstream of the SCR system from an amount of NO.sub.x present in the tailpipe downstream of the SCR injector. A cumulative difference may be determined based on integrating the subtracted NO.sub.x value. The method, control system, and vehicle system are configured to determine whether the cumulative difference exceeds a control threshold, and to set a selected upstream NO.sub.x value as a predetermined model upstream NO.sub.x amount if the cumulative difference exceeds the control threshold, but to set the selected upstream NO.sub.x value as the determined upstream NO.sub.x amount if the cumulative difference does not exceed the control threshold. Thus, the system is reset to the model when downstream NO.sub.x values exceed upstream NO.sub.x values above a threshold, to bring the system back within control.