Embodiments of the present disclosure may improve the accuracy of diagnosis in diagnosing whether an exhaust gas purification system having an SCR filter is faulty. It is determined that the exhaust gas purification system is faulty if the NOx removal rate with the SCR filter calculated using a measurement value of an NOx sensor is lower than or equal to a predetermined criterion removal rate. In the apparatus, a differential pressure change rate defined as the increase in a converted differential pressure value per unit increase in the filter PM deposition amount is calculated. The value of the criterion removal rate is set higher when the differential pressure change rate at the time when the measurement value of the NOx sensor is obtained is lower than a predetermined threshold than when the differential pressure change rate is higher than or equal to the predetermined threshold.

An exhaust aftertreatment system configured to reduce nitrous oxide (N.sub.2O) formation includes a first selective catalytic reduction (SCR) catalyst. The first SCR catalyst is configured for low N.sub.2O formation and low ammonia (NH.sub.3) storage capacity. A second SCR catalyst is positioned downstream of the first SCR catalyst. The second SCR catalyst is configured for high NH.sub.3 storage capacity.

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.

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 provided on at least a portion of said first surface, wherein the first layer comprises an ammonia slip catalyst composition comprising one or more platinum group metals supported on titania, a silica-titania mixed oxide, a CeZr mixed oxide, or a mixture thereof, and a second layer is provided on at least a portion of the first layer and comprises an SCR catalyst composition.

A selective catalytic reduction catalyst composition for converting oxides of nitrogen (NO.sub.x) in an exhaust gas using a nitrogenous reductant comprises a mixture of a first component and a second component, wherein the first component is an admixture of the H-form of an aluminosilicate mordenite zeolite (MOR) and an iron-promoted aluminosilicate MFI zeolite; and the second component is a vanadium oxide supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of both titania and silica-stabilized titania, wherein the weight ratio of the first component to the second component is 10:90 to 25:75.

To provide methods for efficiently producing an 8-membered oxygen ring zeolite and an AEI-type zeolite at a low cost, with an organic structure-directing agent that is inexpensive and easily available industrially without using an expensive organic structure-directing agent, such as a cyclic quaternary ammonium salt. A method for producing an 8-membered oxygen ring zeolite, the method comprising mixing an aluminum atom raw material, a silicon atom raw material, an alkali-metal atom raw material, an organic structure-directing agent, and water with one another in order to prepare a raw material mixture, and producing an 8-membered oxygen ring zeolite from the raw material mixture by hydrothermal synthesis, the aluminum atom raw material including at least an aluminosilicate zeolite having a framework including a composite building unit d6r defined by International Zeolite Association (IZA), the aluminosilicate zeolite having a framework density of 15 T/1000 .sup.3 or less, the silicon atom raw material including at least the aluminosilicate zeolite and a silicon atom raw material other than the aluminosilicate zeolite, the organic structure-directing agent including at least a quaternary ammonium salt including 5 to 11 carbon atoms per molecule.

An exhaust gas purification material according to the present invention is provided with a particulate filter 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 differs between an upstream portion of the filter including an exhaust gas inlet-side end, and an downstream portion of the filter including an exhaust gas outlet-side end. A maximum allowable adsorption amount of ammonia A in the upstream portion is smaller than a maximum allowable adsorption amount of ammonia B in the downstream portion (A<B).

A retention system for use with an aftertreatment module is disclosed. The retention system may include a first support mat disposed on at least one surface of the at least one catalyst substrate. The retention system may also include at least one support plate having a corrugated portion disposed on the first support mat. The retention system may further include a second support mat disposed on the corrugated portion.

The present invention is directed to a catalyst system for the reduction of the harmful exhaust-gas constituents hydrocarbons (THC), carbon monoxide (CO), nitrogen oxides (NO.sub.x), and the environmentally detrimental secondary emissions ammonia (NH.sub.3) and nitrous oxide (N.sub.2O) of combustion engines operated using gasoline and to a corresponding method for exhaust-gas purification. The system is characterized by a particular arrangement of catalysts and is used in the case of engines which are operated with predominantly, on average, stoichiometric air/fuel mixtures. Here, a three-way catalyst produced in accordance with the current prior art is preferably installed in a close-coupled position. In the underfloor position, there is situated an SCR catalyst produced in accordance with the current prior art, followed by a further three-way catalyst produced in accordance with the current prior art. The three-way catalyst in the underfloor region furthermore has a lower oxygen-storing capacity than the close-coupled three-way catalyst.

A retention system for use with an aftertreatment module is disclosed. The retention system may include a first support mat disposed on at least one surface of the at least one catalyst substrate. The retention system may also include at least one support plate having a corrugated portion disposed on the first support mat. The retention system may further include a second support mat disposed on the corrugated portion.