A method of selectively catalysing the reduction of oxides of nitrogen (NO.sub.x) including nitrogen monoxide in an exhaust gas of a stationary source of NO.sub.x emissions also containing oxides of sulfur (SO.sub.x) comprising the steps of passively oxidising nitrogen monoxide to nitrogen dioxide (NO.sub.2) over an oxidation catalyst comprising a platinum group metal so that a NO.sub.2/NO.sub.x content is from 40-60%; introducing a nitrogenous reductant into the exhaust gas; and contacting exhaust gas having the 40-60% NO.sub.2/NO.sub.x content and containing the nitrogenous reductant with a selective catalytic reduction (SCR) catalyst comprising an aluminosilicate zeolite promoted with copper.

An exhaust system for treating an exhaust gas from an internal combustion engine is disclosed. The system comprises a modified lean NO.sub.x trap (LNT), a urea injection system, and an ammonia-selective catalytic reduction catalyst. The modified LNT comprises a first layer and a second layer. The first layer comprises a NO.sub.x adsorbent component and one or more platinum group metals. The second layer comprises a diesel oxidation catalyst zone and an NO oxidation zone. The diesel oxidation catalyst zone comprises a platinum group metal, a zeolite, and optionally an alkaline earth metal. The NO oxidation zone comprises a platinum group metal and a carrier. The modified LNT stores NO.sub.x at temperatures below about 200° C. and releases at temperatures above about 200° C. The modified LNT and a method of using the modified LNT are also disclosed.

Described are compositions and catalytic articles comprising both a first molecular sieve promoted with copper and a second molecular sieve promoted with iron, the first and second molecular sieves having a d6r unit and the first molecular sieves having cubic shaped crystals with an average crystal size of about 0.5 to about 2 microns. The weight ratio of the copper-promoted molecular sieve to the iron-promoted molecular sieve can be about 1:1 to about 4:1. The catalytic articles are useful in methods and systems to catalyze the reduction of nitrogen oxides in the presence of a reductant.

Provided is a system for treating a flowing exhaust gas comprising a lean NOx trap, a catalyzed soot filter, an ammonia or an ammonia precursor metering system for metering ammonia or an ammonia precursor into the flowing exhaust gas; and an SCR catalyst, wherein the SCR catalyst is disposed downstream of the lean NOx trap and comprises copper and/or iron supported on a small pore molecular sieve.

Described are catalyst materials and catalytic articles comprising a metal exchanged SAPO material comprising a plurality of substitutional sites consisting essentially of Si(4Al) sites and substantially free of Si(0Al) sites. The materials and catalytic articles are useful in methods and systems to catalyze the reduction of nitrogen oxides in the presence of a reductant.

A catalyst fibrous structure having a catalyst metal carried on a fibrous structure, wherein (a) a Log differential micropore volume distribution curve thereof obtained by measurement using a mercury intrusion technique has a peak having a maximum micropore diameter in the range of from 0.1 μm to 100 μm; (b) a Log differential micropore volume at the peak is 0.5 mL/g or more; and (c) an amount of a catalyst metal compound and a binder carried per unit volume is 0.05 g/mL or more. A production method for producing a catalyst fibrous structure having: (1) mixing a catalyst metal compound or a catalyst precursor, and an inorganic binder and a solvent; (2) grinding the mixture to obtain a coating material of the catalyst metal compound or the catalyst precursor having a median particle diameter of 2 μm or less and a viscosity of from 10 mPa.Math.s to 200 mPa.Math.s; (3) impregnating a fibrous structure with the coating material to fill up voids of the fibrous structure with the coating material of the catalyst metal compound or the catalyst precursor; (4) heating and drying the fibrous structure, directly as it is, at a temperature not lower than the boiling point of the solvent; and (5) heating and calcination the dried fibrous structure at a temperature not lower than the dehydration temperature of the inorganic binder to obtain a catalyst fibrous structure.

A catalyst article having an extruded support having a plurality of channels through which exhaust gas flows during operation of an engine, and a single layer coating or a bi-layer coating on the support, where the extruded support contains a third SCR catalyst, the single layer coating and the bilayer-coating contain platinum on a support with low ammonia storage and a first SCR catalyst. 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 composition comprising a mixture of (a) a zeolite compound in an amount of from 10% to 60% by weight, wherein the zeolite compound comprises cations selected from Fe.sup.2+, Fe.sup.3+, Cu.sup.+, Cu.sup.2+ or mixtures thereof, and (b) a ceria/zirconia/alumina composite oxide, wherein the alumina content in said composite oxide is in the range of 20 to 80% by weight, in particular of 40 to 60% by weight,
a catalyst comprising such catalyst composition and its use for exhaust gas after-treatment of diesel and lean burn engines.

A selective catalytic reduction (SCR) catalyst includes a support layer. A copper-loaded chabazite (Cu/CHA) layer is supported on the support layer. A copper-loaded beta zeolite (Cu/beta) is supported on the Cu/CHA layer. The Cu/beta may be hydrothermally pre-aged prior to use of the SCR catalyst in a vehicle. The pre-aged Cu/beta is essentially free of phosphorous (P), calcium (Ca), zinc (Zn), sodium (Na), potassium (K), magnesium (Mg), iron (Fe), CaSO.sub.4, Ca.sub.19Zn.sub.2(PO.sub.4).sub.14, CaZn.sub.2(PO.sub.4).sub.2, ash, and/or soot.

Hydrocarbon (HC) traps are disclosed. The HC trap may include a first zeolite material having an average pore diameter of at least 5.0 angstroms and configured to trap hydrocarbons from an exhaust stream and to release at least a portion of the trapped hydrocarbons at a temperature of at least 225° C. The HC trap may also include a second zeolite material having an average pore diameter of less than 5.0 angstroms or larger than 7.0 angstroms. One or both of the zeolite materials may include metal ions, such as transition, Group 1A, or platinum group metals. The HC trap may include two or more discrete layers of zeolite materials or the two or more zeolite materials may be mixed. The multiple zeolite HC trap may form coke molecules having a relatively low combustion temperature, such as below 500° C.