There is provided a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A denitration catalyst molded in a block shape contains 43 wt % or more of vanadium pentoxide. The denitration catalyst has a BET specific surface area of 30 m.sup.2/g or more and is used for denitration at 200? C. or lower.

There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of removing a used denitration catalyst from a denitration device and then coating the used denitration catalyst with a catalyst component. The catalyst component contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more, and the denitration catalyst after recycling is used for denitration at 200? C. or lower.

There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of spraying an aqueous solution with a pH of 7 or more onto a used denitration catalyst while the denitration catalyst is set in a denitration device to remove a surface of the denitration catalyst. The denitration catalyst contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more. The denitration catalyst after recycling is used for denitration at 200? C. or lower.

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.

A catalyst article including a substrate with an inlet side and an outlet side, a first zone and a second zone, where the first zone includes an ammonia slip catalyst (ASC) comprising a platinum group metal on a support and a first SCR catalyst; where the second zone includes a catalyst selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC); and where the first zone is located upstream of the second zone. The first zone may include a bottom layer with a blend of: (1) the platinum group metal on a support and (2) the first SCR catalyst; and a top layer comprising a second SCR catalyst, the top layer located over the bottom layer.

A catalyst article including a substrate with an inlet end and an outlet end, a first zone and a second zone, where the first zone comprises: a) an ammonia slip catalyst (ASC) bottom layer comprising a platinum group metal on a support; and b) an SCR layer comprising a second SCR catalyst, the SCR layer located over the ASC bottom layer; where the second zone comprises a catalyst (second zone catalyst) selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC); wherein the ASC bottom layer extends into the second zone; and where the first zone is located upstream of the second zone. The ASC bottom layer may include a blend of: (1) the platinum group metal on a support and (2) a first SCR catalyst.

A SCR catalyst composition comprises a SCR catalyst; and a binder comprising a porous inorganic material, wherein the porous inorganic material comprises a disordered arrangement of delaminated layers, has a disordered porous structure, and has a multimodal pore size distribution comprising at least a first modal maximum having a macroporous or mesoporous pore size and a second modal maximum having a microporous pore size. The SCR catalyst composition can be manufactured using the method comprising the steps of: (i) providing an inorganic material having a layered structure; (ii) contacting the material with a cationic surfactant to form a swollen material; (iii) agitating the swollen material to form an agitated material; and (iv) calcining the agitated material to recover a delaminated inorganic material, wherein an SCR catalyst is mixed with the inorganic material prior to step (iv).

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

An exhaust gas purifying device includes a first SCR catalyst converter, an oxidation catalyst converter, a filter section, and a second SCR catalyst converter arranged in series to a flow direction of an exhaust gas. The first SCR catalyst converter includes a pillar-shaped honeycomb structure a cell density of which is from 31 to 78 cells/cm.sup.2, a porosity of the partition walls of which is from 50 to 65%, and in which a first SCR catalyst is loaded onto the surfaces of the partition walls and inner portions of pores formed in the partition walls, and an amount of the first SCR catalyst to be loaded onto the surfaces of the partition walls and the inner portions of the pores is from 200 to 500 g/L and an amount of the first SCR catalyst to be loaded onto the inner portions of the pores is from 5 to 80 g/L.

There is provided a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A denitration catalyst contains 3.3 wt % or more of vanadium oxide in terms of vanadium pentoxide and has a BET specific surface area of 10 m.sup.2/g or more.