Abstract: A method comprising subjecting fuel to combustion while the combustion atmosphere of the fuel is oscillated periodically and alternately between rich and lean conditions, leading the exhaust gas formed to a catalytic reactor, and bringing the exhaust gas into contact with a catalyst in the catalytic reactor to conduct catalytic reduction of nitrogen oxides contained in the exhaust gas, wherein the catalyst comprises as catalyst components: (A) an oxide catalyst component A comprising (a) ceria or (b) praseodymium oxide or (c) a mixture of oxides and/or a composite oxide of at least two elements selected from cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; and (B) (d) a noble metal catalyst component B selected from platinum, rhodium, palladium and oxides thereof; under an oxygen concentration adjusted to the range of 0.1-1.0% at the exit of the catalytic reactor under the rich conditions.

Abstract: The invention provides a catalyst for catalytic reduction of nitrogen oxides contained in exhaust gases wherein fuel is supplied and subjected to combustion under periodic rich/lean conditions and the resulting exhaust gases are brought into contact therewith, which catalyst comprises: (A) a catalyst component A comprising (c) ceria or (d) praseodymium oxide or (e) an oxide and/or a composite oxide of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; (B) a catalyst component B comprising (d) a noble metal catalyst component selected from the group consisting of platinum, rhodium, palladium and oxides thereof and (e) a carrier; and (C) a catalyst component C comprising (f) a solid acid, and (g) a solid acid supporting an oxide of at least one element selected from the group consisting of vanadium, tungsten, molybdenum, copper, iron, cobalt, nickel and manganese.

Abstract: The invention provides a catalyst and a catalyst structure for catalytic reduction of nitrogen oxides contained in exhaust gas wherein fuel is supplied and subjected to combustion under periodic rich/lean conditions and the resulting exhaust gases are brought into contact therewith, which catalyst comprises: an outer catalyst layer comprising an outer catalyst component A which comprises at least one selected from a solid acid, and a solid acid supporting oxides and/or ions of at least one element selected from vanadium, tungsten, molybdenum, copper, iron, cobalt, nickel and manganese, and an inner catalyst layer comprising an inner catalyst component which comprises at least one noble metal catalyst component B selected from platinum, rhodium, palladium and an oxide thereof and a catalyst component C comprising ceria or praseodymium oxide or a mixture of oxides and/or a composite oxide of at least two elements selected from cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lant

Abstract: A method which comprises subjecting fuel to combustion while the combustion atmosphere of the fuel is oscillated periodically and alternately between rich and lean conditions, leading the exhaust gas formed to a catalytic reactor, and bringing the exhaust gas into contact with a catalyst in the catalytic reactor to conduct catalytic reduction of nitrogen oxides contained in the exhaust gas, wherein the catalyst comprises as catalyst components: (A) an oxide catalyst component A comprising (a) ceria or (b) praseodymium oxide or (c) a mixture of oxides and/or a composite oxide of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; and (B) (d) a noble metal catalyst component B selected from the group consisting of platinum, rhodium, palladium and oxides thereof; under an oxygen concentration adjusted to be in the range of 0.1-1.0% at the exit of the catalytic reactor under the rich conditions.

Abstract: The invention provides a catalyst for catalytically reducing nitrogen oxides in diesel engine exhaust gas by use of unburnt carbon contained in the diesel engine exhaust gas as a reducing agent, the catalyst comprising: (a) alumina, or (b) alumina supporting an ion and/or an oxide of at least one transition metal selected from the elements of Period 4 of the Periodic Table, or (c) alumina supporting an aluminate of at least one transition metal selected from the elements of Period 4 of the Periodic Table.

Abstract: The invention provides a catalyst for catalytically reducing nitrogen oxides in diesel engine exhaust gas by use of unburnt carbon contained in the diesel engine exhaust gas as a reducing agent, the catalyst comprising: (a) an acid zeolite, or (b) an alkali metal- and/or alkaline earth metal-containing zeolite, or (c) a rare earth metal-containing zeolite, or (d) a zeolite containing at least one transition metal selected from Fe, Co, Ni and Cu.

Abstract: An emission gas purification system is provided capable of making EM clearer and further improving NOx purification capacity. An emission gas purification system 1 is provided for an exhaust system of an engine 3, and includes a purification unit 16 having a catalyst for purifying NOx according to an air-fuel ratio of an emission gas, and an air-fuel ratio control unit 2 adjusting the air-fuel ratio of the emission gas supplied to the purification unit 16. The air-fuel ratio control unit 2 purifies the emission gas by setting the emission gas A/F to be near stoichiometric or rich by reducing an intake air mass in an air-fuel mixture.

Abstract: An exhaust gas purifying device for an internal combustion engine, comprises: an exhaust purifying catalyst; a NOx purifying catalyst disposed downstream of the exhaust purifying catalyst; upstream and downstream A/F detecting sensors disposed on upstream and downstream sides of the exhaust purifying catalyst, respectively; means for supplying a reducing agent to the NOx purifying catalyst when conducting a reduction control of the NOx; means for calculating an amount of reduced NOx in the NOx purifying catalyst; means for terminating the reduction control when the amount of reduced NOx exceeds a prescribed reduction termination threshold value; means for detecting a degree of deterioration of the exhaust purifying catalyst based on an output from the upstream and downstream A/F detecting sensors; a threshold value correcting means for correcting the reduction termination threshold value according to the degree of deterioration of the exhaust purifying catalyst; and a correction prohibiting means for prohibit

Abstract: The invention provides a catalyst for catalytic reduction of nitrogen oxides contained in exhaust gases wherein fuel is supplied and subjected to combustion under periodic rich/lean conditions and the resulting exhaust gases are brought into contact therewith, which catalyst comprises: (A) a catalyst component A comprising (c) ceria or (d) praseodymium oxide or (e) an oxide and/or a composite oxide of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; (B) a catalyst component B comprising (d) a noble metal catalyst component selected from the group consisting of platinum, rhodium, palladium and oxides thereof and (e) a carrier; and (C) a catalyst component C comprising (f) a solid acid, and (g) a solid acid supporting an oxide of at least one element selected from the group consisting of vanadium, tungsten, molybdenum, copper, iron, cobalt, nickel and manganese.