Abstract: The invention provides a catalyst for catalytically removing three components, which are carbon monoxide, hydrocarbons and nitrogen oxides, from combustion exhaust gas generated by combusting fuel at around the stoichiometric air to fuel ratio. The catalyst includes: (A) a first catalyst component including at least rhodium, platinum, or palladium in a content of 0.01 to 0.5% by weight; and (B) a second catalyst component, which is the remainder, including a composite oxide or a mixed oxide including (a) at least zirconium oxide or titanium oxide, and (b) an oxide of at least praseodymium, yttrium, neodymium, tungsten, niobium, silicon, or aluminum, wherein the content of the oxide (a) in the composite oxide or the mixed oxide is in a range of 70 to 95% by weight. The invention further provides a two-layer catalyst that includes a surface catalyst layer containing the above-mentioned catalyst.

Abstract: The invention provides a catalyst for catalytically removing three components which are carbon monoxide, hydrocarbons and nitrogen oxides from combustion exhaust gas generated by combusting fuel in the neighborhood of the stoichiometric air to fuel ratio by bringing the combustion exhaust gas into contact therewith, the catalyst comprising: (A) a first catalyst component comprising at least one member selected from rhodium, platinum, and palladium in a content of 0.01 to 0.5% by weight; and (B) a second catalyst component, which is the remainder, comprising a composite oxide or a mixed oxide comprising (a) at least one oxide selected from zirconium oxide and titanium oxide, and (b) an oxide of at least one element selected from praseodymium, yttrium, neodymium, tungsten, niobium, silicon, and aluminum, wherein the content of the oxide (a) in the composite oxide or the mixed oxide is in a range of 70 to 95% by weight.

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: 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 catalytic direct decomposition 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 first catalyst component comprising at least one metal selected from the group consisting of rhodium and palladium supported on zeolite; (B) a second catalyst component comprising at least one selected from the group consisting of (a) ceria, (b) praseodymium oxide, and (c) a mixture and/or a composite oxide of oxides of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; and (C) a third catalyst component comprising (a) at least one selected from the group consisting of platinum, rhodium, palladium and oxides thereof, and (b) a carrier.

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: 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 structure for catalytic reduction of nitrogen oxides in exhaust gases by supplying and subjecting fuel to combustion with periodic rich/lean excursions and contacting the resulting exhaust gases with the catalyst structure, wherein the catalyst structure comprises, on an inactive substrate: (A) an outer catalyst layer comprising an outer layer catalyst component wherein the outer layer catalyst component comprises a first catalyst component comprising a mixture or a composite oxide (except mixtures or composite oxides of cerium oxides and zirconium oxides) of (a) ceria and (b) at least one oxide of at least one element selected from zirconium, gadolinium, terbium, samarium and lanthanum, and a second catalyst component comprising (c) at least one catalyst component selected from rhodium, palladium and their oxides, and (B) an inner catalyst layer comprising an inner layer catalyst component wherein the inner layer catalyst component comprises (a) at least one catalyst co

Abstract: The invention provides a catalyst for catalytic direct decomposition 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 first catalyst component comprising at least one metal selected from the group consisting of rhodium and palladium supported on zeolite; (B) a second catalyst component comprising at least one selected from the group consisting of (a) ceria, (b) praseodymium oxide, and (c) a mixture and/or a composite oxide of oxides of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; and (C) a third catalyst component comprising (a) at least one selected from the group consisting of platinum, rhodium, palladium and oxides thereof, and (b) a carrier.

Abstract: A NOx purging system using a direct reduction type NOx catalyst, wherein sulfur is purged while avoiding the occurrence of secondary sulfur poisoning, taking advantage of capability of recovery from deterioration caused by sulfur poisoning at exhaust gas temperature exhibited at normal operating zone, so that the influence of sulfur poisoning can be eliminated and NOx is efficiently purged; and a method of reactivating deteriorated catalyst therein. In particular, a NOx purging system (10) comprising exhaust gas passage (2) and, arranged therein, direct reduction type NOx catalyst (3), which NOx purging system (10) is fitted with first sulfur purge control means (222) for performing such first sulfur purge operation that when exhaust gas temperature (Tg) becomes higher than given set temperature (T1) during normal operation, not only is the oxygen concentration of exhaust gas decreased but also the exhaust temperature (Tg) is raised to not below sulfur purge temperature (Tr).

Abstract: The invention provides a method for catalytic decomposition of nitrogen oxides using periodic rich/lean excursions with a high durability even in the presence of oxygen, sulfur oxides and water and at high reaction temperatures and contacting the resulting exhaust gases with a double-layered catalyst, which is composed of an outer catalyst layer for reducing nitrogen oxides and an inner catalyst layer for the removal of CO, hydrocarbons and nitrogen oxides during rich/lean excursions. The outer catalyst layer contains a first compound, selected from cerium oxide, praseodymium oxide and mixtures of oxides selected from cerium oxide, zirconium oxide, praseodymium oxide, neodymium oxide, gadolinium oxide and lanthanum oxide, and the inner catalyst layer contains a second compound selected from rhodium, platinum, palladium, rhodium oxide, platinum oxide, palladium oxide and mixtures thereof, and a support.

Abstract: The invention provides a catalyst structure for catalytic reduction of nitrogen oxides in exhaust gases by supplying and subjecting fuel to combustion with periodic rich/lean excursions and contacting the resulting exhaust gases with the catalyst structure, wherein the catalyst structure comprises, on an inactive substrate:

Abstract: The invention provides a catalyst for catalytic reduction of nitrogen oxides which uses a hydrocarbon or an oxygen-containing organic compound as a reducing agent, which comprises silver aluminate supported on a solid acid carrier material. The invention also provides a catalyst which comprises silver aluminate and at least one transition element selected from the group consisting of W, Mo and V, each supported on a solid acid carrier material. The invention further provides a method for producing such catalysts and a method for catalytic reduction of nitrogen oxides by use of such catalysts as above mentioned.

Abstract: A process for removing nitrogen oxide from exhaust is disclosed, comprising contacting exhaust containing nitrogen oxide with an alumina catalyst which contains not more than 0.5% by weight of an alkali metal and/or an alkaline earth metal and has a total pore volume of from 0.48 to 1.2 cm.sup.3 .multidot.g.sup.-1 with 0.26 to 0.6 cm.sup.3 .multidot.g.sup.-1 of the total pore volume being formed of pores of not greater than 80 .ANG. or has a volume of pores formed of pores of not greater than 60 .ANG. of from 0.06 to 0.2 cm.sup.3 .multidot.g.sup.-l and which may have supported thereon tin in an oxidative atmosphere containing excess oxygen in the presence of a hydrocarbon or an oxygen-containing organic compound.

Abstract: A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon and/or a oxygen-containing organic compound as a reducing agent is disclosed, which comprises a cerium oxide supported on a solid acid carrier.Also, a catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon and/or an oxygen-containing organic compound as a reducing agent is disclosed, which comprises:(a) at least one element selected from the elements of Group Ib, Group IIa, Group IIb, Group IIIa, Group IIIb, Group IVa, Group IVb, Group Va, Group VIa, Group VIIa, and Group VIII in the Periodic Table (hereinafter referred to as the elements belonging to group (a)); and(b) a cerium oxide, supported on a solid acid carrier.

Abstract: A novel catalyst for catalytic reduction of nitrogen oxide using a hydrocarbon as a reducing agent is provided, which comprises (a) at least an element of the platinum group selected from the group consisting of platinum, iridium, rhodium and ruthenium and (b) gold, and which may further comprises (c) at least a metallic oxide selected from the group consisting of cerium oxide, lanthanum oxide, neodymium oxide, germanium oxide and gallium oxide.