Exhaust gas-purifying composition
The present invention provides an exhaust gas purifying composition containing BEA zeolite containing phosphorus, wherein an amount of phosphorus is such that a molar ratio thereof with respect to Al in the zeolite is 0.5 or greater, and a maintaining factor R S of a specific surface area of the exhaust gas purifying composition after heating at 980° C. for 25 hours is 35% or greater. Furthermore, the present invention also provides an exhaust gas purifying composition containing phosphorus-containing zeolite, wherein an amount of phosphorus is such that a molar ratio thereof with respect to Al in the zeolite is from 0.5 to 8, and a maintaining factor R d of a crystallite diameter after heating at 980° C. for 25 hours is 50% or greater. The exhaust gas purifying composition of the present invention has excellent HC purifiability for exhaust gas purification in internal combustion engines such as gasoline engines.
1. An exhaust gas purifying composition comprising BEA zeolite containing phosphorus and zirconium, wherein
an amount of phosphorus contained in the zeolite is such that a molar ratio (P/Al) thereof with respect to Al in the zeolite is 0.5 or greater, and an amount of zirconium contained in the zeolite is such that a molar ratio (Zr/Al) thereof with respect to Al in the zeolite is 0.25 or greater, and
when (a1) A represents a specific surface area of the exhaust gas purifying composition after heating at 980° C. for 25 hours, and (a2) B represents a specific surface area of the exhaust gas purifying composition before the heating,
a maintaining factor R S of a specific surface area of the exhaust gas purifying composition represented by A/B×100(%) is 35% or greater.
2. An exhaust gas purifying composition comprising BEA zeolite containing phosphorus, wherein
an amount of phosphorus is such that a molar ratio thereof with respect to Al in the zeolite is from 0.5 to 8, and an amount of zirconium contained in the zeolite is such that a molar ratio (Zr/Al) thereof with respect to Al in the zeolite is 0.25 or greater, and
when (b1) X represents a crystallite diameter of the zeolite after heating the exhaust gas purifying composition at 980° C. for 25 hours, and (b2) Y represents a crystallite diameter of the zeolite before the heating,
X is 25 nm or less, and a maintaining factor R d of a crystallite diameter represented by X/Y×100(%) is 50% or greater.
3. The exhaust gas purifying composition according to claim 1 , wherein
an amount of phosphorus is such that a molar ratio (P/Al) thereof with respect to Al in the zeolite is from 1 to 3.
4. The exhaust gas purifying composition according to claim 2 , wherein X is 15 nm or less.
5. An exhaust gas purification method, using a composition comprising BEA zeolite containing phosphorus and zirconium, wherein,
in the composition, an amount of phosphorus contained in the zeolite is such that a molar ratio (P/Al) thereof with respect to Al in the zeolite is 0.5 or greater, and an amount of zirconium contained in the zeolite is such that a molar ratio (Zr/Al) thereof with respect to Al in the zeolite is 0.25 or greater, and
when (a1) A represents a specific surface area of the composition after heating at 980° C. for 25 hours, and (a2) B represents a specific surface area of the composition before the heating,
a maintaining factor R S of a specific surface area of the composition represented by A/B×100(%) is 35% or greater.
6. An exhaust gas purification method, using a composition comprising BEA zeolite containing phosphorus and zirconium, wherein,
in the composition, an amount of phosphorus contained in the zeolite is such that a molar ratio (P/Al) thereof with respect to Al in the zeolite is from 0.5 to 8, and an amount of zirconium contained in the zeolite is such that a molar ratio (Zr/Al) thereof with respect to Al in the zeolite is 0.25 or greater, and
when (b1) X represents a crystallite diameter of the zeolite after heating the exhaust gas purifying composition at 980° C. for 25 hours, and (b2) Y represents a crystallite diameter of the zeolite before the heating,
X is 25 nm or less, and a maintaining factor R d of a crystallite diameter represented by X/Y×100(%) is 50% or greater.
7. The exhaust gas purification method according to claim 5 , comprising removing hydrocarbon contained in exhaust gas, the exhaust gas is emitted into an exhaust passage of an internal combustion engine.
8. The exhaust gas purifying composition according to claim 1 , wherein an amount of zirconium contained in the zeolite is such that a molar ratio (Zr/Al) thereof with respect to Al in the zeolite is from 0.5 to 4.
9. The exhaust gas purifying composition according to claim 1 , wherein the zirconium contained in the zeolite is supported by the zeolite.