| abstract |
This invention provides a β-type zeolite for an SCR catalyst that can overcome drawbacks of conventional SCR catalysts that the level of low-temperature NOx reduction properties after hydrothermal durability providing treatment is low, particularly at a temperature of 300ºC or below, and SCR catalysts using ammonia as a reducing agent have a problem of the discharge of a large amount of irritant and toxic ammonia gas into exhaust gas. A high level of low-temperature NOx reducing properties after hydrothermal durability providing treatment and a low level of discharge of irritating ammonia into exhaust gas can be realized in an SCR catalyst using a β-type zeolite for an SCR catalyst having a SiO2/Al2O3 molar ratio of not less than 20 and less than 40, an SEM particle diameter of not less than 0.35 μm, a half-value width (FWHM) of less than 0.30º in an X-ray crystal analysis (302) face, and an NH3 adsorption amount of not less than 1 mmol/g, or in an SCR catalyst using a β-type zeolite for an SCR catalyst having the above properties and further having an NH3 adsorption after hydrothermal durability providing treatment of not less than 0.4 mmol/g. |