| abstract |
An SCR catalyst using a β-zeolite in which the molar ratio of SiO 2 /Al 2 O 3 is from 20 to less than 40, the particle diameter determined by SEM is 0.35 μm or more, the full width at half maximum (FWHM) of the X-ray diffraction peak for (302) is less than 0.30°, and the amount of adsorbed NH 3 is 1 mmol/g or more, or has an amount of adsorbed NH 3 following hydrothermal aging of 0.4 mmol/g or more, demonstrates high catalytic activity for NOx reduction at low temperatures following hydrothermal aging while also demonstrating a low level of discharge of irritating ammonia in exhaust gas. |