β-Zeolite for SCR catalyst and method for purifying nitrogen oxides using same

摘要

An SCR catalyst using a β-zeolite in which the molar ratio of SiO₂/Al₂O₃ 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 NH₃ is 1 mmol/g or more, or has an amount of adsorbed NH₃ 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.