EXHAUST GAS CLEANING CATALYST AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce an exhaust gas cleaning catalyst having high NOx absorbing properties in an oxygen excessive region, also good in the reactivity with discharged NOx and reducing substances such as HC and CO and excellent in NOx cleaning capacity and durability. SOLUTION: An exhaust gas cleaning catalyst obtained by coating a refractory inorg. carrier with a catalyst layer containing a noble metal consisting of platinum and palladium and/or rhodium and an NOx absorbing material. Platinum is present at a distance sufficient to receive NO2 from the NOx absorbing material so as to satisfy M(NO3)2→2NO2+3/2O2+MO (wherein M is an NOx adsorbing material). Platinum becomes high in concn. as approaching the surface of the catalyst layer and 10-100% of the total amt. of platinum is contained in the catalyst layer up to a depth of 0.1 mm from the surface thereof. The catalyst layer containing the NOx absorbing material and the noble metal is applied to the refractory inorg. carrier by an impregnation method to produce the exhaust gas cleaning catalyst.