EXHAUST GAS PURIFYING CATALYST

摘要

Disclosed is an exhaust gas purifying catalyst for oxidizing and purifying diesel exhaust gases that is improved in utilization efficiency by optimizing the thickness of the catalyst coating layer thereof. The suitable precious-metal amount (A) is defined as the amount of catalytic precious metal at the point where the increase in exhaust gas purification rate sharply peaks out with respect to the increase in the amount of catalytic precious metal per unit volume of the catalyst; the suitable carrying density (B) is defined as the catalyst carrying density, which is the weight of the catalytic precious metal per unit weight of a catalyst carrier, at the point where the increase in the particle size of the catalytic precious metal caused by heating sharply rises with respect to the increase in the catalyst carrying density; the minimum thickness is defined as the catalyst coating thickness (Y1) found from the catalyst coating amount (X1), which is the ratio (A/B) between said suitable precious-metal amount (A) and said suitable carrying density (B), by employing the monotonically increasing relational expression between the catalyst coating amount (X) per unit volume of the catalyst and the catalyst coating thickness (Y); and the maximum thickness is defined as the catalyst coating thickness at the point where the exhaust gas purification performance sharply drops with respect to the increase in the catalyst coating thickness. The exhaust gas purifying catalyst comprises a catalyst coating layer having a thickness within the range of from said minimum thickness to said maximum thickness.