| 摘要 |
<p>PROBLEM TO BE SOLVED: To purify NOx at good efficiency in a wide temperature region by supplying a NOx reducing agent into exhaust emission flowing into an exhaust emission purifying catalyst containing zeolite and rhodium(Rh) when the temperature of exhaust emission is in the NOx adsorption temperature range of zeolite. SOLUTION: An exhaust emission purifying catalyst contains zeolite in a carrier to carry Rh. Rh has a catalytic action of reducing NOx by a NOx reducing agent. When the exhaust emission temperature is higher than the NOx adsorption temperature, NOx adsorbed to zeolite is desorbed from zeolite. At this time, the temperature is in the range of high catalytic activity of Rh, so that desorbed NOx is reduced on Rh to be purified into N2. Accordingly, NOx adsorption at low temperature is performed by zeolite, and NOx reduction at high temperature is performed by Rh. Accordingly, based on an exhaust emission temperature, it is determined whether the temperature is in the NOx adsorption temperature range of zeolite or not, and only when it is within he range, an NOx reducing agent is supplied, whereby the NOx reducing agent is effectively utilized and exhaust emission can be purified efficiently.</p> |
