日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Low-temperature activity is an important requirement for automotive catalysts. In particular, most of the tailpipe emissions occur right after the engine starts. These cold emissions can be effectively reduced by using a trap material such as zeolite for hydrocarbon (HC) adsorption. However, using zeolite in automotive catalyst is largely limited due to its low durability under hydrothermal aging conditions. In most cases, zeolites need to be placed away from large thermal loads in order to take advantage of their adsorption abilities. In general, the thermal endurance of close-coupled catalysts for gasoline powered vehicles proceeds at about 1000°C in the presence of water. Under these conditions, the zeolite structure would be decomposed by the dissociation of aluminum from the zeolite frameworks. Through this study, we show that the hydrothermal durability of zeolite can be dramatically improved by chemical modification of zeolite with zirconium phosphate. This improvement strategy works well, especially for Beta-type zeolites with low silica-alumina ratio. We also found that this modified Beta zeolite worked well as HC trap material and showed an enormous reduction of cold HC emissions with Pd/Rh three-way catalyst (TWC).In the vehicle test evaluations with the close-coupled TWC+TWC and TWC+HC trap system as aged catalysts, advantages of this HC trap catalyst in cold emissions were observed. It is found that HC emission decrease by up to 43% when compared to those from the corresponding TWC+TWC system which does not have any zeolite. In this report, we introduce the performance of this highly durable zeolite and the discussions about mechanism for generating high durability based on nuclear magnetic resonance (NMR) analyses.