Development of hydrocarbon adsorbents, oxygen storage materials for three-way catalysts and NOx storage-reduction catalyst

Hydrocarbon adsorbents, three-way catalysts and NOx storage-reduction catalysts for application in gasoline engines have been studied at Toyota in order to meet more stringent environmental regulations. The hydrocarbon adsorption capacity of zeolites has been studied. Hydrocarbon adsorption increased with decreasing aluminum content. Zeolites with a pore size approximately 0.1 nm greater than the diameter of the hydrocarbon molecules showed the best performance. Two zeolites with different pore size were mixed, and this strategy succeeded in adsorbing hydrocarbons of carbon number 3 and above. Silver (Ag) ion-exchanged zeolite was used to increase the adsorption of exhaust gas hydrocarbons, including those of carbon number 2. To optimize the performance of three-way catalysts, another development project focused on the heat resistance of CeO2-ZrO2 solid solutions (CZ) with oxygen storage capacity (OSC). We devised a new method of inhibiting the coagulation of the primary CZ particles by placing diffusion barrier layers made of alumina among the primary CZ particles. This material is called "ACZ". The OSC and the light-off temperature of the ACZ-added catalyst are improved. For the improvement of NOx storage-reduction catalysts (NSR catalysts), we focused on the performance deterioration at high temperature via sulfur-poisoning and thermal degradation. A new zirconia-titania complex metal oxide was developed which improves the high-temperature performance and to promotes desorption of sulfur from the supports after aging. (C) 2004 Elsevier B.V. All rights reserved.