Hydrocarbon Desorption Characteristics of Metal-impregnated Zeolite and Its Evaluation in Vehicle Test

Abstract

For the purpose of heightening hydrocarbon desorption temperature for hydrocarbon adsorption-combustion catalyst, we researched about some kinds of zeolites and of hydrocarbon adsorption elements. The hydrocarbon desorption temperature for 5 type of zeolites were measured by temperature programmed desorption (TPD) with model gas which simulated engine start exhaust one. The TPD measurement showed that the beta zeolite had that the highest hydrocarbon desorption temperature and its amounts was largest among all zeolites evaluated in this study. Ag, Mg, Ni, Co, Cu, Ce and Sr addition to beta zeolite increased the toluene desorption temperature as much as 170-320°C. On the other hand, among these added elements, only Ag increased the pentane desorption temperature by 90°C. The chemical states of Ag was measured with an ultra violet visible spectrophotometer (UV-vis). UV-vis suggested that Ag+ and Ag0 (metal) increased the desorption temperature of paraffin and aromatics, respectively. After the endurance test by being exposed to an air excessive gas and a fuel excessive gas alternately at 800°C or 850°C for the catalysts, the desorption temperature of the hydrocarbon, especially of paraffin lowered. These phenomena were thought to be caused by the change of chemical state for Ag+ which existed besides the ion exchange site to Agxn+ (cluster) or Ag0 and by the sintering of Ag. The hydrocarbon desorption temperature obtained in the vehicle test was the same as the temperature predicted from the chemical state of Ag and the composition of the exhaust gas.