Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
The application of the technique of angular correlation of the annihilation radiation (ACAR) from positron-electron pairs for investigating Bronsted acid sites in zeolytic catalysts was initially introduced by the authors with remarkable success. As incident positrons enter polycrystalline zeolites, a portion of the incident positrons would diffuse through the bulk and emerge on the internal surfaces and form with electrons there hydrogen-like positronium atoms (Ps). The Ps atoms will eventually annihilate also and generate an ACAR spectrum that is distinctively narrower than the one from the bulk.
In the presence of Bronsted acid sites, the Ps atom population would be reduced through oxidation by protons, resulting in alteration of the ACAR spectrum which is gauged by using a lineshape parameter S. In this report, results from ACAR measurements for based-adsorbed NaHY zeolites will be presented and discussed in light of acidic stregth and effect of molecular size.
Acknowledgement: This project was partially supported by grants from NSF and Taiwan National Science Council.