Detection and Quantitative Measurements of Four Kinds of OH in HY Zeolite

Acidity of in situ prepared HNaY zeolite was studied by a method of infrared mass spectrometry/temperature-programmed desorption (IRMS-TPD) of ammonia. Two kinds of energetically different acid sites were detected in the TPD experiment. Adsorption of ammonia on the HNaY revealed the IR bending vibration bands at ca. 1430 and 1665 cm-1, and these bands corresponded to ammonia molecules desorbed at high and low temperatures, respectively. By using the IR-TPD, four kinds of OH bands were detected, although the evacuated HY showed usually only two OH bands. Two OHs in the super cage and two in the sodalite cage and hexagonal prism were identified. From the comparison of IR-TPD of adsorbed ammonia and OH, it was found that the NH4 + cation was formed on three of four OHs located in super and sodalite cages. An interaction of ammonia on the OH located in the hexagonal prism was, however, different. By using a curve fitting method, the number of these OHs as the acid site was quantified, and the strength was measured on the basis of the theoretical equation on in situ prepared HNaY with a 96% proton exchange degree. A dependence of the OH concentration on the exchange degree 14−96% was measured. Extinction coefficients of OH stretching vibrations were also determined.