“…The mechanism of transformation of NH4Y is well established by a variety of experimental methods.  The deamination of NH4Y occurs around 300°and the dehydroxylation occurs around 500°. Turkevich and Ono8'27 found that the catalytic activities for cracking of cumene and isomerization of xylene fall sharply when the calcination temperature exceeds 500°, and attributed the activity change to the loss of Br</>nsted sites (A) by dehydroxylation.…”
Publication costs assisted by the Tokyo Institute of Technology Formation of SO2-radicals over various zeolites and alumina has been confirmed using an esr technique.In the case of NH4Y, the number of radicals is maximum at the adsorption temperature of 200°, and two types of SO2-radicals are observed. One gives an esr signal with g) = 2.008 and gj_ = 2.002, is unstable over 300°, undergoes a collisional broadening in the presence of oxygen at room temperature, and reacts with oxygen at 200°. The other gives an esr signal with g|| = 2.010 and g± = 2.002, is stable up to 500°, and does not interact with oxygen. It is concluded that the adsorption sites for the former are located in the supercage and that those for the latter are located in the sodalite unit. The effect of the calcination temperature on radical formation indicates that adsorption sites for SO2-radicals are formed as a result of deamination and dehydroxylation of NH4Y. The presence of preadsorbed SO2-radicals enhances the formation of O2-radicals on decationated zeolites.
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