REACTIVITY OF ZEOLITE HYDROXY-GROUPS TOWARD SIGMA-DONOR BASES - H-D EXCHANGE WITH 3-METHYLPENTANE

The H-D exchange of deuteriated Y zeolites, silica-alumina and gamma-a lumina with 3-methylpentane has been studied by IR spectroscopy. At 37 3 K exchange ocurred only in the zeolites. Silica-alumina required hig her temperatures (523-623 K) and exchange did not occur in 7-alumina i n the range of temperature studied. Ultrastable Y zeolite with non-fra mework alumina (NFA), showed a higher reactivity for H-D exchange and hexane cracking than Y zeolite dealuminated by (NH4)2SiF6. These findi ngs were explained by the difference in acid strength between the zeol ites, probably due to the presence of NFA as proposed in the literatur e, and stress the dependence of H-D exchange on acid strength. The IR study of H-D exchange between 3-methylpentane and Y zeolites having py ridine pre-adsorbed, neutralizing some of the hydroxy groups, showed t hat the high-frequency (hf) hydroxy group is responsible for the excha nge. The low-frequency (lf) and NFA hydroxy groups appear to exchange via hydrogen bridges with the hf hydroxy group, rather than by direct interaction with the hydrocarbon. The H-D exchange between solid acids and alkanes could be a qualitative test for acid strength, since only very strong acids would attack sigma bonds.