ZEOLITE CHEMISTRY OF CuZSM-5 REVISITED

The recently reported interesting behavior of the EPR spin intensity as freshly prepared CuZSM-5 is dehydrated has been confirmed, and the interpretation offered in explanation has been tested by extending the data. Magnetic susceptibility and optical diffuse reflection spectroscopy have been used to show that the anomalous EPR data correspond to changes in symmetry rather than disproportionation of [CuOH]+ into Cu+ and Cu2+O- as H2O is removed, as previously suggested. Moreover, the relatively small negative Weiss constants suggest that antiferromagnetic coupling through the supposedly EPR silent conventional bridge species, [Cu2+-O2- Cu2+]2+, cannot be responsible for the relatively large changes in observed EPR spin intensity on dehydration. EPR measures selectively individual paramagnetic species and ignores those of low symmetry, while magnetic susceptibility integrates over all magnetic species in the sample. The changes in the EPR intensities were much larger than those observed by magnetic susceptibility. Furthermore, those from EPR occurred as the first H2O was removed, before any significant change in susceptibility occurred. The EPR data reflected those expected for the decrease in symmetry accompanying dehydration. Support for these views was found in the magnetic susceptibility and optical reflectance data. Evidence for CuO formation concomitant with dehydration was obtained.