The effect of high‐temperature treatment on the catalytic activity and selectivity of two HZSM5 samples has been investigated by using propane activation as the test reaction. The samples have been characterized by using X‐ray powder diffraction, nitrogen adsorption, FTIR spectroscopy, and ammonia temperature‐programmed desorption (TPD). Before high‐temperature treatment, the samples have activation energies and selectivity toward propane cracking versus dehydrogenation comparable with similar samples reported in the literature. After high‐temperature treatment (825 °C in N2), the sample’s microporous and crystalline structure remains nearly intact, but a clear decrease in the number of Brønsted‐acid sites is detected by using FTIR and ammonia TPD. Despite the decrease (≈70 %), the rate of reaction is about the same before and after heating. The selectivity toward dehydrogenation, however, increases by at least a factor of 2, whereas the activation energy for dehydrogenation decreases considerably. This is evidence that new catalytic sites are formed upon dehydroxylation. By using naphthalene as a probe molecule, it is shown that the new sites have the ability to form stable radical cations out of the neutral naphthalene, which suggests that the new sites activate propane by a redox mechanism. The kinetic isotope effect on the rate of dehydrogenation is also consistent with a redox process. The effect of heating in an oxygen atmosphere at lower temperatures was also investigated and only minor effects on reaction rates and selectivity were observed. Naphthalene adsorption experiments on oxygen‐treated samples, however, produce more radical cations than on the samples treated at high temperatures, a result that does not correlate with the dehydrogenation activity of oxygen‐treated samples.

In situ CW-EPR, diffuse reflectance UV-visible spectroscopy and Raman scattering were used to monitor the spontaneous incorporation of trans-stilbene (t-St, C 14 H 12 ) in the medium pore H 2.2 -GaZSM-5 zeolites [H 2.2 (GaO 2 ) 2.2 (SiO 2 ) 93.8 ] by direct exposure under dry and inert atmosphere of solid t-St to dehydrated porous material without any solvent. The sorption of t-St with relatively low ionization potential (7.65 eV) occurs in Brønsted acidic H 2.2 -GaZSM-5 zeolites according to a complex and slow reaction sequence. First, charge separation occurs and t-St •+ @H 2.2 -GaZSM-5 •radical pair is created, while long-lived t-St@H 2.2 GaZSM-5 •-•+ electron-hole pair is formed through hole transfer. The analysis of the DRUVv spectra set recorded during the t-St sorption course shows the respective concentrations of all transient species as a function of time. In particular, note that system reorganization is observed through a second type of electron-hole pair. The broad and strong bands observed in the near-IR regions over extended periods of time are tentatively assigned to the electron and/or hole spectral signatures in slightly different environments. Applying pulsed X-band EPR techniques, we were able to reveal the structural surrounding of the unpaired electrons of chargeseparated states through the proper assignment of electron couplings with a large number of nuclei such as 1 H, 29 Si, 69 Ga, and 71 Ga using the two-dimensional hyperfine-sublevel correlation experiment (2D-HYSCORE). The distance measurements deduced from dipolar coupling experiments provide a unique picture of the long distance distribution of unpaired electrons generated by spontaneous ionization of t-St upon incorporation within H 2.2 -GaZSM-5 zeolite. This result demonstrates that a large fraction of the unpaired electrons are ejected away from the initial site of ionization and that this compartmentalization plus the created electrostatic field hinder dramatically the propensity of charge recombination. The results for H-GaZSM-5 are compared to similar experiments conducted on H-AlZSM-5 zeolites.