Chapter 14 - Electron Transfers Under Confinement in Channel-Type Zeolites

Abstract

Electron transfers following the ionization of probe molecules adsorbed in channel-type zeolites are reported as a function of the internal confinement (ferrierite—FER, zeolite socony Mobil-FIve—MFI, mordenite—MOR, beta—BEA), of the molecule type and of the charge-balancing cation. Spontaneous ionization is observed in acidic zeolites for all molecules and all zeolite morphologies. This process occurs also in nonacidic and even in Al-free MFI for molecules with low ionization potential like aromatic amines (I.P. <7eV) and for molecules with higher ionization potential in Li-, Na-exchanged zeolites when confinement is very tight (FER). In the absence of spontaneous ionization, photoexcitation is required to induce charge separation. Regardless of the initial ionization process (spontaneous or photoinduced), the electron transfers and transient species formed are identical but exhibit very different lifetimes from seconds to months. The crucial role of the internal porosity in the reactivity is demonstrated by comparing the behavior of molecules able to penetrate into the pores and molecules of the same family unable to enter due to sterical constraints.