Reactions of Electrons on the Surface of γ-Al_2O_3. A Pulse Radiolytic Study with 0.4 MeV Electrons

摘要

Radiolysis of γ-alumina produces electrons, e~-, and positive holes, h~+. These species rapidly migrate tot he surface to produce products of surface adsorbed compounds. The electrons are also trapped by surface OH groups giving rise to short-lived (<10 μs) trapped electrons, e_t~-. Heating the γ-Al_2O_3 produces Lewis acid sites and decreases the OH content of the surface. Such material produces much lower yields of trapped electrons, as e~- then reacts predominantly with the Lewis acid sites. Hydrogen gas is produced on radiolysis of γ-Al_2O_3 via H atom formation from e~-. The H atoms may recombine, producing H_2, or react with surface adsorbed materials (e.g., pyrene) to produce H atom adducts. The basic radiation chemistry is similar to that observed in zeolites (but not SiO_2), where ionization predominates. These studies illustrate for the first time the production of electrons in a γ-Al_2O_3 surface and the consequent two-dimensional kinetics of these species on the surface.