A combined use of DFT periodic calculations and spectroscopic studies (IR and solid-state NMR) shows that a γ-alumina treated at 500°C under high vacuum contains surface defects, which are very reactive toward H 2 or CH4. The reaction of H2 on defect sites occurs at low temperature (ca. 25°C) on two types of Al atoms of low coordination numbers, Alm or AlIV, to give Al IV-H and Alv-H, respectively. The amount of defects as titrated by H2 at 25 and 150°C is 0.043 and 0.069 site/nm 2, respectively, in comparison with 4 OH/nm2). In contrast, CH4 reacts selectively at 100-150°C on the most reactive AlIII sites to form the corresponding AlIV- CH3 (0.030 site/nm2). The difference of reactivity of H2 and CH4 is fully consistent with calculations (reaction and activitation energy, ΔE and ΔE‡).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry