Support effects in iridium-catalyzed aerobic oxidation of benzyl alcohol studied by modulation-excitation attenuated total reflection IR spectroscopy

The influence of the support (Al2O3, CeO2, TiO2) in the oxidation of benzyl alcohol (BA) to benzaldehyde on Ir-based catalysts was investigated by ATR-IR spectroscopy in tandem with modulation excitation spectroscopy (ATR-IR-MES) at working conditions of the catalysts. ATR-IR-MES unveiled the dissociative adsorption of BA and the formation of adsorbed transient alkoxy species (C6H5CH2O-) to be key for high catalytic performance. These species were detected on Ir/TiO2 and Ir/Al2O3 but not on Ir/CeO2, which exhibited poor catalytic performance. On Ir/TiO2 pretreated with hydrogen at 450 degrees C about 84% of the Ir sites were blocked due to formation of a titania overlayer. However, this catalyst afforded a more than seven times higher activity than the corresponding one pretreated at 300 degrees C, where about 68% of the Ir sites were blocked. The high activity of the titania overlayer is attributed to the formation of Ti cations with oxygen vacancies caused by the hydrogen pretreatment. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

In the oxidation of benzyl alcohol to benzaldehyde on Ir-based catalysts, the influence of support materials Al2O3, CeO2, and TiO2 was studied. Among them, TiO2 exhibited high catalytic performance, while CeO2 showed poor performance. The formation of a titania overlayer after hydrogen pretreatment significantly affected the catalytic activity.