Nature of HCl oxidation Au anomalies and activation of non-carbon-material-supported Au catalyst

Supported cationic gold (Au) has been recognized as an active site of acetylene hydrochlorination for dec-ades; however, it remains ambiguous why its loading on carbon-based materials is active but that on metal oxides (e.g., titania, TiO2) is virtually inactive. For the inactive Au/TiO2 catalyst, the Au(I)-Au(III) redox couple cannot be constructed in the presence of oxidizing gas (NO, N2O, and NO2), which is ther-mally desorbed from the catalyst synthesis when aqua regia is used. Surprisingly, the inactive Au/TiO2 can be activated when it is impregnated with trichloromethane, CHCl3, which releases the radical (Cl) to trigger the Au(I)-Au(III) redox couple. Once Cl-center dot radicals are consumed, the reaction will be terminated, although a large amount of supported cationic Au remains. The terminated Au/TiO2 catalyst can be reac-tivated by adding Cl-center dot again. In contrast to the carbon-supported cationic Au system, the inability to build Au(I)-Au(III) redox couples is the dominant reason for the inactivity of metal-oxide-supported Au cata-lysts and provides a new perspective on activating metal-oxide-supported metal-based hydrochlorina-tion catalysts. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

Supported cationic gold on carbon-based materials is active in acetylene hydrochlorination, while on metal oxides it is virtually inactive. The inactive Au/TiO2 catalyst can be activated by impregnating it with trichloromethane to release Cl radicals and trigger the Au(I)-Au(III) redox couple.