Silver species reduction upon exposure of Ag/Al2O3 catalyst to gaseous ethanol: An in situ Quick-XANES study

The evolution of supported silver species of a pre-calcined Ag/Al2O3 catalyst was monitored upon thermal treatment under an air flow enriched with 3000 ppm of ethanol (EtOH) using transmission electron microscopy and UV–visible and X-ray absorption spectroscopies. A special focus is put on the application of in situ Quick-XAS that permits to acquire high quality spectra at the Ag K-edge with a good time resolution (30 s), thus informing in real time on the transformations of the silver species. While the reduction of silver under Air/EtOH flow is shown to possibly occur at room temperature, the process is strongly accelerated by heating, most of the silver being indeed reduced at ca. 78 °C, a temperature which corresponds to the ethanol boiling point. The possible impact of this silver sensitivity on the behavior of silver–alumina catalysts in reactions such as the selective catalytic reduction (SCR) of NOx in presence of ethanol is addressed.