Dispersion-driven Lewis acidity of Cu–SiO2 catalysts

Abstract

The catalytic activity of copper nanoparticles is known to be closely related to their redox behavior. However, in supported Cu-based catalysts, the interface between the metallic nanoparticles and the support can introduce catalytic properties that are instead associated with acidity. While this phenomenon has been reported in supports that are prone to form strong metal-support interactions (SMSI), such as titania, it remains less evident in covalent solids, like silica. In this study, we compare copper-silica catalysts in both their oxidized and reduced forms, synthesized via chemisorption hydrolysis, aerosol-assisted sol–gel, and incipient wetness impregnation, focusing on their structural-textural properties and acidity levels. Experimental results show that Lewis acidity is strongly related to the dispersion of the active phase. Acidic active sites effectively promote the acid-catalyzed styrene epoxide ring alcoholysis at low temperatures (60 °C) with selectivity exceeding 90%. They are also responsible for the acid-catalyzed formation of carbonaceous deposits under a gaseous ethylene stream at high temperatures (300 °C). The nature of this acidity is the basis for the rational design of active and stable Cu-based catalysts.