(379d) Green Selective Oxidation Using Heterogenous Catalytic Sonochemistry

Sonochemistry is the use of high frequency sound waves (ultrasound) to facilitate chemical reactions. It has garnered interest as a potential route for greener chemistry by creating locally intense temperatures and pressures under bulk ambient conditions. These extreme conditions are achieved by acoustically forcing bubbles in a liquid to implode (i.e., inertial cavitation). The implosion induces pyrolysis of vapour or gases trapped in the bubble, generating light and radicals beneficial for chemical reactions otherwise unachievable in the bulk. However, sonochemistry is limited by the large electrical energy required to nucleate cavitation, the low selectivity of cavitation, and the stochastic nature of cavitation. To remedy this, researchers have exploited using heterogenous catalysts to increase the radical generation rate and control selectivity. Yet, the stochasticity of cavitation require these approaches to use prolonged periods of high intensity, continuous wave irradiation to generate sufficient reaction rates. Here, we address these limitations by nanostructuring TiO₂ to function as a catalytic cavitation agent (CCA). By introducing gas bubbles to the catalyst surface, we demonstrate that cavitation can more efficiently occur at the catalyst location and with lower input energies to the sonochemical reactor. Furthermore, we modified the CCAs with AuPd nanoparticles to function as a co-catalyst that enhanced sonoreactivity. Using our approach, we demonstrate selective oxidation of benzyl alcohol to benzaldehyde as a model reaction. In summary, our findings present the key design elements for developing an effective CCA, allowing future work to explore the versatility of CCAs as a route for greener chemistries.