Enhancing Multiphase Reactions by Boosting Local Gas Concentration with Ultrafine Bubbles

Gas -liquid phase reactions have proven invaluable for molecular transformations in laboratory and industrial applica-tions. However, despite their advantages, the high pressure and vigorous agitation that are required to increase the dissolved gas concentration hinder their possible applications. Applica-tion of fine bubbles (FBs), which have a diameter smaller than 100 over bar m, enables gas -involved reactions under mild conditions. In this study, we quantified and evaluated the reactivities of FBs and dissolved gases under various FB conditions. The photooxidation of sulfide using O2-FB-generated sulfoxide depends on the dissolved O2; meanwhile, H2-FB-mediated hydrogenation of alkenes with a Pd catalyst produced higher yields than expected from the dissolved H2. In a gas-liquid solid phase reaction, FBs on the metal catalyst may form a gas tunnel between neighboring FBs and increase the local gas concentration, providing higher yields. The applicability of this effect was evaluated via hydrogenation using a deactivated metal catalyst in the presence of H2-FBs, which led to recovery from catalyst poisoning. The research findings demonstrated that surface FBs play a crucial role in enhancing reactivity that involves solid phases. In addition, we executed FB-mediated hydrogenation with a poisoned catalyst to demonstrate the ability of bubbles to suppress the catalyst poisoning.