Enhancing Multiphase Reactions by Boosting Local Gas Concentration with Ultrafine Bubbles

Abstract

Abstract Gas–liquid phase reactions have proven invaluable for molecular transformations in laboratory and industrial applications. However, despite their advantages, the high pressure and vigorous agitation that are required to increase the dissolved gas concentration hinder their possible applications. Application of fine bubbles (FBs), which have a diameter smaller than 100 µm, 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.