Markedly improved performance of oxide-supported catalysts in hot basic water by three facile ways in synergy

Abstract

Use oxide-supported catalyst in green solvent, hot water : Au is anchored on oxide via Au┄O-M interaction (M = Fe, Ti, etc). Basic aqueous catalytic system may destruct a part of O M bonds into oxygen vacancies and weaken Au/support interaction, causing leaching and aggregation of Au. Three simple methods synergistically improve reusability of catalyst. • Three facile ways synergistically improve catalyst reusability in green solvent, water. • They raise support stability and Au/support interaction to reduce leaching and aggregation of Au. • Nano supports interact with Au more strongly, and are more stable in hot basic water. • Nano TiO 2 is more stable due to the stronger surface Ti O bond, in line with BOLS theory. Obtaining reusable catalysts and using water as a green solvent still remain huge challenges. Various oxides are frequently used as the support, however, the aqueous catalytic systems, particularly in hot basic water, may decrease their stability and thus cause leaching or aggregation of the supported metal nanoparticles (NPs). In this work, three very simple methods in catalyst preparation are demonstrated to greatly improve the reusability of oxide-supported catalysts in 100 °C basic water, by systematically studying a series of oxides as well as carbons as support of gold (Au) NPs and employing Suzuki-Miyaura cross-coupling (SMCC) reaction as a probe. These methods are prerequisites for obtaining both excellent activity and recyclability. Absence of any of them will badly improve leaching or aggregation of Au NPs. The reasons for the synergistically improved reusability are also elucidated in details. Though it’s extremely hard to thoroughly overcome leaching in hot water, this work achieves the application of Au/oxide to SMCC reaction in water with higher utilization efficiency of Au than some reported work in organic solvent or with other supports. The present work can serve as supplementary strategies to assist in designing high-performance oxide-supported catalysts for varieties of similar aqueous systems.