Immobilization of Gold‐on‐Carbon Catalysts Onto Perfluorocarbon Emulsion Droplets to Promote Oxygen Delivery in Aqueous Phase _D‐Glucose Oxidation

Abstract

The catalytic activity of metal nanoparticles (NPs) supported on porous supports can be controlled by various factors, such as NPs size, shape, or dispersivity, as well as their interaction with the support or the properties of the support material itself. However, these intrinsic properties are not solely responsible for the catalytic behavior of the overall reaction system, as the local environment and surface coverage of the catalyst with reactants, products, intermediates and other invloved species often play a crucial role in catalytic processes as well. Their contribution can be particularly critical in liquid‐phase reactions with gaseous reactants that often suffer from low solubiltiy. One example is D‐glucose oxidation with molecular oxygen over gold nanoparticles supported on porous carbons. The possibility to promote oxygen delivery in such aqueous phase oxidation reactions via the immobilization of heterogenous catalysts onto the interface of perfluorocarbon emulsion droplets is reported here. Gold‐on‐carbon catalyst particles can stabilize perfluorocarbon droplets in the aqueous phase and the local concentration of the oxidant in the surroundings of the gold nanoparticles accelerates the rate‐limiting step of the reaction. Consequently, the reaction rate of a system with the optimal volume fraction of fluorocarbon is higher than a reference emulsion system without fluorocarbon, and the effect is observed even without additional oxygen supply.

Synthesis of Polymer Janus Particles with Tunable Wettability Profiles as Potent Solid Surfactants to Promote Gas Delivery in Aqueous Reaction Media

“…Next, we leveraged the potential of as-synthesized Janus particles (Figure a, interfacial contact angle of θ = 61°) that result in low interfacial contact angles to act as solid surfactants for the stabilization of air bubbles in water and tested their ability to increase the gas content and thus promote the delivery of oxygen (Figure S15) inside a liquid-phase oxidation reaction medium. An increase in the local concentrations of gaseous reactants in proximity to the dispersed solid catalysts has been previously associated with an enhanced catalytic performance. , We opted for an aqueous phase oxidation reaction of d -glucose to gluconic acid because, apart from being a relevant industrial reaction for producing higher value-added chemicals from biomass, it also presents itself as a defined and well-investigated reaction with high selectivity toward a single product, mild reaction conditions, and simple access to monitor the reaction rate (Figure a). − In our experiments, we used unsupported gold nanoparticles as catalysts for the aqueous phase d -glucose oxidation that were added as aqueous dispersion (53 mg L –1 ) to an d -glucose solution (0.4 M). Throughout the reaction, the pH value of the mixture was kept constant at pH = 9 via titration with a sodium hydroxide standard solution (1 M).…”

Modification of Gold Zeolitic Supports for Catalytic Oxidation of Glucose to Gluconic Acid

“…Recently, Hutchings [2] has pointed out that work on improvement of catalyst performance or designing new ones must be based on deep understanding of the reaction mechanism. In the last few years, Au NPs have been deposited on several different supports (e.g., mesoporous silica [3], metal oxides [4][5][6] and carbons [7,8]) and applied as catalysts in glucose oxidation. However, glucose oxidation carried out over gold catalysts supported on zeolites belongs to the reactions whose pathways have not been fully solved [9].…”