Metal sols as a useful tool for heterogeneous gold catalyst preparation: reinvestigation of a liquid phase oxidation

Gold-nanoparticle-based catalysts for the oxidative esterification of 1,4-butanediol into dimethyl succinate

The oxidation of 1,4-butanediol and butyrolactone have been investigated by using supported gold, palladium and gold-palladium nanoparticles. The products of such reactions are valuable chemical intermediates and, for example, can present a viable pathway for the sustainable production of polymers. If both gold and palladium were present, a significant synergistic effect on the selective formation of dimethyl succinate was observed. The support played a significant role in the reaction, with magnesium hydroxide leading to the highest yield of dimethyl succinate. Based on structural characterisation of the fresh and used catalysts, it was determined that small gold-palladium nanoalloys supported on a basic Mg(OH)2 support provided the best catalysts for this reaction.

Tuning the textural and surface properties of carbon xerogels to be used as supports for gold catalysts

Carbon xerogels (CXs) synthesized from resorcinol and formaldehyde under different pH conditions were investigated. Both the textural and surface properties of the CXs depend closely on the pH used in the synthesis procedure. Concerning the texture, the mesoporous surface area (Smeso) increases and the micropore volume (Vmicro) decreases as the pH increases; concerning the surface chemistry, surface oxygen functional groups were easier to be created (by O2) on CX synthesized at lower pH. Application of these CXs as support of gold catalysts was also studied. Results showed that the oxygen activated CX that was synthesized at moderate pH (i.e., pH 6.0) was the most favorable support for gold catalysts used in selective oxidation of benzyl alcohol by molecular oxygen in liquid phase, due to the adequate amounts of surface oxygen functional groups created on the surface.

Oxidation of benzyl alcohol by using gold nanoparticles supported on ceria foam

The efficacy of using cerium oxide foams as a support for Au nanoparticles and subsequent use as oxidation catalysts have been investigated. These were synthesized using L-asparagine to produce a cerium coordination polymer foam, which was calcined to give the oxide foam. Au nanoparticles were supported on the CeO(2) foams using a sol-immobilization method. The activity of the Au/foamCeO(2) for solvent-free benzyl alcohol oxidation was superior to standard Au/CeO(2) catalysts, and the activity was found to be dependent on the crystallization time of the precursor foam. A crystallization time of 4 h was found to produce the most active catalyst, which retained activity and a high selectivity to benzaldehyde (ca. 96 %) when re-used and this is related to the structure of the material. The high activity is attributed to the greater lability of surface oxygen in the support compared with commercial CeO(2) materials.

Surprisingly strong effect of stabilizer on the properties of Au nanoparticles and Pt^Au nanostructures in electrocatalysis

We show that the electrocatalytic properties of nearly monodispersed Au nanoparticles (NPs) and their derived Pt-on-Au (Pt^Au) nanostructures with similarly dispersed Pt entities are dependent on the nature of stabilizers involved in the colloidal syntheses of the Au particles. The effect of stabilizer on the activity for oxygen reduction reaction (ORR) of Au NPs significantly outweighed the Au nano-size effect and thus would raise an alert to those reported size-dependent properties of metal NPs carrying various stabilizers in earlier studies. It is also demonstrated that the stabilizer effect on the property of Au NPs can further induce changes in the catalytic properties of their carried Pt. These findings clearly suggest that a proper screening of the stabilizer in the colloidal synthesis of metal NPs would be important for innovative nanomaterials and catalysts.

Sustainable preparation of supported metal nanoparticles and their applications in catalysis

Metal nanoparticles have attracted much attention over the last decade owing to their unique properties as compared to their bulk metal equivalents, including a large surface-to-volume ratio and tunable shapes. To control the properties of nanoparticles with particular respect to shape, size and dispersity is imperative, as these will determine the activity in the desired application. Supported metal nanoparticles are widely employed in catalysis. Recent advances in controlling the shape and size of nanoparticles have opened the possibility to optimise the particle geometry for enhanced catalytic activity, providing the optimum size and surface properties for specific applications. This Review describes the state of the art with respect to the preparation and use of supported metal nanoparticles in catalysis. The main groups of such nanoparticles (noble and transition metal nanoparticles) are highlighted and future prospects are discussed.

Biomass into chemicals: aerobic oxidation of 5-hydroxymethyl-2-furfural into 2,5-furandicarboxylic acid with gold nanoparticle catalysts

5-hydroxymethyl-2-furfural is selectively converted into 2,5-furandicarboxylic acid (99 mol % yield) in water, under mild conditions (65-130 degrees C, 10 bar air) with gold nanoparticles supported on nanoparticulate ceria (Au-CeO(2)) and on titania (Au-TiO(2)); the former being more active and selective. A reaction mechanism is established and the rate-limiting step of the reaction is the alcohol oxidation of 5-hydroxymethyl-2-furancarboxylic acid into 2,5-furandicarboxylic acid. The effects of pressure, temperature, substrate-to-catalyst ratio, and amount of base are studied to find the most suitable reaction conditions. The absence of metal leaching is verified by chemical analysis of the reaction solution and by confirming that the reaction does not occur after catalyst removal by filtration in hot water. Substrate degradation is strongly diminished and the catalyst life increased by performing the reaction in two temperature steps.