Modification of Salt‐Templated Carbon Surface Chemistry for Efficient Oxidation of Glucose with Supported Gold Catalysts

Abstract

Gold nanoparticles dispersed on high‐surface‐area carbon materials were investigated as heterogeneous catalysts for the selective oxidation of d‐glucose to d‐gluconic acid in aqueous solution with molecular oxygen. Salt‐templated porous carbon supports were obtained from different precursors with and without nitrogen and treated under air or hydrogen atmosphere to functionalize the surface with nitrogen, oxygen, or hydrogen. The influence of the surface atomic structure of the carbonaceous supports with similar pore structure on the size and catalytic properties of the metallic nanoparticles was studied at gold nanoparticle loadings of 0.4–0.7 wt %. The functionalisation significantly influences the surface polarity of the support materials and the strength of the interaction with the gold nanoparticles. The surface polarity influences the structure and properties of the catalysts because both the gold deposition and the glucose oxidation reaction take place in the aqueous phase. Rather hydrophilic supports are obtained by doping with oxygen and nitrogen and lead to large gold nanoparticles with low catalytic activity. In contrast, the rather hydrophobic as‐made and hydrogen‐treated supports provide higher catalytic activity (metal time yield up to 1.5 molGlucose molAu−1 s−1) resulting from their smaller gold particles of 3–5 nm in diameter.

Gold Catalysts for the Selective Oxidation of Biomass‐Derived Products

“…Interestingly, Megías-Sayago and co-workers, found that the TOF of Au nanoparticles on activated carbon increased increasing the average particle diameter from 4 nm to 23 nm. [52] Benkó and co-workers found a similar trend when comparing the activity of Au nanoparticles in a range of 5-13 nm supported on TiO 2 , SiO 2 and CeO 2 , although they ascribed the enhanced activity of the Au/SiO 2 catalyst to metal-support interactions. [53] Support effects were hypothesised by Megías-Sayago et al comparing Au particles in a 3-5 nm range supported on different metal oxides.…”

“…Using Au nanoparticles of different size in a 3–6 nm range, the catalytic activity was found to be inversely proportional to the particles diameter (Scheme ). Later studies on Au nanoparticles supported on different types of carbons confirmed this trend ,. Contrasting results were however reported by several authors.…”

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

“…Before the deposition of active species, CMK‐3 has been treated under a reducing atmosphere, to remove surface functional groups and ensure hydrophobic surface structure. This is an effective strategy for stabilization of small catalytically active AuNPs and avoiding their growth upon deposition [20] . The Au−C catalyst was obtained by deposition of 1 wt% of AuNPs on the porous surface of the carbon support.…”

Controlling pore size and pore functionality in sp2-conjugated microporous materials by precursor chemistry and salt templating

“…This templating approach is one strategy for the introduction of porosity. [11][12][13] It is particularly attractive as it only demands abundant and potentially reusable, simple inorganic salts as pore-forming agents. No amphiphilic molecules or nanostructured inorganic materials are required and the salts can be removed by simply washing with water or by evaporation during carbonization.…”