Catalysis and Reactivation of Ordered Mesoporous Carbon-Supported Gold Nanoparticles for the Base-Free Oxidation of Glucose to Gluconic Acid

Abstract

An ordered mesoporous carbon (CMK-3)-supported gold catalyst was prepared and used in the aerobic oxidation of glucose to gluconic acid under base-free conditions with molecular oxygen. XRD and TEM results revealed that gold nanoparticles were uniformly dispersed on the surface and in the channels of CMK-3. Catalytic tests showed that conversion remarkably increased with decreased selectivity when oxygen pressure and reaction temperature were increased. Glucose conversion to gluconic acid reached over 92% with 85% selectivity under the conditions of 383 K reaction temperature, 0.3 MPa oxygen pressure, and 2 h reaction time. Hydrogen peroxide was generated during reaction, and the relationship between hydrogen peroxide and the byproduct fructose was discussed. Low glucose/Au molar ratio minimized fructose formation. A 92% gluconic acid yield was obtained after reaction for 15 min when the molar ratio of glucose/Au was set to 100. The spent catalyst treated with an aqueous solution of NaOH at 363 K could produce glucose conversion up to 87%, which was close to the result of as-prepared catalyst and excluded the effect of alkaline residues.

Advances in Base-Free Oxidation of Bio-Based Compounds on Supported Gold Catalysts

“…The highest yield of the corresponding sugar acid was achieved at the temperature of 70 • C. Above this temperature, several other overoxidation products appeared, as a result of thermal decomposition and polymerization. A similar trend of decreased selectivity as the temperature increased was reported on Au/CeO 2 [25] and Au/CMK-3 catalysts [43] for base-free oxidation of glucose. At a relatively low temperature (namely, 70 • C), no byproduct was observed (Table 6).…”

“…It showed an excellent selectivity towards gluconic acid [6]. Puyu Qi et al [43] used an ordered mesoporous carbon (CMK-3)-supported Au catalyst in the aerobic oxidation of glucose with O2 under base-free conditions. Catalytic tests showed that the conversion remarkably increased, but the selectivity decreased when oxygen pressure and reaction temperature were increased.…”

“…The conversion could be improved by only 5% through a calcination treatment. Qi et al [43] discussed two different regeneration methods, including NaOH treatment and calcination, for an Au/CMK-3 catalyst that had gradually lost its activity upon recycling during glucose oxidation. On the basis of their results, the used catalyst treated with 50 mL of 0.1 mol/L NaOH for 30 min at 90 • C showed the best performance, with 87% conversion.…”

Electrocatalytic and Electroanalytic Investigation of Carbohydrates Oxidation on Gold-Based Nanocatalysts in Alkaline and Neutral pHs

“…13 For instance, gluconic acid from the selective glucose oxidation in a two-electron process is a mild organic acid that has received great interest in various fields such as food, pharmaceutical, and cosmetic industries. 13,22,23 Seminal investigations in electrocatalysis showed that the alkaline medium is the environment of choice for mono-and polyhydric alcohols electrooxidation. [24][25][26][27] Hence, performing selectively these reactions in order to produce chemicals of interests within a cogeneration configuration is an excellent tool to cut down the H 2 production cost.…”

Electrocatalytic Oxidation of Cellulose to Gluconate on Carbon Aerogel Supported Gold Nanoparticles Anode in Alkaline Medium

“…For the 50 nm-Au/CA anode, it obtained a high cellulose conversion; however, the selectivity of the gluconate is relatively lower, which might be ascribed to the larger size of Au nanoparticles. Several studies demonstrated that the Au nanoparticles with the diameter less than 10 nm have high performance of oxidation of glucose into gluconic acid [28,34,35]. In Au/CA electrode, the gold nanoparticles are highly dispersed on the surface of CA, with a uniform size of~10 um, approving for its high efficiency.…”