Glycerol Oxidation over Supported Gold Catalysts: The Combined Effect of Au Particle Size and Basicity of Support

Abstract

Gold nanoparticles supported on various oxides (CeO2, CeO2/TiO2, MgO, MgO/TiO2, La2O3, La2O3/TiO2) (with 4 wt.% Au loading) were investigated in the liquid (aqueous) phase oxidation of glycerol by molecular oxygen under mild conditions, in the presence of alkaline earth (CaO, SrO and MgO) or alkaline (NaOH) bases. Full conversion and selectivity between 38 and 68% to sodium glycerate were observed on different Au supported catalysts (Au/MgO/TiO2, Au/La2O3/TiO2, Au/CeO2 and Au/CeO2/TiO2). The combined effect of Au particle size and basicity of the support was suggested as the determining factor of the activity. Agglomeration of gold nanoparticles, found after the reaction, led to the deactivation of the catalysts, which prevents the further oxidation of sodium glycerate into sodium tartronate. Promising results were obtained with the use of alkaline earth bases (CaO, SrO, MgO), leading to the formation of free carboxylic acids instead of salts, which are formed in the presence of the more usual base, NaOH.

On the Mechanistic Origins of the pH-Dependency in Au-Catalyzed Glycerol Electro-Oxidation: Insight from First Principles Calculations

“…As a result, GLD cannot be easily formed in acidic environments and Au-catalyzed EOG under these conditions should lead only to DHA and DHA-derived products that is supported by previous experimental and computational studies. 22 Overall, our findings on the tautomerism in EOG agree with experimental results on thermal GLY conversion, 80,81 where the pivotal role of the DHA-GLD keto-enol tautomerism for pH-dependent selectivity has been reported at high pH.…”

“…In alkaline media, GLA has been identified as the main product or reaction intermediate towards more oxygenated species but the formation of DHA cannot be ruled out a priori or based on current experimental data. 1,7,18,19,21,80,81 Figure 6 18,19,29,[40][41][42]82 This clearly indicates that both GLY and OH are simultaneously present on the surface at the experimentally relevant EOG conditions around the onset potential region in > 0.7 V RHE . Therefore, the computational model for Au-catalyzed alkaline EOG should explicitly take into account the influence of OH groups and thus two OH groups, corresponding to 1/6 ML coverage, were added to the Au(111) surface.…”

“…This indicates that DHA and GLD can be easily inter-converted under alkaline conditions as suggested for thermocatalytic conversion of GLY. 80,81…”

Oxidation of 5-Hydroxymethylfurfural on Supported Ag, Au, Pd and Bimetallic Pd-Au Catalysts: Effect of the Support

“…The screening started with previously investigated catalysts: Au supported on unmodified and modified titania (M x O y /TiO 2 ) materials used for aerobic liquid phase oxidation of different type of alcohols: n-octanol, glycerol and betulin, under mild conditions [20][21][22][23]. Briefly, the best catalytic performance among Au catalysts supported on modified titania were reached with catalysts modified with lanthanum oxide (Au/La 2 O 3 /TiO 2 ), regardless of the alcohol type studied [20][21][22][23]. In addition, recently obtained results in betulin oxidation using Au/Alumina catalysts revealed that Au/AlOOH-C catalyst is superior to Au/La 2 O 3 /TiO 2 in both activity and selectivity [24].…”

“…Au was loaded (nominal loading 4 wt.%) on M x O y /TiO 2 and various alumina supports using HAuCl 4 •3H 2 O (Merck, Darmstadt, Germany) as precursor, by the depositionprecipitation method with urea (Merck, Darmstadt, Germany) in the absence of light, according to the procedure described in previous works [20][21][22][23][24]. Gold catalyst samples (0.5 g) were then pretreated in a hydrogen atmosphere for 1 h at 300 • C (15% H 2 in Ar, 300 mL/min flow rate) for the decomposition of the hydrolysis products of the complex of gold (III) with urea on the support surface [63].…”