Oxidation of polyols using Au-Pd and Au-Pt alloy supported nanocrystals
Peter Miedziaka, Gemma L. Bretta, Yulia Ryabenkovaa, Nikolaos Dimitratosa, Jose A. Lopez-Sancheza, Meenakshisundaram Sankara, Albert F. Carleya, Ram C. Tiruvalamb, Andrew A. Herzingc, Christopher J. Kielyb, David W. Knighta, Stuart H. Taylora, and Graham J. Hutchingsa*
a School of Chemistry, Cardiff University, Cardiff Catalysis Institute,Main Building, Park Place, Cardiff, CF10 3AT, UK
b Center for Advanced Materials and Nanotechnology, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195, USA
c National Institute of Standards and Technology, Surface and Microanalysis Science Division, 100 Bureau Drive, Mailstop 8371, Gaithersburg, MD 20899-8371, USA
Graham J. Hutchings: phone +44 (0)29 2087 4059, fax: +44 (0)29 2087 4030, e- mail: firstname.lastname@example.org
Oxidation of organic compounds with oxidants such as air, molecular oxygen or hydrogen peroxide using supported metal catalysts for synthesising valuable intermediate products for chemical industry is well known. In recent years an increased interest has been focused on catalytic processes because these have demonstrated to be environmentally friendly and economically constructively in comparison to the stoichiometric reactions. The use of bio-renewable resources for the production of materials and chemicals continues to attract significant research attention and is highly desirable from the industry. Glycerol, a by-product from bio-diesel manufacture is a highly functionalised renewable raw material. Oxidation of glycerol leads to the formation of a number of products, such as glyceric acid, dihydroxyacetone, b-hydroxypyruvic acid, tartronic acid, glycolic acid and oxalic acid, therefore control in the distribution of products by choosing the appropriate conditions and designing the proper catalyst is desirable [1,2,3].
Moreover, glycerol can be used alternatively for the synthesis of 1,2-propane diol which can then be selectively oxidised to lactate, which has immense potential as a monomer for biodegradable polymers. The current production of lactic acid is based on the fermentation and the reaction of acetaldehyde with HCN followed by hydrolysis with sulfuric acid, which is not a desired green process. Therefore, finding an environmentally green process is desired and this can be based on the use of heterogeneous catalysts with O2 or H2O2 as oxidants. We have recently shown that the combination of gold and palladium in an alloy nanoparticle configuration leads to enhanced catalytic activity and selectivity in redox processes, such as alcohol oxidation and hydrogen peroxide synthesis [4,5]. We have shown that gold palladium alloy catalysts can be very effective for the selective oxidation of glycerol and 1,2-propanediol to glycerate and lactate [6,7]. We have extended these studies by using gold-platinum alloy catalysts. We have extensively studied the effect of support, nature of base and Au/Pt ratio in the liquid phase oxidation of glycerol and 1,2-propanediol. In addition, we have carried out the reactions in the absence of base and we have demonstrated successfully the activation of polyols in alkaline-free conditions which is important from industrial point of view. Different type of supports (acidic and basic type) have been studied and the influence of two preparation methods, wet impregnation and sol-immobilisation, are compared. The addition of platinum to gold significantly enhances the activity with respect to the corresponding Au and Pt monometallic catalysts and retains the high selectivity to glyceric and lactic acids using O2 as oxidant. Detailed STEM-HAADF studies have been carried out and have shown the presence of gold-platinum alloy on the surface of the catalyst. Comparison of the activity for C3 alcohols shows that the reactivity decreases in the order: glycerol > 1,2-propane diol The use of a sol-immobilisation preparation method as compared to impregnation leads to the highest activity alloy catalysts for glyceric and lactic acids formation from the oxidation of glycerol and 1,2-propane diol respectively and the origins of these activities based on the particle size, gold-platinum metal molar ratio, nature of metal and support are presented.
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