Oxidation of glycerol using gold–palladium alloy-supported nanocrystals
ABSTRACT The use of bio-renewable resources for the generation of materials and chemicals continues to attract significant research attention. Glycerol, a by-product from biodiesel manufacture, is a highly functionalised renewable raw material, and in this paper the oxidation of glycerol in the presence of base using supported gold, palladium and gold-palladium alloys is described and discussed. Two supports, TiO(2) and carbon, and two preparation methods, wet impregnation and sol-immobilisation, are compared and contrasted. For the monometallic catalysts prepared by impregnation similar activities are observed for Au and Pd, but the carbon-supported monometallic catalysts are more active than those on TiO(2). Glycerate is the major product and lesser amounts of tartronate, glycolate, oxalate and formate are observed, suggesting a sequential oxidation pathway. Combining the gold and palladium as supported alloy nanocrystals leads to a significant enhancement in catalyst activity and the TiO(2)-supported catalysts are significantly more active for the impregnated catalysts. The use of a sol-immobilisation preparation method as compared to impregnation leads to the highest activity alloy catalysts and the origins of these activity trends are discussed.
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- "It has been suggested that toluene and benzaldehyde are formed by competing parallel reactions of the initial benzyl intermediate via an adsorbed benzylidene species on the catalyst surface that can be either hydrogenated or oxidized . In the absence of O 2 , disproportionation of benzyl alcohol occurs with the formation of equal amounts of toluene and benzaldehyde : 2PhCH 2 OH → PhCH 3 + PhCHO + H 2 O "
ABSTRACT: Oxidation of benzyl alcohol in the absence of solvent on 1% (Au–Pd)/TiO2 catalyst with pure oxygen was performed in silicon-glass micropacked-bed reactors (MPBRs). The overall size of the microreactor chip was 23mm×23mm with a reaction channel dimension of 0.6mm (W)×0.3mm (H)×190mm (L). A pillar structure (small rectangular posts of 60μm (W)×1mm (L) 40μm apart) was incorporated near the outlet of the reaction channel to retain the catalyst. The reaction was studied in the temperature range of 80–120°C and at inlet pressures up to 5 bar(a). Benzyl alcohol conversion and benzaldehyde selectivity at 80 and 120°C obtained in MPBRs were very close to those from conventional glass stirred reactors (GSRs) apart from the selectivity at 120°C. Toluene was formed in the absence of oxygen, and its production was enhanced in the presence of oxygen. Increasing pressure improved both conversion and benzaldehyde selectivity. Mass transfer resistance in MPBRs was evaluated experimentally. The external mass transfer resistance could be ignored at a volumetric flow ratio of gas (STP) to liquid above 100, at a given liquid flow rate (0.003mL/min). The effect of catalyst particle size on the reaction was examined with two ranges of particle size: 53–63μm and 90–125μm. Lower conversion was obtained with particle sizes of 90–125μm, indicating the presence of internal mass transfer resistances. In situ Raman measurements in MPBRs were performed using a specially designed microreactor stage with a different microreactor configuration. Raman spectra obtained from liquid pockets at different points along the reaction channel could be used to obtain the benzaldehyde concentration profile along the catalyst bed. Bands due to formation of highly disordered graphitic carbon were observed on the catalyst surface.Chemical Engineering Journal 03/2011; 167(2):734-743. DOI:10.1016/j.cej.2010.08.082 · 4.32 Impact Factor
Conference Paper: Advanced mountain clustering method[Show abstract] [Hide abstract]
ABSTRACT: We introduce the advanced mountain clustering method (AMM), which uses a normalized data space, a Gaussian type mountain function and a destruction method based on a mountain slope. The proposed method is very useful because it needs just one parameter instead of three in the mountain method of Yager and Filev (1994) and finds out cluster centers without any neighboring parasitic cluster centers. In addition, we propose a noniterative selection method for the only parameter ω. Finally, computer simulation results on numerical examples are presented to show the validity of the proposed clustering methodIFSA World Congress and 20th NAFIPS International Conference, 2001. Joint 9th; 08/2001
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ABSTRACT: The use of bio-renewable resources, such as glycerol, a by-product from bio-diesel manufacture, can provide a viable way to make valuable products using greener technology. In particular, glycerol can be reduced to give 1,2-propanediol that can then be selectively oxidised to lactate, which has immense potential as a monomer for the synthesis of biodegradable polymers. We show that gold-palladium alloy catalysts can be very effective for the selective oxidation of 1,2-propanediol to lactate. Two supports, TiO2 and carbon, and two preparation methods, wet impregnation and sol-immobilisation, are contrasted. The addition of palladium to gold significantly enhances the activity and retains the high selectivity to lactate using O2 as oxidant (we observe 96% lactate selectivity at 94% conversion). Use of hydrogen peroxide is also possible but lower activities are observed as a result of the reaction conditions, but in this case no marked enhancement is observed on addition of palladium to gold. Comparison of the activity for C3 alcohols shows that the reactivity decreases in the order: glycerol > 1,2-propanediol > 1,3-propanediol ‚àº 1-propanol > 2-propanol. The use of a sol-immobilisation preparation method as compared to impregnation leads to alloy catalysts with the highest activity for lactate formation from the oxidation of 1,2-propanediol; the origins of these activity trends are discussed. ¬© 2009 The Royal Society of Chemistry.Green Chemistry 08/2009; 11(8). DOI:10.1039/b823285g · 6.85 Impact Factor