Selective oxidation of arabinose to arabinonic acid over Pd–Au catalysts supported on alumina and ceria (original) (raw)
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Oxidation of sugars from hemicelluloses represents an important lignocellulosic biomass valorization process and has been considered as an option to decrease high dependency of chemical industry on fossil feedstock. Gold nanoparticles as an arabinose oxidation catalyst under alkaline conditions result in high selectivity towards aldonic acids. In this work, kinetics of selective oxidation of L-arabinose to arabinonic acid over Au/Al 2 O 3 was studied using data from experiments in a semibatch shaker reactor under pH-controlled conditions at atmospheric pressure. A novel model considering molecular adsorption of oxygen, production of H 2 O 2 and different skeletal isomers of arabinose as reactants is reported. An experiment with D-arabinose was carried out in a conventional semibatch reactor and the model adequately predicted the results.
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Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO 4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO 4 ·2H 2 O + 0.5 M H 2 SO 4 solution for various deposition times at a submonolayer coverage. Topography of obtained Pd/Au(poly) surfaces was observed by tapping mode atomic force microscopy (AFM), while chemical surface composition changes were detected by simultaneously performed phase AFM. Deposited Pd islands were nonuniform in size and randomly distributed over the gold substrate. Size and number of Pd islands increase with the increase of the deposition time, and consequently surface coverage increases too. Deposited Pd was also identified by the changes in cyclic voltammetry (CV) profiles from which an active surface area was estimated. Obtained Pd/Au(poly) surfaces have shown a significant catalytic activity towards oxygen reduction reaction which increases with the increase of Pd islands coverage. The initial potential of ORR was shifted positively, while reaction pathway changes from 2e-reduction on pure gold to 4e-reduction on Pd modified gold. Additionally, obtained Pd/Au(poly) surfaces have shown a significant activity towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. This supports the assumption that ORR on Pd/Au(poly) occurs partly through 4e-series reduction pathway, the fraction of which increases with the increase of Pd coverage.
ACS Sustainable Chemistry & Engineering, 2018
We report herein HMF (5-hydromethylfurfural) and furfural oxidation to 2,5furandicarboxylic (FDCA) and furoic acids, respectively, in water, under base free conditions and using supported gold nanoparticles. Prepared catalysts showed high catalytic activity under environmentally friendly conditions. Especially, the use of base-free conditions enables getting rid of the most usually needed neutralization step generating salts that must be further handled/eliminated. We showed that the conversion and the selectivity to desired products are depending on the basicity of the support. To this respect, the Au/MgO catalyst was the most active sample (100% and 90% yields to furoic acid and 2,5-furandicarboxylic acid, respectively),
Development of new highly active nano gold catalysts for selective oxidation reactions
2014
I would like to begin with praising and thanking the god, Allah, the almighty for all his bounties upon me and for his assistance in my life and my study which without him this work would not have been achieved. I would like to thank many people for their help and support during my studies. I would like to greatly thank my supervisor, Prof. Graham Hutchings, for his invaluable support, guidance and encouragement throughout my PhD degree journey. I am also deeply grateful to Dr. Meenakshisundaram Sankar and Dr. Peter J. Miedziak for their supervision, input and support during my PhD study. I would also like to thank my cosupervisor Prof. David W. Knight for his suggestions and invaluable advice throughout this study. I would also like to extend my gratitude to Prof. Christopher Kiely and his group for STEM, Dr. David Morgan for XPS, James Pritchard for H 2 O 2 testing and Dr Jennifer Edwards for the thesis correction. I shall also thank the department technical staff in chemistry school. Moreover, I would like to thank all the members of GJH group in lab 1.88, 1.86 and 0.90 for a nice time we spent together with special mention to
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Catalysis Today, 2002
New applications of gold catalysts for selective oxidation of organic molecules are reported. All reactions investigated were performed using molecular oxygen in aqueous solution under mild conditions. Polyhydroxylated aliphatic molecules can be oxidised to monocarboxylates with high selectivity towards the primary alcoholic group in the presence of alkali, whereas the phenyl group enhances the reactivity of a benzylic alcoholic group as it limits the selectivity to mandelate starting from phenyl-1,2-ethanediol. ␣-and -aminoalcohols react slowly with oxygen in the absence and quickly in the presence of alkali to produce the corresponding aminoacid derivatives. Aliphatic aldehydes and glucose are easily oxidised to free carboxylic acid. A comparison of gold catalysts and conventional Pd and Pt monometallic, bimetallic and tricomponent catalysts has, in some cases, been done.
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We present a small review of recent density-functional-theory (DFT) studies of the reactivity towards CO oxidation of supported Au nanoparticles. The possible structure of the periphery of the interface between a Au particle and an oxide support is discussed. A certain structure, in which low coordinated Au atoms are overhanging the support without binding directly to the oxide atoms, is argued to be prototypical of medium-sized Au particles. This structure is shown to be particularly active both at the edges and at the corners of Au particles. Examples from the literature of Au systems supported on MgO(1 0 0) and rutile-TiO 2 (1 1 0) are reviewed and new data are given for the reactivity of facet, edge, and corner sites of a Au 34 cluster supported on MgO(1 0 0). On the non-reducible oxide support, MgO(1 0 0), the CO oxidation is found to occur via CO adsorption to the Au particles and subsequent CO-promoted O 2 capture and formation of a COÁO 2 reaction intermediate complex. On the reducible oxide support, TiO 2 (1 1 0), the O 2 is found to adsorb independently of the CO. However, on this support, the reaction still proceeds via COÁO 2 formation rather than via O 2 dissociation. #