The Experts below are selected from a list of 13131 Experts worldwide ranked by ideXlab platform
Asterios Gavriilidis - One of the best experts on this subject based on the ideXlab platform.
-
Aerobic Oxidation of Benzyl Alcohol in a Continuous Catalytic Membrane Reactor
2019Co-Authors: Achilleas Constantinou, Peter Ellis, Simon Kuhn, Baldassarre Venezia, Asterios GavriilidisAbstract:A catalytic membrane reactor with a Au–Pd catalyst, impregnated at the inner side of the membrane, was studied in the catalytic oxidation of Benzyl Alcohol in flow. The reactor comprised of four concentric sections. The liquid substrate flowed in the annulus created by an inner tube and the membrane. The membrane consisted of 3 layers of α-alumina and a titania top layer with 5 nm average pore size. Oxygen was fed on the outer side of the membrane, and its use allowed the controlled contact of the liquid and the gas phase. Experiments revealed excellent stability of the impregnated membrane and selectivities to benzaldehyde were on average > 95%. Increasing the pressure of the gas phase and decreasing liquid flowrates and Benzyl Alcohol concentration resulted in an increased conversion, while selectivities to benzaldehyde remained constant and in excess of 95%.
-
continuous flow aerobic oxidation of Benzyl Alcohol on ru al2o3 catalyst in a flat membrane microchannel reactor an experimental and modelling study
2019Co-Authors: Gaowei Wu, Peter Ellis, Simon Kuhn, Achilleaa Constantinou, Asterios GavriilidisAbstract:A flat Teflon AF-2400 membrane microchannel reactor was experimentally and theoretically investigated for aerobic oxidation of Benzyl Alcohol on a 5 wt% Ru/Al2O3 catalyst. The reactor consisted of gas and liquid channels (75 mm (L) × 3 mm (W) × 1 mm (D)), separated by a 0.07 mm thick semipermeable Teflon AF-2400 flat membrane, which allowed continuous supply of oxygen during the reaction and imultaneously avoided direct mixing of gaseous oxygen with organic reactants. A catalyst stability test was first carried out, and the experimental data obtained were used to estimate the kinetics of Benzyl Alcohol oxidation with a 2D reactor model. Using these kinetics, predictions from the 2D reactor model agreed well with the experimental data obtained at different liquid flow rates and oxygen pressures. The mass transfer and catalytic reaction in the membrane microchannel reactor were then theoretically studied by changing the membrane thickness, the liquid channel depth, and the reaction rate coefficient. Oxygen transverse mass transport in the catalyst bed was found to be the controlling process for the system investigated, and decreasing the liquid channel depth is suggested to improve the oxygen supply and enhance the Benzyl Alcohol conversion in the membrane reactor.
-
continuous heterogeneously catalyzed oxidation of Benzyl Alcohol in a ceramic membrane packed bed reactor
2015Co-Authors: Achilleas Constantinou, Donald Bethell, Peter Ellis, Simon Kuhn, Albert Corredera, Graham J Hutchings, Asterios GavriilidisAbstract:A ceramic membrane reactor was investigated for the continuous catalytic oxidation of Benzyl Alcohol with oxygen. The reactor had a concentric configuration. An inner tube created an annulus for the catalyst packed-bed (0.9 wt % Au− Pd/TiO2, particle size 90−125 μm) through which the liquid phase (Benzyl Alcohol, neat or dissolved in o-xylene) flowed. This was followed by the tubular ceramic membrane, which consisted of layers of alumina and a zirconia top layer with a nominal average pore size of 50 nm. The role of the membrane was to provide an interface for gas and liquid to come in contact. Pure oxygen was fed to the opposite side of the membrane in the outer shell of the reactor. Temperature affected conversion but not selectivity, possibly because of insufficient supply of oxygen. However, increasing catalyst contact time or decreasing Benzyl Alcohol concentration improved selectivity and conversion, indicating that a key parameter was the balance between oxygen supply by the membrane vs oxygen demand by the reaction. By adjusting the operating parameters, reaction performance improved. Selectivity to benzaldehyde 88% and conversion of Benzyl Alcohol 75% were obtained at 3.2 bara of gas pressure, 24444 gcat·s/gAlcohol catalyst contact time, 0.5 M Benzyl Alcohol concentration, and temperature of 120 °C. This performance was comparable to simulated trickle bed operation, where oxygen and substrate were premixed before entering the catalyst packed bed. The membrane reactor offers safer operation, since flammable oxygen/organic mixtures formed in the trickle bed are avoided.
-
selective suppression of disproportionation reaction in solvent less Benzyl Alcohol oxidation catalysed by supported au pd nanoparticles
2013Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Moataz Morad, Donald Bethell, Christopher J. Kiely, David W. Knight, Peter J. Miedziak, Qian He, Stuart Hamilton Taylor, Asterios GavriilidisAbstract:Disproportionation of Benzyl Alcohol has been identified as the source of toluene formation in the solvent free oxidation of Benzyl Alcohol using supported gold palladium catalysts. There is a slight increase in the disproportionation reaction, and hence the toluene selectivity, when this reaction is performed in a continuous mode using a micro-packed bed reactor when compared to the same reaction performed in a conventional glass stirred batch reactor. Oxidation and disproportionation reactions respond slightly differently to the changes in reaction parameters, like oxygen concentration and pressure, when a micro packed bed reactor was used instead of a conventional glass stirred reactor. When MgO supported gold–palladium catalysts were used for this reaction, the toluene selectivity reduced substantially at the cost of conversion.
-
Single and multiphase catalytic oxidation of Benzyl Alcohol by tetrapropylammonium perruthenate in a mobile microreactor system
2006Co-Authors: Asterios GavriilidisAbstract:A mobile microreactor system, with flow and temperature control for organic synthesis, is described. The system can be used anywhere a venting outlet is available. The microreactors can be operated in different flow patterns (continuous flow, stop-flow, or programmed-flow) providing reaction times from a few minutes to a few hours. The system was tested for the catalytic oxidation of Benzyl Alcohol to benzaldehyde by tetrapropylammonium perruthenate (TPAP) with N-methyl-morpholine-N-oxide in the liquid phase under stop-flow mode and on supported TPAP with oxygen under continuous flow mode. The conversion of Benzyl Alcohol in the microreactor was close to that of a small batch reactor for the liquid phase reaction. For the multiphase reaction, a conversion of 30-40% was obtained with residence times below 1 min.
Graham J Hutchings - One of the best experts on this subject based on the ideXlab platform.
-
continuous heterogeneously catalyzed oxidation of Benzyl Alcohol in a ceramic membrane packed bed reactor
2015Co-Authors: Achilleas Constantinou, Donald Bethell, Peter Ellis, Simon Kuhn, Albert Corredera, Graham J Hutchings, Asterios GavriilidisAbstract:A ceramic membrane reactor was investigated for the continuous catalytic oxidation of Benzyl Alcohol with oxygen. The reactor had a concentric configuration. An inner tube created an annulus for the catalyst packed-bed (0.9 wt % Au− Pd/TiO2, particle size 90−125 μm) through which the liquid phase (Benzyl Alcohol, neat or dissolved in o-xylene) flowed. This was followed by the tubular ceramic membrane, which consisted of layers of alumina and a zirconia top layer with a nominal average pore size of 50 nm. The role of the membrane was to provide an interface for gas and liquid to come in contact. Pure oxygen was fed to the opposite side of the membrane in the outer shell of the reactor. Temperature affected conversion but not selectivity, possibly because of insufficient supply of oxygen. However, increasing catalyst contact time or decreasing Benzyl Alcohol concentration improved selectivity and conversion, indicating that a key parameter was the balance between oxygen supply by the membrane vs oxygen demand by the reaction. By adjusting the operating parameters, reaction performance improved. Selectivity to benzaldehyde 88% and conversion of Benzyl Alcohol 75% were obtained at 3.2 bara of gas pressure, 24444 gcat·s/gAlcohol catalyst contact time, 0.5 M Benzyl Alcohol concentration, and temperature of 120 °C. This performance was comparable to simulated trickle bed operation, where oxygen and substrate were premixed before entering the catalyst packed bed. The membrane reactor offers safer operation, since flammable oxygen/organic mixtures formed in the trickle bed are avoided.
-
surface functionalized tio 2 supported pd catalysts for solvent free selective oxidation of Benzyl Alcohol
2015Co-Authors: Patcharaporn Weerachawanasak, Peter J. Miedziak, Graham J Hutchings, Jennifer K Edwards, Simon A Kondrat, Joongjai PanpranotAbstract:Pd catalysts supported on TiO2 functionalized with various amounts of 3-aminopropyltriethoxysilane (APTES) were prepared using a post-synthesis grafting method combined with electroless deposition of Pd. As revealed by the Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) results, monolayer APTES grafting was obtained using 0.005 mmol APTES on 1.5 g TiO2 support. Excess amounts of APTES resulted in both multilayer and reversed attachment, which NH2 attached to the TiO2 surface rather than giving free NH2 termination. The catalytic activity in the solvent-free selective oxidation of Benzyl Alcohol was correlated well with the highest amount of Pd deposited as well as the formation of small and uniform Pd nanoclusters with narrow particle size distribution (average diameter 3.4 nm) on the 1%Pd/TiO2-0.005APTES. Increasing of surface basicity via the hydrolysis of amino groups (single bondNH2) is suggested to enhance the dehydrogenation of Benzyl Alcohol, and as a consequence the selectivity toward benzaldehyde increased for all the APTES-modified TiO2 supported Pd catalysts. In addition, the combination of metallic Pd0 and PdOx (Pd2+/Pd4+) species gave high catalytic activity in the Benzyl Alcohol oxidation, emphasizing that the reduction of PdOx species by the adsorbed Benzyl Alcohol is an essential step to form highly active metallic Pd0 sites.
-
the benzaldehyde oxidation paradox explained by the interception of peroxy radical by Benzyl Alcohol
2014Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Donald Bethell, David W. Knight, Emma Carter, Damien Martin Murphy, Graham J HutchingsAbstract:Benzaldehyde readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature. Yet it can be formed in high yield from, for example, Benzyl Alcohol by oxidation using a variety of procedures and catalysts. Here we report the evidence to resolve this apparent paradox. It is confirmed that Benzyl Alcohol (and a number of other Alcohols), even at low concentrations in benzaldehyde, inhibits the autoxidation. Furthermore we report on the structural features required for inhibition. Electron paramagnetic resonance spin trapping experiments demonstrate that Benzyl Alcohol intercepts, by hydrogen atom transfer, the benzoylperoxy radicals that play a key role in benzaldehyde autoxidation. A similar inhibition effect has also been observed for the aliphatic octanal/1-octanol system.
-
controlling the duality of the mechanism in liquid phase oxidation of Benzyl Alcohol catalysed by supported au pd nanoparticles
2011Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Donald Bethell, Christopher J. Kiely, David W. Knight, Stuart Hamilton Taylor, Ramchandra Tiruvalam, Graham J HutchingsAbstract:In the solvent-free oxidation of Benzyl Alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of Benzyl Alcohol to benzaldehyde by O2, whereas the second is the disproportionation of two molecules of Benzyl Alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O2 increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
-
solvent free liquid phase oxidation of Benzyl Alcohol using au supported catalysts prepared using a sol immobilization technique
2007Co-Authors: Nikolaos Dimitratos, Laura Prati, Jose Antonio Lopezsanchez, David J Morgan, Albert Frederick Carley, Graham J HutchingsAbstract:Solvent free oxidation of Benzyl Alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for Benzyl Alcohol oxidation.
Naijia Guan - One of the best experts on this subject based on the ideXlab platform.
-
supported pd catalysts for solvent free Benzyl Alcohol selective oxidation effects of calcination pretreatments and reconstruction of pd sites
2012Co-Authors: Xueming Wang, Naijia GuanAbstract:Abstract Pd catalysts supported on Al 2 O 3 and TiO 2 have been prepared by wet impregnation and studied for the solvent-free selective oxidation of Benzyl Alcohol by molecular oxygen. High activity as well as high selectivity to benzaldehyde can be obtained and the calcination pretreatments show distinct effects on the catalytic activities of supported Pd catalysts. Supported Pd catalysts before and after Benzyl Alcohol oxidation are characterized by means of XPS, FTIR spectra of CO adsorption and O 2 -TPD. The results clearly show that the palladium sites in supported Pd catalysts undergo reconstruction during Benzyl Alcohol oxidation. Based on the catalytic and characterization results, the possible Benzyl Alcohol oxidation reaction pathways and the active palladium sites in supported Pd catalysts for Benzyl Alcohol oxidation are discussed.
-
solvent free selective photocatalytic oxidation of Benzyl Alcohol over modified tio2
2011Co-Authors: Wei Feng, Naijia GuanAbstract:Heterogeneous photocatalysis offers a promising route to realize green oxidation processes in organic synthesis. In this research, the solvent-free selective photocatalytic oxidation of Benzyl Alcohol to benzaldehyde in the presence molecular oxygen was studied by using TiO2 and modified TiO2 as photocatalysts. The surface modification of TiO2 by transition metal clusters dramatically enhanced the photocatalytic oxidation activity. Ir/TiO2 prepared by photodeposition showed a remarkably high activity for the photocatalytic oxidation of Benzyl Alcohol, and an average reaction rate of 14538 μmol h−1 gcat−1 could be obtained. The effect of preparation method, iridium loading and reaction conditions on the catalytic performance of Ir/TiO2 is investigated in detail. Based on the catalytic and characterization results, the problem of product selectivity and the reaction mechanism of the photocatalytic oxidation of Benzyl Alcohol over Ir/TiO2 are discussed.
Annegret Stark - One of the best experts on this subject based on the ideXlab platform.
-
selective catalytic oxidation of Benzyl Alcohol and alkylbenzenes in ionic liquids
2002Co-Authors: Kenneth R Seddon, Annegret StarkAbstract:Industrially performed catalytic oxidation reactions often suffer from drawbacks such as poor conversion and selectivity due to over-oxidation, corrosive reaction media, lack of solvent and catalyst recycling, and negative environmental impact due to evaporation of the solvents. In order to provide a methodology that addresses these problems, ionic liquids have been investigated as reaction media. For the example of the oxidation of Benzyl Alcohol to benzaldehyde (dehydrogenation), it was shown that the palladium metal catalysed oxidation can be brought about, leading to better TOFs than those observed in dimethyl sulfoxide, with the added advantage of facile catalyst and solvent recycling. It was found that the selectivity to benzaldehyde is strongly dependent on the level of chloride ion, which leads to the formation of diBenzyl ether. Secondly, the amount of water present in the ionic liquid determines the extent of benzoic acid formation. Interestingly, ionic liquids are able to deactivate the water formed in the oxidation of Benzyl Alcohol and thus prevent it from further reaction to benzoic acid. The oxidation of toluene and ethylbenzene showed that the introduction of oxygen into the molecule is feasible using the same methodology.
Donald Bethell - One of the best experts on this subject based on the ideXlab platform.
-
continuous heterogeneously catalyzed oxidation of Benzyl Alcohol in a ceramic membrane packed bed reactor
2015Co-Authors: Achilleas Constantinou, Donald Bethell, Peter Ellis, Simon Kuhn, Albert Corredera, Graham J Hutchings, Asterios GavriilidisAbstract:A ceramic membrane reactor was investigated for the continuous catalytic oxidation of Benzyl Alcohol with oxygen. The reactor had a concentric configuration. An inner tube created an annulus for the catalyst packed-bed (0.9 wt % Au− Pd/TiO2, particle size 90−125 μm) through which the liquid phase (Benzyl Alcohol, neat or dissolved in o-xylene) flowed. This was followed by the tubular ceramic membrane, which consisted of layers of alumina and a zirconia top layer with a nominal average pore size of 50 nm. The role of the membrane was to provide an interface for gas and liquid to come in contact. Pure oxygen was fed to the opposite side of the membrane in the outer shell of the reactor. Temperature affected conversion but not selectivity, possibly because of insufficient supply of oxygen. However, increasing catalyst contact time or decreasing Benzyl Alcohol concentration improved selectivity and conversion, indicating that a key parameter was the balance between oxygen supply by the membrane vs oxygen demand by the reaction. By adjusting the operating parameters, reaction performance improved. Selectivity to benzaldehyde 88% and conversion of Benzyl Alcohol 75% were obtained at 3.2 bara of gas pressure, 24444 gcat·s/gAlcohol catalyst contact time, 0.5 M Benzyl Alcohol concentration, and temperature of 120 °C. This performance was comparable to simulated trickle bed operation, where oxygen and substrate were premixed before entering the catalyst packed bed. The membrane reactor offers safer operation, since flammable oxygen/organic mixtures formed in the trickle bed are avoided.
-
the benzaldehyde oxidation paradox explained by the interception of peroxy radical by Benzyl Alcohol
2014Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Donald Bethell, David W. Knight, Emma Carter, Damien Martin Murphy, Graham J HutchingsAbstract:Benzaldehyde readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature. Yet it can be formed in high yield from, for example, Benzyl Alcohol by oxidation using a variety of procedures and catalysts. Here we report the evidence to resolve this apparent paradox. It is confirmed that Benzyl Alcohol (and a number of other Alcohols), even at low concentrations in benzaldehyde, inhibits the autoxidation. Furthermore we report on the structural features required for inhibition. Electron paramagnetic resonance spin trapping experiments demonstrate that Benzyl Alcohol intercepts, by hydrogen atom transfer, the benzoylperoxy radicals that play a key role in benzaldehyde autoxidation. A similar inhibition effect has also been observed for the aliphatic octanal/1-octanol system.
-
selective suppression of disproportionation reaction in solvent less Benzyl Alcohol oxidation catalysed by supported au pd nanoparticles
2013Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Moataz Morad, Donald Bethell, Christopher J. Kiely, David W. Knight, Peter J. Miedziak, Qian He, Stuart Hamilton Taylor, Asterios GavriilidisAbstract:Disproportionation of Benzyl Alcohol has been identified as the source of toluene formation in the solvent free oxidation of Benzyl Alcohol using supported gold palladium catalysts. There is a slight increase in the disproportionation reaction, and hence the toluene selectivity, when this reaction is performed in a continuous mode using a micro-packed bed reactor when compared to the same reaction performed in a conventional glass stirred batch reactor. Oxidation and disproportionation reactions respond slightly differently to the changes in reaction parameters, like oxygen concentration and pressure, when a micro packed bed reactor was used instead of a conventional glass stirred reactor. When MgO supported gold–palladium catalysts were used for this reaction, the toluene selectivity reduced substantially at the cost of conversion.
-
controlling the duality of the mechanism in liquid phase oxidation of Benzyl Alcohol catalysed by supported au pd nanoparticles
2011Co-Authors: Meenakshisundaram Sankar, Ewa Nowicka, Donald Bethell, Christopher J. Kiely, David W. Knight, Stuart Hamilton Taylor, Ramchandra Tiruvalam, Graham J HutchingsAbstract:In the solvent-free oxidation of Benzyl Alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of Benzyl Alcohol to benzaldehyde by O2, whereas the second is the disproportionation of two molecules of Benzyl Alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O2 increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.