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Peter Schieberle - One of the best experts on this subject based on the ideXlab platform.
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characterization of the key aroma compounds in beef and pork vegetable gravies a la chef by application of the aroma extract dilution analysis
Journal of Agricultural and Food Chemistry, 2009Co-Authors: Monika Christlbauer, Peter SchieberleAbstract:By application of the aroma extract dilution analysis (AEDA) on an aroma distillate isolated from a freshly prepared, stewed beef/vegetable gravy, 52 odor-active compounds were detected in the flavor dilution (FD) factor range of 4−4096. On the basis of high FD factors in combination with the results of the identification experiments, 3-(methylthio)propanal (cooked potato), 3-mercapto-2-methylpentan-1-ol (gravy-like), (E,E)-2,4-decadienal (deep-fried, fatty), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (lovage-like), vanillin (vanilla-like), (E,E)-2,4-nonadienal (deep-fried), and (E)-2-undecenal (metallic) are suggested as key contributors to the aroma of the gravy. To get an insight into the role of the vegetables as sources of gravy odorants, a beef gravy was prepared without vegetables. The AEDA results revealed that, in particular, onions and leek are important sources of gravy aroma compounds, adding particularly the very potent, gravy-like smelling 3-mercapto-2-methylpentan-1-ol to the overall aroma profi...
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quantitation of the intense aroma compound 3 mercapto 2 methylpentan 1 ol in raw and processed onions allium cepa of different origins and in other allium varieties using a stable isotope dilution assay
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Michael Granvogl, Monika Christlbauer, Peter SchieberleAbstract:A stable isotope dilution assay was developed for the quantitation of the potent onion odorant 3-mercapto-2-methylpentan-1-ol (1) using mass chromatography and synthesized [2H2]-3-mercapto-2-methyl...
Wilhelm Pickenhagen - One of the best experts on this subject based on the ideXlab platform.
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3 mercapto 2 methylpentan 1 ol a new powerful aroma compound
Journal of Agricultural and Food Chemistry, 2000Co-Authors: Sabine Widder, Christopher Sabater Luntzel, Thomas Dittner, Wilhelm PickenhagenAbstract:3-Mercapto-2-methylpentan-1-ol was first detected in a complex thermally processed flavor and finally isolated from raw onions. The chemical structure of this new compound was identified by MS and ...
Selim Alayoglu - One of the best experts on this subject based on the ideXlab platform.
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Reforming of C-6 Hydrocarbons Over Model Pt Nanoparticle Catalysts
'Springer Science and Business Media LLC', 2015Co-Authors: Selim Alayoglu, Nathan Musselwhite, Vv Pushkarev, Sk Beaumont, Ga SomorjaiAbstract:Size-controlled model Pt nanoparticle catalysts, synthesized by colloidal chemistry, were used to study the hydrogenative reforming of three C-6 hydrocarbons in mixtures with 5:1 excess of H-2: methylcyclopentane, n-hexane and 2-Methylpentane. We found a strong particle size dependence on the distribution of different reaction products for the hydrogenolysis of methylcyclopentane. The reactions of 50 Torr methylcyclopentane in 250 Torr H-2 at 320 A degrees C, using 1.5 and 3.0 nm Pt nanoparticles produced predominantly C-6 isomers, especially 2-Methylpentane, whereas 5.2 and 11.3 nm Pt nanoparticles were more selective for the formation of benzene. For the hydrogenolysis of n-hexane and 2-Methylpentane, strong particle size effects on the turnover rates were observed. Hexane and 2-Methylpentane reacted up to an order of magnitude slower over 3.0 nm Pt than over the other particle sizes. At 360 A degrees C the isomerization reactions were more selective than the other reaction pathways over 3.0 nm Pt, which also yielded relatively less benzene.close8
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high temperature catalytic reforming of n hexane over supported and core shell pt nanoparticle catalysts role of oxide metal interface and thermal stability
Nano Letters, 2014Co-Authors: Qiao Zhang, Selim Alayoglu, Nathan Musselwhite, Jaeyoun Shin, Gabor A. SomorjaiAbstract:Designing catalysts with high thermal stability and resistance to deactivation while simultaneously maintaining their catalytic activity and selectivity is of key importance in high-temperature reforming reactions. We prepared Pt nanoparticle catalysts supported on either mesoporous SiO2 or TiO2. Sandwich-type Pt core@shell catalysts (SiO2@Pt@SiO2 and SiO2@Pt@TiO2) were also synthesized from Pt nanoparticles deposited on SiO2 spheres, which were encapsulated by either mesoporous SiO2 or TiO2 shells. n-Hexane reforming was carried out over these four catalysts at 240–500 °C with a hexane/H2 ratio of 1:5 to investigate thermal stability and the role of the support. For the production of high-octane gasoline, branched C6 isomers are more highly desired than other cyclic, aromatic, and cracking products. Over Pt/TiO2 catalyst, production of 2-Methylpentane and 3-methylpentane via isomerization was increased selectively up to 420 °C by charge transfer at Pt–TiO2 interfaces, as compared to Pt/SiO2. When thermal...
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Reforming of C_6 Hydrocarbons Over Model Pt Nanoparticle Catalysts
Topics in Catalysis, 2012Co-Authors: Selim Alayoglu, Vladimir V. Pushkarev, Nathan Musselwhite, Simon K. Beaumont, Gabor A. SomorjaiAbstract:Size-controlled model Pt nanoparticle catalysts, synthesized by colloidal chemistry, were used to study the hydrogenative reforming of three C_6 hydrocarbons in mixtures with 5:1 excess of H_2: methylcyclopentane, n -hexane and 2-Methylpentane. We found a strong particle size dependence on the distribution of different reaction products for the hydrogenolysis of methylcyclopentane. The reactions of 50 Torr methylcyclopentane in 250 Torr H_2 at 320 °C, using 1.5 and 3.0 nm Pt nanoparticles produced predominantly C_6 isomers, especially 2-Methylpentane, whereas 5.2 and 11.3 nm Pt nanoparticles were more selective for the formation of benzene. For the hydrogenolysis of n-hexane and 2-Methylpentane, strong particle size effects on the turnover rates were observed. Hexane and 2-Methylpentane reacted up to an order of magnitude slower over 3.0 nm Pt than over the other particle sizes. At 360 °C the isomerization reactions were more selective than the other reaction pathways over 3.0 nm Pt, which also yielded relatively less benzene.
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size and shape dependence on pt nanoparticles for the methylcyclopentane hydrogen ring opening ring enlargement reaction
Catalysis Letters, 2011Co-Authors: Selim Alayoglu, Ga Somorjai, C Aliaga, C SprungAbstract:Monodisperse Pt nanoparticles (NPs) with well-controlled sizes in the range between 1.5 and 10.8 nm, and shapes of octahedron, cube, truncated octahedron and spheres (~6 nm) were synthesized employing the polyol reduction strategy with polyvinylpyrrolidone (PVP) as the capping agent. We characterized the as-synthesized Pt nanoparticles using transmission electron microscopy (TEM), high resolution TEM, sum frequency generation vibrational spectroscopy (SFGVS) using ethylene/H2 reaction as the surface probe, and the catalytic ethylene/H2 reaction by means of measuring surface concentration of Pt. The nanoparticles were supported in mesoporous silica (SBA-15 or MCF-17), and their catalytic reactivity was evaluated for the methylcyclopentane (MCP)/H2 ring opening/ring enlargement reaction using 10 torr MCP and 50 torr H2 at temperatures between 160 and 300 °C. We found a strong correlation between the particle shape and the catalytic activity and product distribution for the MCP/H2 reaction on Pt. At temperatures below 240 °C, 6.3 nm Pt octahedra yielded hexane, 6.2 nm Pt truncated octahedra and 5.2 nm Pt spheres produced 2-Methylpentane. In contrast, 6.8 nm Pt cubes led to the formation of cracking products (i.e. C1–C5) under similar conditions. We also detected a weak size dependence of the catalytic activity and selectivity for the MCP/H2 reaction on Pt. 1.5 nm Pt particles produced 2-Methylpentane for the whole temperature range studied and the larger Pt NPs produced mainly benzene at temperatures above 240 °C.
Notker Rosch - One of the best experts on this subject based on the ideXlab platform.
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formation of n hexane from methylcyclopentane via a metallacyclobutane intermediate at step sites of pt surfaces mechanism from first principles calculations
Journal of Catalysis, 2013Co-Authors: Zhijian Zhao, Lyudmila V Moskaleva, Notker RoschAbstract:With periodic density functional theory calculations, we examined the ring opening of methylcyclopentane to n-hexane via an alpha gamma-adsorbed metallacyclobutane intermediate over the stepped model surface Pt(322). The crucial barrier of C-C scission along this pathway was calculated as low as 79 kJ mol(-1), that is, about 20 kJ mol(-1) lower than the value for analogous steps via alpha alpha beta beta-adsorbed intermediates on the way to 2- or 3-methylpentane on Pt(211). Thus, at step sites of Pt surfaces, formation of (unbranched) n-hexane seems to be more favorable than formation of branched hexanes. (C) 2012 Elsevier Inc. All rights reserved.
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ring opening reactions of methylcyclopentane over metal catalysts m pt rh ir and pd a mechanistic study from first principles calculations
ACS Catalysis, 2013Co-Authors: Zhijian Zhao, Lyudmila V Moskaleva, Notker RoschAbstract:Using density functional calculations we studied the conversion of methylcyclopentane to its various ring-opening products, branched and unbranched hexanes, that is, 2-Methylpentane and 3-methylpentane, as well as n-hexane. We examined four metal catalysts, M = Pt, Rh, Ir, and Pd, using slab models of flat M(111) and stepped M(211) surfaces, to describe terrace-rich large and defect-rich small M particles, respectively. As C–H bond activation and formation is rather independent of the particle structure, we focused on C–C bond scission which is expected to be structure sensitive. The barriers of C–C bond scission indeed vary from ∼20 kJ mol–1 to ∼140 kJ mol–1 on various sites of these metal surfaces. In general, lower activation energies were calculated for Rh and Ir surfaces, in agreement with the higher experimental activity of these two metals compared to Pt and Pd. From the calculated C–C bond breaking barriers, we were able to rationalize the selectivity toward different ring-opening products, as obs...
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tuning the selectivity for ring opening reactions of methylcyclopentane over pt catalysts a mechanistic study from first principles calculations
Journal of Catalysis, 2012Co-Authors: Zhijian Zhao, Lyudmila V Moskaleva, Notker RoschAbstract:Abstract Using density functional calculations, we studied the conversion of methylcyclopentane to its ring-opening products: branched hexanes [2-Methylpentane (2MP), 3-methylpentane (3MP)], as well as unbranched n-hexane (nHx). We employed flat Pt(1 1 1) and stepped Pt(2 1 1) to describe terrace-rich large and defect-rich small Pt particles, respectively. On Pt(1 1 1), the barriers of all elementary steps for the paths leading to branched hexanes lie below 90 kJ mol−1, while the formation of nHx features a barrier of 116 kJ mol−1 in its C–C bond scission step. This higher barrier impedes the formation of nHx on Pt(1 1 1) and thus rationalizes the experimental observations that terrace-rich large Pt particles selectively produce branched hexanes. However, on Pt(2 1 1), the barrier of C–C scission for the formation of nHx decreases to 94 kJ mol−1, thus implying enhanced formation of nHx over the defects, in agreement with the essentially statistical product distribution observed with defect-rich small Pt particles.
Monika Christlbauer - One of the best experts on this subject based on the ideXlab platform.
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characterization of the key aroma compounds in beef and pork vegetable gravies a la chef by application of the aroma extract dilution analysis
Journal of Agricultural and Food Chemistry, 2009Co-Authors: Monika Christlbauer, Peter SchieberleAbstract:By application of the aroma extract dilution analysis (AEDA) on an aroma distillate isolated from a freshly prepared, stewed beef/vegetable gravy, 52 odor-active compounds were detected in the flavor dilution (FD) factor range of 4−4096. On the basis of high FD factors in combination with the results of the identification experiments, 3-(methylthio)propanal (cooked potato), 3-mercapto-2-methylpentan-1-ol (gravy-like), (E,E)-2,4-decadienal (deep-fried, fatty), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (lovage-like), vanillin (vanilla-like), (E,E)-2,4-nonadienal (deep-fried), and (E)-2-undecenal (metallic) are suggested as key contributors to the aroma of the gravy. To get an insight into the role of the vegetables as sources of gravy odorants, a beef gravy was prepared without vegetables. The AEDA results revealed that, in particular, onions and leek are important sources of gravy aroma compounds, adding particularly the very potent, gravy-like smelling 3-mercapto-2-methylpentan-1-ol to the overall aroma profi...
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quantitation of the intense aroma compound 3 mercapto 2 methylpentan 1 ol in raw and processed onions allium cepa of different origins and in other allium varieties using a stable isotope dilution assay
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Michael Granvogl, Monika Christlbauer, Peter SchieberleAbstract:A stable isotope dilution assay was developed for the quantitation of the potent onion odorant 3-mercapto-2-methylpentan-1-ol (1) using mass chromatography and synthesized [2H2]-3-mercapto-2-methyl...
