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M Guisnet - One of the best experts on this subject based on the ideXlab platform.
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methylcyclohexane transformation over hfau hbea and hmfi zeolites i Reaction Scheme and mechanisms
Industrial & Engineering Chemistry Research, 2001Co-Authors: Henrique S Cerqueira, P Magnoux, Pierre C Mihindoukoumba, M GuisnetAbstract:The transformation of methylcyclohexane was investigated at 450 °C for several contact times over six previously characterized HFAU, HMFI, and HBEA zeolites having framework Si/Al ratios either close to 15 or between 26 and 47. With all of the fresh samples, C2−C7 alkenes and alkanes, cyclopentane and methylcyclopentane (cracking products), dimethylcyclopentanes and ethylcyclopentane (isomers), and aromatics appear as primary products. Hydrogen and methane are also directly formed (methylcyclohexane protolysis) with HBEA-15, which presents very strong protonic sites, and with HMFI samples. A simplified kinetic model was established, and the rate constants leading to good agreement between experimental data and calculated yields of the main products were determined. Large differences in the rate constants are observed between the zeolite samples, which can be related to differences in acid strength and particularly to a pronounced influence of the zeolite pore structure.
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transformation of acetone over a 0 4pthmfi 60 catalyst Reaction Scheme
Journal of Molecular Catalysis A-chemical, 1997Co-Authors: Luis Melo, F. Alvarez, P Magnoux, G Giannetto, M GuisnetAbstract:The transformation of acetone was carried out over a 0.4 wt% PtHMFI catalyst (SiAl = 60) under the following conditions: flow reactor, 160°C, pressures of acetone and hydrogen equal to 0.75 and 0.25 bar, respectively. Methylisobutylketone, propane and traces of mesityloxide are observed as primary products while the other main products: 2-methylpentane and diisobutylketone result from secondary transformation of methylisobutylketone. The reactivity of the Reaction products and of probable intermediates: diacetone alcohol, isopropanol and propene was compared to that of acetone, which allows us to establish the complete Scheme of acetone transformation. Acetone is competitively transformed through bifunctional catalysis into methylisobutylketone and into propane. The limiting step of methylisobutylketone formation is acetone aldolisation over the acid sites of the catalyst while that of propane formation is acetone hydrogenation over platinum sites. Methylisobutylketone undergoes the same competitive bifunctional transformations leading to diisobutylketone (limiting step: acid coaldolisation of acetone and of methylisobutylketone) and to 2-methylpentane (limiting step: hydrogenation of methylisobutylketone).
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aromatization of propane over gahmfi catalysts Reaction Scheme nature of the dehydrogenating species and mode of coke formation
Catalysis Today, 1996Co-Authors: M Guisnet, N S GnepAbstract:Abstract The kinetic modelling of propane aromatization over a Ga/HMFI catalyst and the comparison of Ga2O3-HMFI mixtures with different compositions has allowed us to specify the respective roles of dehydrogenating species and of protonic sites. Propane aromatization over Ga/HMFI catalyst occurs mainly through a conventional bifunctional Reaction Scheme (with desorbed intermediates) in which the dehydrogenating gallium species are responsible for dehydrogenation of propane, of oligomers and of cyclic olefins and diolefins while protonic sites are responsible for oligomerization, cyclization and cracking. This bifunctional transformation is kinetically limited by propane dehydrogenation. Unfortunately, gallium species also catalyze alkane cracking and hydrogenolysis as well as alkene hydrogenation with formation of the undesired products methane and ethane. From the comparison of the catalytic properties of MFI gallosilicates calcined under air flow at various temperatures, it can be concluded that tetrahedral gallium is inactive in dehydrogenation Reactions. Dehydrogenation occurs through a bifunctional mechanism involving the joint participation of gallium oxide (extra framework species) and of protonic sites. Coke formed during propane aromatization causes a blockage of the access to the protonic sites of the zeolite which is responsible for deactivation. Ga decreases the coking/aromatization rate ratio of HMFI and facilitates the coke removal through oxidative treatment, both effects being more pronounced after Ga/HMFI pretreatment at high temperature under hydrogen because of the better dispersion of the Ga species.
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acylation of phenol with acetic acid over a hzsm5 zeolite Reaction Scheme
Journal of Molecular Catalysis, 1994Co-Authors: Isabel C Neves, Fernando Ramôa Ribeiro, P Magnoux, Francois Jayat, G Perot, Michel Gubelmann, M GuisnetAbstract:Abstract The Scheme of the gas phase phenol acylation with acetic acid on a HZSM5 zeolite was established from the effect of contact time (hence of conversion) on the product distribution. Phenyl acetate and o -hydroxyacetophenone are primary products, O-acylation being much faster than C-acylation. At high conversion, part of the o -hydroxyacetophenone results from the acylation of phenol with phenyl acetate. The formation of p -hydroxyacetophenone which does not occur through phenol acylation involves the hydrolysis of p -acetoxyacetophenone selectively formed through the autoacylation of phenyl acetate. The ortho -selectivity of phenol acylation can be related to a pronounced stabilization of the transition state while the para -selectivity of phenyl acetate autoacylation could be due to a steric hindrance to the approach of the acetyl group in the ortho -position of phenyl acetate.
Julius C. Schuster - One of the best experts on this subject based on the ideXlab platform.
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Liquidus Projection and Reaction Scheme of the Co-Al-Nb System
Journal of Phase Equilibria and Diffusion, 2012Co-Authors: Martin Palm, Oleksandr I. Dovbenko, Frank Stein, Julius C. SchusterAbstract:By metallographic observation of the as-cast microstructures, determination of the liquidus temperatures and the temperatures of invariant Reactions by differential thermal analysis, and measurement of the compositions of the primary phases and the eutectic residuals by electron probe miroanalysis, a liquidus projection for the Co-Al-Nb system has been established for the first time. The binary Co-Nb intermetallic phases have a large solid solubility for Al and their melting temperatures increase markedly by the addition of Al. The only ternary compound, the Heusler phase NbCo2Al, melts incongruently at about 1485 °C. By CALPHAD modelling the consistency of the experimental data has been checked. Calculated and experimentally determined temperatures of the invariant Reactions are in good agreement and are summarised within a Reaction Scheme.
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Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium
Metallurgical and Materials Transactions A, 2009Co-Authors: Hai-lin Chen, F. Weitzer, Nataliya Krendelsberger, Julius C. SchusterAbstract:The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500 °C, and metallography. Solid-state phase equilibria at 900 °C are determined for alloys containing ≤75 at. pct aluminum and at 600 °C for alloys containing >75 at. pct Al. A Reaction Scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for ≤50 at. pct aluminum is dominated by the primary crystallization field of bcc β(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L12-type phase τ forms in a peritectic Reaction pmax at 1393 °C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + α(Ti,Al) = TiAl changes into an eutectic L = α(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition Reactions and ternary peritectics to end in the binary eutectic L = Cr7Al45 + (Al).
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Reaction Scheme and Liquidus Surface in the Al-Rich Section of the Al-Cr-Ni System
Metallurgical and Materials Transactions A, 2008Co-Authors: F. Weitzer, Nataliya Krendelsberger, Wei Xiong, Shuhong Liu, Julius C. SchusterAbstract:The constitution of the ternary system Al-Cr-Ni is investigated over the entire composition range using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDXA), differential thermal analysis (DTA) up to 1500 °C, and metallography. The ternary phase τ1 is confirmed. Its crystal structure, homogeneity range, and melting temperature are corroborated. Two additional ternary phases, labeled τ2 and τ3, are stable at 700 °C. Their compositions are Al77.5Cr12.5Ni10 and Al80Cr15Ni5, respectively. Their XRD powder patterns are shown. The isothermal section at 700 °C and the Reaction Scheme linking it with the liquidus surface are presented. The Al-rich part of the liquidus surface is characterized by an eutectic trough, which descends monotonously from the pseudobinary maximum emax1: L = NiAl + (Cr) at 1433 ± 1 °C through a series of transition Reactions and ends in the ternary eutectic E2: L = Cr7Al45 + NiAl3 + (Al) at 639 °C.
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on the Reaction Scheme and liquidus surface in the ternary system al si ti
International Journal of Materials Research, 2008Co-Authors: Shuhong Liu, Julius C. Schuster, F. Weitzer, Nataliya KrendelsbergerAbstract:Abstract The constitution of the ternary system Al–Si–Ti is reinvestigated over the entire composition range using X-ray diffraction, energy dispersive X-ray analysis, differential thermal analysis up to 1500 °C and metallography. The ternary phases τ1 and τ2 are confirmed and their crystal structures and solid state phase equilibria are corroborated. The compositions observed confirm previous literature. The phase τ1 (I41/amd, Zr3Al4Si5-type) melts incongruently at 953 °C < T < 1000 °C into L + τ2 + TiSi2. The phase τ2 (Cmcm, ZrSi2-type) melts incongruently at 1338 °C into L + TiSi + TiSi2. The liquidus surface is characterized by a eutectic trough, which descends monotonically from the pseudobinary maximum emax1 L = βTi + Ti5Si3 at 1540 ± 5 °C through a series of transition Reactions and ends in the ternary eutectic L = τ1 + (Si) + (Al) at 573 °C.
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On the Reaction Scheme and Liquidus Surface in the Ternary System Al-Fe-Si
Metallurgical and Materials Transactions A, 2007Co-Authors: Nataliya Krendelsberger, F. Weitzer, Julius C. SchusterAbstract:The constitution of the ternary system Al-Fe-Si is reinvestigated over the entire composition range by X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy/energy dispersive X-ray (SEM/EDX). The liquidus projection obtained shows equilibria among nine ternary phases. Except for the occurrence of the three additional ternary phases not recognized at the time, the previous work is found to be accurate in most details. In the isothermal section at 550 °C, an additional ternary phase occurs for which the indexed X-ray powder diffraction pattern is presented. Crystal structures reported for the other phases are all confirmed.
Xenophon E Verykios - One of the best experts on this subject based on the ideXlab platform.
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partial oxidation of methane to synthesis gas via the direct Reaction Scheme over ru tio2 catalyst
Catalysis Letters, 1996Co-Authors: Yiannis Boucouvalas, Zhaolong Zhang, Xenophon E VerykiosAbstract:The partial oxidation of methane to synthesis gas has been investigated over various supported metal catalysts. The effects of operational variables on mass and heat transport resistances were investigated for defining the kinetic regime. It is observed that, in the absence of significant mass and heat transfer resistances, high selectivity (up to 65%) to synthesis gas is obtained over Ru/TiO2 catalysts in the low methane conversion range (\(X_{O_2 }< 100\% \)) whereas only negligibly small selectivity to synthesis gas is observed over all other catalysts investigated under similar conditions. This indicates that the Ru/TiO2 catalyst possesses unique properties, offering high selectivity to synthesis gas formation via the direct Reaction Scheme, whereas the other catalysts promote the sequence of total oxidation of methane to CO2 and H2O, followed by reforming Reactions to synthesis gas. An increase of selectivity to synthesis gas, in the presence of oxygen, is achieved over the Ru/TiO2 catalyst by multi-feeding oxygen, which is attributed to suppression of deep oxidation of H2 and CO.
Andrew Rutter - One of the best experts on this subject based on the ideXlab platform.
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Mixing Performance Evaluation for Commercially Available Micromixers Using Villermaux–Dushman Reaction Scheme with the Interaction by Exchange with the Mean Model
Organic Process Research & Development, 2017Co-Authors: Joseph M. Reckamp, Ashira Bindels, Sophie Duffield, Yangmu Chloe Liu, Eric Bradford, Eric M. Ricci, Flavien Susanne, Andrew RutterAbstract:The development of low-volume continuous processes for the pharmaceutical industry requires a greater understanding of mixing in microreactors. In this paper, numerous commercially available micromixers are evaluated using the Villermaux–Dushman Reaction Scheme and the interaction by exchange with the mean (IEM) mixing model to quantify the mixing time. The work presents the mixing times as a function of flow rate and energy dissipation for mixers including T-mixers, Ehrfeld Mikrotechnik BTS micromixers, and Syrris Asia microchips.
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mixing performance evaluation for commercially available micromixers using villermaux dushman Reaction Scheme with the interaction by exchange with the mean model
Organic Process Research & Development, 2017Co-Authors: Joseph M. Reckamp, Ashira Bindels, Sophie Duffield, Yangmu Chloe Liu, Eric Bradford, Flavien Susanne, Eric Ricci, Andrew RutterAbstract:The development of low-volume continuous processes for the pharmaceutical industry requires a greater understanding of mixing in microreactors. In this paper, numerous commercially available micromixers are evaluated using the Villermaux–Dushman Reaction Scheme and the interaction by exchange with the mean (IEM) mixing model to quantify the mixing time. The work presents the mixing times as a function of flow rate and energy dissipation for mixers including T-mixers, Ehrfeld Mikrotechnik BTS micromixers, and Syrris Asia microchips.
Yiannis Boucouvalas - One of the best experts on this subject based on the ideXlab platform.
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partial oxidation of methane to synthesis gas via the direct Reaction Scheme over ru tio2 catalyst
Catalysis Letters, 1996Co-Authors: Yiannis Boucouvalas, Zhaolong Zhang, Xenophon E VerykiosAbstract:The partial oxidation of methane to synthesis gas has been investigated over various supported metal catalysts. The effects of operational variables on mass and heat transport resistances were investigated for defining the kinetic regime. It is observed that, in the absence of significant mass and heat transfer resistances, high selectivity (up to 65%) to synthesis gas is obtained over Ru/TiO2 catalysts in the low methane conversion range (\(X_{O_2 }< 100\% \)) whereas only negligibly small selectivity to synthesis gas is observed over all other catalysts investigated under similar conditions. This indicates that the Ru/TiO2 catalyst possesses unique properties, offering high selectivity to synthesis gas formation via the direct Reaction Scheme, whereas the other catalysts promote the sequence of total oxidation of methane to CO2 and H2O, followed by reforming Reactions to synthesis gas. An increase of selectivity to synthesis gas, in the presence of oxygen, is achieved over the Ru/TiO2 catalyst by multi-feeding oxygen, which is attributed to suppression of deep oxidation of H2 and CO.
