Kinetics and Mechanism of Hydrogenolyses. The Addition of Hydrogen Atoms to Propylene, Toluene, and Xylene

Benson, S. W.; Shaw, Robert

doi:10.1063/1.1701575

Cited by 37 publications

(7 citation statements)

References 20 publications

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“…The observed rate law for HME-induced biphenyl hydrogenolysis is therefore described by eq 1. This rate law is consistent with a chain transfer occurring almost entirely through the reaction of phenyl radical with molecular hydrogen and is similar in form to that described by Benson for toluene hydrogenolysis …”

Section: Resultssupporting

confidence: 88%

Hydrogen Transfer Induced Cleavage of Biaryl Bonds

et al. 1997

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Biaryl bonds are the strongest carbon−carbon single bonds in fossil fuels. This paper examines hydrogenolysis and alkane cohydrogenolysis of biphenyl and dimethylbiphenyls, in detail. Biphenyl cleavage was found to be enhanced by copyrolysis and cohydrogenolysis with small amounts of 2,2,3,3-tetramethylbutane (hexamethylethane, HME). Much smaller enhancements were found for cohydrogenolysis with other alkanes. Increased biaryl cleavage rates, in HME cohydrogenolysis, were found to be a direct consequence of initiation by hydrogen atom generated during HME decomposition. Both biphenyl pyrolysis and hydrogenolysis mechanisms involve ipso hydrogen atom attack, followed by ejection of phenyl radical and the formation of benzene. Hydrogen atom is regenerated either through the phenylation of starting biphenyl or through the direct reaction of phenyl radical with H2. Both propagation reactions are very fast, leading to highly efficient chain transfer. Biaryl bond hydrogenolysis was found to be first-order in biphenyl and half-order in H2. Dimethylbiphenyls were found to undergo both demethylation and biaryl cleavage reactions during either neat hydrogenolysis or HME cohydrogenolysis. Cleavage of the much weaker aromatic methyl bond was found to be only slightly favored over biaryl cleavage in dimethylbiphenyl/HME cohydrogenolysis. The branching ratio for biaryl cleavage versus demethylation was also found to be sensitive to dimethylbiphenyl structure. The similar rates for biaryl cleavage and demethylation, as well as the structure sensitivity of the branching ratio, indicate the rate of formation and stability of the ipso hydrogen atom adduct are important in determining the rates of aromatic displacement reactions.

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Section: Resultssupporting

confidence: 88%

Hydrogen Transfer Induced Cleavage of Biaryl Bonds

et al. 1997

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“…These global reactions showed excellent agreement with experimental rate constants at temperatures lower than about 1000 K [6], a temperature similar to that of our CVD reactor, justifying the use of the simple reaction mechanism in our model. The exhaust-gas analyses of our reactor [4] also support the reaction mechanism.…”

Section: Gas-phase Reactionssupporting

confidence: 78%

Simple Estimation of Nanoparticle Diameter Produced in a Flow Tube Reactor

Kuwana

Saito

2005

MRS Proc.

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In many carbon nanotube synthesis methods, catalyst nanoparticles are formed via pyrolysis of a precursor such as ferrocene. Since the diameter of a carbon nanotube is usually determined by the diameter of the catalyst nanoparticle, it is of great importance to control the size of nanoparticles. To do so, it is necessary to identify the key reaction parameters that influence nanoparticle size. For engineering purposes, a simple analytical model offers a convenient first estimation of particle diameter. It also clarifies the dependence of nanoparticle diameter on each reaction parameter and enhances our understanding of the formation mechanism of nanoparticles. This paper presents a simplified model that can calculate the diameter of particles and the model's analytical solutions.Mater. Res. Soc. Symp. Proc. Vol. 900E

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“…[14][15][16][17][18][19] The high synthesis temperatures are mainly due to the strong CÀC bond strength in aromatic rings and that of R-CH 3 (R corresponds to an aromatic ring, $434.7 kJ mol À1 in toluene). [20] Unfortunately, the high synthesis temperatures used result in low production rates of the CNTs, as well as a high concentration of benzene residue in the reactor. The CNT diameters vary from several nanometers to more than 100 nanometers.…”

Section: Introductionmentioning

confidence: 99%

Acetylene‐Enhanced Growth of Carbon Nanotubes on Ceramic Microparticles for Multi‐Scale Hybrid Structures

He¹,

Bai²

2011

Chemical Vapor Deposition

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A mixture of acetylene and xylene is used as the carbon source to directly synthesize carbon nanotube (CNT)/alumina (Al 2 O 3 ) microsphere hybrid structures by CVD. The hybrid structures are modulated by varying the acetylene ratio and reactor temperature. The addition of acetylene can significantly improve the CNT growth rate on Al 2 O 3 at temperatures lower than 600 8C. A tenfold improvement in CNT growth rate is obtained at 550 8C when only 2 vol.-% acetylene is added. Meanwhile, acetylene favors the formation of bundles containing high-density CNTs. The increase in the temperature promotes the formation of CNTs with large diameters and low number density. Mass spectrometry (MS) is used to investigate the decomposition of a mixture of acetylene/xylene at temperatures ranging from 450 to 700 8C, under the experimental conditions used. Acetylene decomposes with an increasing rate with temperature from 450 8C, however notable decomposition of xylene is not detected below 700 8C, which corresponds to the formation of the CNTs of varied diameters. This study demonstrates the possibility of large-scale production of desired nano/micrometer multifunctional CNT/Al 2 O 3 hybrid fillers using a gas/liquid mixed carbon source.

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Kinetics and Mechanism of Hydrogenolyses. The Addition of Hydrogen Atoms to Propylene, Toluene, and Xylene

Cited by 37 publications

References 20 publications

Hydrogen Transfer Induced Cleavage of Biaryl Bonds

Hydrogen Transfer Induced Cleavage of Biaryl Bonds

Simple Estimation of Nanoparticle Diameter Produced in a Flow Tube Reactor

Acetylene‐Enhanced Growth of Carbon Nanotubes on Ceramic Microparticles for Multi‐Scale Hybrid Structures

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