scholarly journals Hydrogenation of alkynyl substituted aromatics over rhodium/silica

2021 ◽  
Author(s):  
Joseph W. Gregory ◽  
S. David Jackson
Keyword(s):  
Cascade Reactions ◽  
Activation Energies ◽  
Competitive Reaction ◽  
Fresh Catalyst ◽  
Hydrogen Flux ◽  
Rate Determining Step ◽  
Surface Hydrogen ◽  
Alkyne Hydrogenation ◽  
Competitive Hydrogenation ◽  
Styrene Hydrogenation

AbstractThe cascade reactions of phenylacetylene to ethylcyclohexane and 1-phenyl-1-propyne to propylcyclohexane were studied individually, under deuterium and competitively at 343 K and 3 barg pressure over a Rh/silica catalyst. Both systems gave similar activation energies for alkyne hydrogenation (56 ± 4 kJ mol−1 for phenylacetylene and 50 ± 4 kJ mol−1 for 1-phenyl-1-propyne). Over fresh catalyst the order of reactivity was styrene > phenylacetylene ≫ ethylbenzene. Whereas with the cascade hydrogenation starting with phenylacetylene, styrene hydrogenated much slower phenylacetylene even once all the phenylacetylene was hydrogenated. The activity of ethylbenzene was also reduced in the cascade reaction and after styrene hydrogenation. These reductions in rate were likely due to carbon laydown from phenylacetylene and styrene. Similar behavior was observed with the 1-phenyl-1-propyne cascade. Deuterium experiments revealed similar positive KIEs for phenylacetylene (2.6) and 1-phenyl-1-propyne (2.1). Ethylbenzene hydrogenation/deuteration gave a KIE of 1.6 obtained after styrene hydrogenation in contrast to the inverse KIE of 0.4 found with ethylbenzene hydrogenation/deuteration over a fresh catalyst, indicating a change in rate determining step. Competitive hydrogenation between phenylacetylene and styrene reduced the rate of phenylacetylene hydrogenation but increased selectivity to ethylbenzene suggesting a change in the flux of sub-surface hydrogen. In the competitive reaction between 1-phenyl-1-propyne and propylbenzene, the rate of hydrogenation of 1-phenyl-1-propyne was increased and the rate of alkene isomerization was decreased, likely due to an increase in the hydrogen flux for hydrogenation and a decrease in the hydrogen species active in methylstyrene isomerization.

Investigation of the Energetics of the Reactions of NH2 Species with Hydrogen and NO on the Pt(100) Surface by the Method of UBI-QEP

2003 ◽  
Vol 10 (04) ◽  
pp. 585-590 ◽  
Author(s):  
S. Azizian ◽  
H. Iloukhani
Keyword(s):  
Activation Energy ◽  
Surface Reaction ◽  
Activation Energies ◽  
Water Production ◽  
Exponential Potential ◽  
Bond Index ◽  
Rate Determining Step ◽  
Experimental Findings ◽  
Energy Of Formation

The formation of NH 2, ads and its further reactions with hydrogen and NO on the Pt(100) surface were previously studied by the methods of HREELS and TPR, in order to understand the role of amino species in the mechanism of the NO + H 2 reaction. In this work the method of unity bond index – quadratic exponential potential (UBI-QEP) has been employed to rationalize the experimental findings by calculating the energies associated with the envisaged routes of reactions. It is concluded that the activation energy of formation of NH 2, ads is higher than water production. The simplicity of recombinative desorption of N2 is due to the decrease of its activation energy because of the destabilizing effect of O ads and NO ads. The rate-determining step of explosive surface reaction in the saturated coadsorption layer of NH 2, ads and NOads is dissociation of NO ads. Autocatalytic acceleration of the explosive reactions is due to the decrease of activation energy of the rds by increasing the number adsorption vacant sites. H 2 O is produced via two different processes with different activation energies. NH 3 is produced via several paths.

Dissolution of organic solvents from painted surfaces into water

2000 ◽  
Vol 78 (4) ◽  
pp. 464-473 ◽  
Author(s):  
J C Wren ◽  
D J Jobe ◽  
G G Sanipelli ◽  
J M Ball
Keyword(s):  
Organic Compounds ◽  
Organic Solvents ◽  
Nuclear Reactor ◽  
Dissolution Kinetics ◽  
Activation Energies ◽  
Dissolution Mechanism ◽  
Rate Determining Step ◽  
Organic Impurities ◽  
Accident Conditions ◽  
Reactor Accidents

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents.

High-temperature oxidation of ion-plated TiN and TiAlN films

1993 ◽  
Vol 8 (5) ◽  
pp. 1093-1100 ◽  
Author(s):  
Hiroshi Ichimura ◽  
Atsuo Kawana
Keyword(s):  
High Temperature ◽  
Oxidation Rate ◽  
High Temperature Oxidation ◽  
Mass Gain ◽  
Activation Energies ◽  
Ion Diffusion ◽  
Temperature Oxidation ◽  
Al Content ◽  
Rate Determining Step ◽  
Apparent Activation Energies

The high-temperature oxidation of TiN, Ti0.9Al0.1N, and Ti0.6Al0.4N films which were deposited onto stainless steel substrates using an arc ion-plating apparatus was studied at temperatures ranging from 923 to 1173 K for 0.6 to 60 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. From their temperature dependence, the apparent activation energies of oxidation were determined. With increasing Al contents, the oxidation rate decreased, and the activation energies of oxidation reaction increased. Formed oxide layers were analyzed by XRD, SEM, and EPMA. With increased Al content in TiAlN films, the rate-determining step changes from oxygen ion diffusion in formed rutile to oxygen or aluminum ion diffusion in the formed Al2O3 layer.

scholarly journals Effect of Alkali Metal Ions on the Formation Mechanism of HCN During Pyridine Pyrolysis

2020 ◽  
Author(s):  
Ji Liu ◽  
Wei Zhao ◽  
Xin-rui Fan ◽  
Ming-xin Xu ◽  
Shu Zheng ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Density Functional ◽  
Hydrogen Transfer ◽  
Activation Energies ◽  
Alkali Metal Ions ◽  
Coal Pyrolysis ◽  
Pyrolysis Mechanism ◽  
Rate Determining Step ◽  
Calculation Results

Abstract The present work aims at the effects of alkali metal ions (Na+, K+) on the NOx precursor formation during coal pyrolysis by employing the N-containing pyridine as the model compound. Density functional theory (DFT) calculations were used to elucidate the pyridine pyrolysis mechanism and pathways for the HCN formation. The calculation results indicate that Na+ and K+ have distinct influences on different pyrolysis reactions. The two alkali metal ions can facilitate the initial hydrogen transfer from C1 to N and C2, while it is the opposite situation for other hydrogen migration reactions. Both Na+ and K+ significantly reduce the activation energies for the C-C bond breakage and the formation of the triple bond, whereas the activation energies are increased for isomerization reactions. The two alkali metal ions modulate the rate-determining step of the pyrolysis process and promote the formation of HCN from pyridine by decreasing the activation energies of the rate-determining steps in different pathways.

ONE-DIMENSIONAL CHAOTIC LAMINAR FLOW WITH COMPETITIVE EXOTHERMIC AND ENDOTHERMIC REACTIONS

2020 ◽  
pp. 1-23
Author(s):  
S. D. WATT ◽  
Z. HUANG ◽  
H. S. SIDHU ◽  
A. C. MCINTOSH ◽  
J. BRINDLEY
Keyword(s):  
Laminar Flow ◽  
Numerical Solution ◽  
Strong Dependence ◽  
Activation Energies ◽  
Steady States ◽  
Chaotic Advection ◽  
Competitive Reaction ◽  
One Dimensional ◽  
Reaction Fronts ◽  
Endothermic Reactions

We consider the numerical solution of competitive exothermic and endothermic reactions in the presence of a chaotic advection flow. The resulting behaviour is characterized by a strong dependence on the competitive reaction history. The burnt temperature is not immediately connected to simple enthalpy calculations, so there is a subtlety in the interplay between the major parameters, notably the Damköhler number, the ratio of the heats of exothermic and endothermic reactions, as well as the ratio of their respective activation energies. This paper seeks to explore the way these parameters affect the steady states of these reaction fronts and their stability.

The catalytic fission of the carbon-nitrogen bond II. The reactions of ethylamine and hydrogen on evaporated metal films

1958 ◽  
Vol 244 (1238) ◽  
pp. 398-410 ◽  
Keyword(s):  
Pressure Dependence ◽  
Reaction Mechanisms ◽  
Metal Films ◽  
Activation Energies ◽  
Effect Of Temperature ◽  
Gold Films ◽  
Rate Determining Step ◽  
The Common ◽  
Nitrogen Bond ◽  
And Tungsten

The catalytic fission of the C—N bond of ethylamine in hydrogen led to two main reactions: platinum films favoured reaction I, to ammonia and ethane; nickel, palladium and gold films favoured reaction II, producing ammonia and diethylamine and also triethylamine by further reaction of the first products. Both types of reaction occurred on rhodium and tungsten films. The effect of temperature was studied and the values of the activation energies indicated that the fission of the C—N bond was the common rate-determining step for the various pro­cesses. Increase of pressure of ethylamine caused reaction II to occur on platinum films and eventually to predominate over reaction I. Although the rate of fission of the C—N bond on platinum was not influenced by the pressure of ethylamine, the ratio of the rates of reaction II and I depended on the second power of this pressure. Reaction mechanisms are discussed and the pressure dependence of the rates on platinum considered in terms of differing types of adsorption of the amine. The activity of the various catalysts is compared and discussed with regard to their ability to break the C—N bond in ethylamine. It was found that ethylamine was more easily decomposed than methylamine on all the metals which were common to this investigation and to the previous work on the decomposition of methylamine.

Studies of the variations in bond dissociation energies of aromatic compounds. I. Mono-bromo-aryles

1953 ◽  
Vol 219 (1138) ◽  
pp. 341-352 ◽  
Keyword(s):  
Hydrogen Bromide ◽  
Heat Of Formation ◽  
Activation Energies ◽  
Bond Dissociation Energies ◽  
First Order ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Aromatic Radicals

Investigation of the pyrolyses of bromobenzene, β -bromonaphthalene, α -bromonaphthalene, 9-bromophenanthrene and 9-bromoanthraeene in the presence of an excess of toluene has shown that reaction (1) Ar .Br → Ar • + Br (1) is the primary and rate-determining step of the pyrolysis. The progress of reaction was measured by the rate of formation of hydrogen bromide, and it was shown that this rate obeys first-order kinetics. The following values were obtained for the activation energies and frequency factors of unimolecular decompositions represented by equation (1): compound E (kcal/mole) 10 -13 v (sec -1 ) bromobenzene 70.9 2 β -bromonaphthalene 700 1.5 α -bromonaphthalene 70.9 3.5 9-bromophenanthrene 67.7 1 9-bromoanthracene 65.6 1.5 Assuming that recombination of bromine atoms with aromatic radicals does not involve any activation energy we conclude tha t the determined activation energies correspond to the respective C—Br bond dissociation energies. The effect of molecular structure on the C—Br bond dissociation energy is discussed. The heat of formation of the phenyl radical is determined, and this result is used for calculating the various Ph — X bond dissociation energies.

Effects of Provocation on Emotions and Aggression: An Experimental Study with Aggressive Children

2006 ◽  
Vol 65 (2) ◽  
pp. 117-124 ◽  
Author(s):  
Christina Stadler ◽  
Sonja Rohrmann ◽  
Sibylle Steuber ◽  
Fritz Poustka
Keyword(s):  
Experimental Study ◽  
Positive Emotions ◽  
Skin Conductance Level ◽  
Physiological Measures ◽  
Competitive Reaction ◽  
Experimental Conditions ◽  
Conduct Disordered ◽  
Physiological Variables ◽  
Aggressive Children ◽  
Conductance Level

In this study, the effects of an experimental-induced provocation on emotions and aggression were examined in 34 aggressive conduct-disordered children using a competitive reaction time paradigm. Two experimental conditions were created, an increasing provocation and a low constant provocation condition. Self-rated anger was assessed directly after provocation on a 5-point-visual scale. In addition, negative and positive emotions as well as physiological measures (heart rate and skin conductance level) were measured at baseline and after provocation. Results revealed that participants’ aggressive behaviour and subjective emotions differed as a function of the opponent’s level of provocation. Concerning physiological parameters, no significant differences were found between the experimental conditions. These results suggest that affective, but not physiological variables characterize reactive aggression in conduct-disordered children.

Deep level study in epitaxial 4H-SiC grown on substrates inclined toward

2002 ◽  
Vol 719 ◽  
Author(s):  
Masashi Kato ◽  
Masaya Ichimura ◽  
Eisuke Arai ◽  
Shigehiro Nishino
Keyword(s):  
Deep Level Transient Spectroscopy ◽  
Deep Level ◽  
Activation Energies ◽  
Thickness Dependence ◽  
Epitaxial Layers ◽  
Transient Spectroscopy

AbstractEpitaxial layers of 4H-SiC are grown on (0001) substrates inclined toward <1120> and <1100> directions. Defects in these films are characterized by deep level transient spectroscopy (DLTS) in order to clarify the dependence of concentrations and activation energies on substrate inclination. DLTS results show no such dependence on substrate inclination but show thickness dependence of the concentration.

Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

2019 ◽  
Author(s):  
Raghu Nath Dhital ◽  
keigo nomura ◽  
Yoshinori Sato ◽  
Setsiri Haesuwannakij ◽  
Masahiro Ehara ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Dft Calculations ◽  
Bond Activation ◽  
Mild Conditions ◽  
Selective Transformation ◽  
Rate Determining Step ◽  
Highly Active ◽  
Harsh Conditions ◽  
Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the <i>beta</i>-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

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