Adsorption and Reaction on Thin Metal Overlayers

1986 ◽  
Vol 83 ◽  
Author(s):  
Paul J. Berlowitz ◽  
Charles H. F. Peden ◽  
D. Wayne Goodman
Keyword(s):  
Bimetallic Catalysts ◽  
Metallic Films ◽  
Kinetic Measurements ◽  
Unique Character ◽  
Cyclohexane Dehydrogenation ◽  
Adsorption Of Co ◽  
Dehydrogenation Reactions ◽  
Temperature Programmed ◽  
Metal Overlayers ◽  
Kinetics Of

ABSTRACTThese studies have addressed the adsorption of CO on very thin (submonolayer to multilayer) deposits of Cu, Ni, Pd, and Fe on single crystals of Ru and W. The kinetics of the methanation, ethane hydrogenolysis, and cyclohexane dehydrogenation reactions have also been measured over these model bimetallic catalysts. Temperature programmed desorption (TPD) spectra of CO at submonolayer coverages reveal new desorption features which have significantly perturbed peak maxima from those observed on the bulk metals, indicating the unique character of these monolayer metallic films. This behavior has been correlated with LEED, ARUPS, work function, and kinetic measurements.

Kinetics of temperature-programmed reactivation of a hydrodesulphurization catalyst

1983 ◽  
Vol 48 (12) ◽  
pp. 3340-3355 ◽  
Author(s):  
Pavel Fott ◽  
Pavel Šebesta
Keyword(s):  
Carbon Dioxide ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Thin Layer ◽  
Kinetic Parameters ◽  
Diffusion Region ◽  
Reaction Heat ◽  
Gaseous Products ◽  
Temperature Programmed ◽  
Kinetics Of

The kinetic parameters of reactivation of a carbonized hydrodesulphurization (HDS) catalyst by air were evaluated from combined thermogravimetric (TG) and differential thermal analysis (DTA) data. In addition, the gaseous products leaving a temperature-programmed reactor with a thin layer of catalyst were analyzed chromatographically. Two exothermic processes were found to take part in the reactivation, and their kinetics were described by 1st order equations. In the first process (180-400 °C), sulphur in Co and Mo sulphides is oxidized to sulphur dioxide; in the second process (300-540 °C), in which the essential portion of heat is produced, the deposited carbon is oxidized to give predominantly carbon dioxide. If the reaction heat is not removed efficiently enough, ignition of the catalyst takes place, which is associated with a transition to the diffusion region. The application of the obtained kinetic parameters to modelling a temperature-programmed reactivation is illustrated on the case of a single particle.

scholarly journals Determining the mass-related reaction effectiveness factor of large, nonspherical fuel particles for bridging between intrinsic and apparent combustion kinetics

2019 ◽  
Vol 141 (2) ◽  
pp. 797-806 ◽  
Author(s):  
Tibor Szűcs ◽  
Pal Szentannai
Keyword(s):  
Combustion Process ◽  
Effectiveness Factor ◽  
Cfd Modeling ◽  
Combustion Kinetics ◽  
Kinetic Measurements ◽  
Environmental Requirements ◽  
Fuel Particles ◽  
Related Reaction ◽  
Kinetics Of ◽  
Internal Pore

AbstractThe utilization of challenging solid fuels in the energy industry is urged by environmental requirements. The combustion kinetics of these fuel particles differs markedly from that of pulverized coal, mainly because of their larger sizes, irregular (nonspherical) shapes, and versatile internal pore structures. Although the intrinsic reaction kinetic measurements on very small amounts of finely ground samples of these particles are mostly available, a bridge toward their apparent reaction modeling is not evident. In this study, a method is introduced to build this bridge, the goodness of which was proved on the example of an industrially relevant biofuel. To do this, the results of a macroscopic combustion measurement with real samples in a well-modelable environment have to be used, and for considering some not negligible effects, 3D CFD modeling of the experimental environment is also to be applied. The outcome is the mass-related reaction effectiveness factor as a function of the rate of conversion. This variable can be considered as the active fraction of the entire particle mass on its periphery, and it can be used as the crucial element in modeling the combustion process of the same particle under other circumstances by including the actual boundary conditions. Another advantage of this method is its covering inherently the entire combustion process (water and volatile release, and char combustion) and also its applicability for reactors utilizing bigger particles like fluidized bed combustors.

scholarly journals CO oxidation over Pt-modified CuO catalysts in the presence of water vapour and SO2

2015 ◽  
Vol 18 (2) ◽  
pp. 187-196
Author(s):  
Tri Nguyen ◽  
Anh Cam Ha ◽  
Loc Cam Luu ◽  
Cuong Tien Hoang ◽  
Thi Thi Yen Trinh ◽  
...  
Keyword(s):  
Co Oxidation ◽  
Water Vapour ◽  
Co Adsorption ◽  
X Ray Diffraction ◽  
Active Centers ◽  
Highly Active ◽  
Transmission Electron ◽  
Physico Chemical ◽  
Adsorption Of Co ◽  
Temperature Programmed

The optimal Pt-modified CuO supported on γ-Al2O3 and γ-Al2O3 + CeO2 catalysts have been prepared. Physico-chemical characteristics of catalysts were investigated and determined by the methods of N2 adsorption (BET), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and hydrogen pulse chemisorption (HPC). The characteristics of carbon monoxide (CO) adsorption on catalysts were defined by the method of infrared spectroscopy (IR) in the range of 4000 – 400 cm-1. The effect of the mixture of water vapour and SO2 on the activity of these catalysts for the CO oxidation was assessed. Reactions were conducted at 200oC and 350oC in the absence and presence of the mixture of water vapour (1.1 mol %) and SO2 (0.0625 mol %). Concentrations of O2 and CO in the gas mixture were 9.2 mol % and 0.5 mol %, respectively. The results showed that in the catalysts there exist highly active centers Cu1+ and Pt2+. On the catalysts the adsorption of CO on Cu2+, Pt2+, CeO2, and γ - Al2O3 centres was observed. Addition of CeO2 led to increase the reductivity, CO adsorption but decrease in specific surface area of catalyst. The result PtCu/CeAl catalyst shown higher active, but lower stability compared to PtCu/Al catalyst. The mixture of water vapour and SO2 showed the reversible poisoning toward the Pt-CuO catalysts at a temperature of 350oC, but irreversible at 200oC

Insights into the Kinetics of Cracking and Dehydrogenation Reactions of Light Alkanes in H-MFI

2013 ◽  
Vol 117 (24) ◽  
pp. 12600-12611 ◽  
Author(s):  
Shaama Mallikarjun Sharada ◽  
Paul M. Zimmerman ◽  
Alexis T. Bell ◽  
Martin Head-Gordon
Keyword(s):  
Light Alkanes ◽  
Dehydrogenation Reactions ◽  
Kinetics Of

scholarly journals Mechanism of the 2,3-diphosphoglycerate-dependent phosphoglycerate mutase from rabbit muscle

1972 ◽  
Vol 130 (2) ◽  
pp. 397-410 ◽  
Author(s):  
H. G. Britton ◽  
J. B. Clarke
Keyword(s):  
Chemical Equilibrium ◽  
Phosphoglycerate Mutase ◽  
Rabbit Muscle ◽  
Kinetic Measurements ◽  
Rate Limiting Step ◽  
Ping Pong ◽  
Sequential Mechanism ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Intramolecular Transfer

1. The properties and kinetics of the 2,3-diphosphoglycerate-dependent phosphoglycerate mutases are discussed. There are at least three possible mechanisms for the reaction: (i) a phosphoenzyme (Ping Pong) mechanism; (ii) an intermolecular transfer of phosphate from 2,3-diphosphoglycerate to the substrates (sequential mechanism); (iii) an intramolecular transfer of phosphate. It is concluded that these mechanisms cannot be distinguished by conventional kinetic measurements. 2. The fluxes for the different mechanisms are calculated and it is shown that it should be possible to distinguish between the mechanisms by appropriate induced-transport tests and by comparing the fluxes of 32P- and 14C-labelled substrates at chemical equilibrium. 3. With 14C-labelled substrates no induced transport was found over a wide concentration range, and with 32P-labelled substrates co-transport occurred that was independent of concentration over a twofold range. 14C-labelled substrates exchange at twice the rate of 32P-labelled substrates at chemical equilibrium. The results were completely in accord with a phosphoenzyme mechanism and indicated a rate constant for the isomerization of the phosphoenzyme of not less than 4×106s−1. The intramolecular transfer of phosphate (and intermolecular transfer between two or more molecules of substrate) were completely excluded. The intermolecular transfer of phosphate from 2,3-diphosphoglycerate would have been compatible with the results only if the Km for 2-phosphoglycerate had been over 7.5-fold smaller than the observed value and if an isomerization of the enzyme-2,3-diphosphoglycerate complex had been the major rate-limiting step in the reaction. 4. The very rapid isomerization of the phosphoenzyme that the experiments demonstrate suggests a mechanism that does not involve a formal isomerization. According to this new scheme the enzyme is closely related mechanistically and perhaps evolutionarily to a 2,3-diphosphoglycerate diphosphatase.

The Dehydrogenation Reactions and Kinetics of 2LiBH4−Al Composite

2009 ◽  
Vol 113 (42) ◽  
pp. 18424-18430 ◽  
Author(s):  
Yao Zhang ◽  
Qifeng Tian ◽  
Jian Zhang ◽  
Shu-Sheng Liu ◽  
Li-Xian Sun
Keyword(s):  
Al Composite ◽  
Dehydrogenation Reactions ◽  
Kinetics Of

Kinetics of the anionic coordination dimerization of isoprene

1982 ◽  
Vol 47 (2) ◽  
pp. 594-602 ◽  
Author(s):  
Jan Bartoň ◽  
Miroslav Kašpar ◽  
Vlastimil Růžička
Keyword(s):  
Kinetic Model ◽  
Time Dependence ◽  
Kinetic Measurements ◽  
Parameter Equation ◽  
Kinetics Of ◽  
Two Parameter

The kinetics of the anionic coordination dimerization of isoprene (i.e., 2-methyl-1,3-butadiene) to β-myrcene (i.e., 7-methyl-3-methylene-1,6-octadiene) was investigated. The reaction was initiated with sodium in the presence of dicyclohexyl amine in tetrahydrofuran. Kinetic measurements showed that ionic pairs of isoprenyl sodium were additionally solvated by two molecules of tetrahydrofuran. A kinetic model of the reaction enabled the time dependence of the isoprene concentration to be expressed in terms of a two-parameter equation.

Picosecond Optical Second Harmonic Studies of Adsorbate Reduction Kinetics on Cadmium Sulfide

1993 ◽  
Vol 334 ◽  
Author(s):  
T. W. Scott ◽  
J. Martorell ◽  
Y. J. Chang
Keyword(s):  
Cadmium Sulfide ◽  
Near Infrared ◽  
Transient Absorption ◽  
Second Harmonic ◽  
Harmonic Signal ◽  
Recombination Luminescence ◽  
Kinetic Measurements ◽  
Time Resolved ◽  
Sum Frequency ◽  
Kinetics Of

AbstractTime resolved surface second harmonic generation has been used to probe the photoreduction kinetics of malachite green adsorbed onto single crystal cadmium sulfide. A detailed analysis is presented of how the adsorbates and the noncentrosymmetric substrate contribute separately to the total second harmonic signal. Conditions under which the adsorbates can be cleanly detected are described. To complement kinetic measurements of adsorbate reduction, the time evolution of conduction band carriers was determined using sum frequency up conversion of the recombination luminescence. In addition, the formation and decay of surface trapped carriers was monitored using near infrared transient absorption. Comparing the time scale for photoreduction with the relaxation kinetics of mobile and trapped charge carriers indicates that short lived mobile carriers rather than longer lived surface trapped carriers dominate interfacial charge transfer in this system.

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