Kinetics Of Catalytic Reactions Research Articles

Reaction of 4-amino-4′-methoxydiphenylamine oxidation in surfactant solutions

The kinetics of noncatalytic and catalytic oxidation reactions of 4-amino-4′-methoxydiphenylamine with different oxidants in aqueous solutions and in the presence of surfactants was studied. The catalytic activity of iridium(IV) in this reaction in weakly acidic solutions (pH = 3) was estimated. The dependences of the rates of noncatalytic and catalytic processes on the component concentrations in the reaction mixture, the acidity of solutions, and their temperature were determined. A method for the catalimetric determination of iridium(IV) was proposed and verified against model mixtures.

Facile “Green” Synthesis, Characterization, and Catalytic Function of β‐D‐Glucose‐Stabilized Au Nanocrystals

We present a straightforward, economically viable, and "green" approach for the synthesis and stabilization of relatively monodisperse Au nanocrystals with an average diameter of 8.2 nm (standard deviation, SD=2.3 nm) by using nontoxic and renewable biochemical of beta-D-glucose and by simply adjusting the pH environment in aqueous medium. The beta-D-glucose acts both as reducing agent and capping agent for the synthesis and stabilization of Au nanocrystals in the system. The UV/Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), electron diffraction (ED), and X-ray diffraction (XRD) techniques were employed to systematically characterize Au nanocrystals synthesized. Additionally, it is shown that these beta-D-glucose-stabilized Au nanocrystals function as effective catalyst for the reduction of 4-nitrophenol in the presence of NaBH4 (otherwise unfeasible if only the strong reducing agent NaBH4 is employed), which was reflected by the UV/Vis spectra of the catalytic reaction kinetics.

Determination of kinetic parameters of the oxidehydrogenation of ethane with CO 2 on nanosized calcium-doped ceria under fast deactivation processes

Abstract Kinetic parameters of the oxidehydrogenation of ethane with CO 2 on nanosized Ca-doped CeO 2 have been investigated. During reaction, interaction of the reactants with the oxide catalyst causes a fast deactivation process. Overlapping of this fast deactivation with catalytic reaction makes quite difficult the reliable determination of kinetic parameters. This handicap can be overcome by getting sufficient data in a short testing time, thus reducing the degree of deactivation. The kinetics of catalytic reaction and of catalyst deactivation have been studied by conducting a series of consecutive tests at increasing temperatures in steps of 20 °C and monitoring the evolution of the reaction for periods of 30 min on stream at each temperature, with full product analysis every 3 min. At temperatures above 680 °C, catalytic rates decreased linearly with run time at isothermal operation, while deactivation rates increased with increasing temperature. Analysis of the results allows to uncouple catalyst deactivation and catalytic reaction and to obtain the kinetic parameters of both processes (i.e., steady-state and deactivation rates, and their apparent activation energies). Deactivation rate of CO formation is one order of magnitude faster than of ethene formation but both processes show the same apparent activation energy, ca. 47 kcal/mol. The apparent activation energy values for the catalytic reaction are 32 ± 4 and 26 ± 2 kcal/mol for the rates of formation of ethene and CO, respectively.

Relation between functionalization degree and activity of strongly acidic polymer supported catalysts

Partial sulfonation of gel-type styrene-co-divinylbenzene polymer is reported and the homogeneity of the sulfonation investigated by electron microprobe analysis of the sulfur content. The morphology of the polymers was characterized by inverse steric exclusion chromatography (ISEC) and the catalytic activity was determined by measuring the reaction rates of three model reactions (synthesis of bisphenol A, alkylation of phenol by 1-octene and reesterification of ethyl acetate with propanol) in a glass CSTR microreactor at steady-state conditions. Distribution of the sulfonic groups within partially functionalized beads looks fairly homogeneous at the electron microprobe resolution scale, but both ISEC morphology characterization and the catalytic experiments indicate the presence of separate sulfonated and unsulfonated domains. The effect of this morphology on the kinetics of catalytic reactions depends on the size of the reacting molecules and their affinity to both the functionalized and unfunctionalized domains of the polymer support. These findings may be useful for the development of other polymer supported catalysts.

On Surface Heterogeneity and Catalytic Kinetics

The effect of surface heterogeneity on catalysis and chemisorption is discussed. Available recent data on calorimetry, as well as on adsorption isotherms and reaction kinetics, are carefully reviewed. Despite the fact that the current catalytic engineering practice is very much limited to Langmuir−Hinshelwood kinetics based on concepts of ideal surfaces, there is a number of cases when such an approach is not sufficient enough for the modeling of the kinetics of heterogeneous catalytic reactions.

Analysis of Simple Kinetic Models in Heterogeneous Catalysis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Periodic Perturbation of the Kinetics of Heterogeneous Catalytic Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Model Studies in Heterogeneous Catalysis. From Structure to Kinetics

Heterogeneous catalysis is one of the fields of modern technology, where the application of complex inorganic materials is of enormous economical importance. For a long time, the chemical and structural complexity of catalyst materials has precluded detailed insights into chemical processes on catalyst surfaces. In the last decades, however, substantial progress has been made toward a microscopic-level understanding of reaction mechanisms and kinetics, mainly based on the development of new well-defined model systems and on advances in experimental technology and theory. Scrutinizing the example of supported model catalysts, we review some of these innovations in model catalysis. As a particular challenging aspect of today’s work, we discuss the question how detailed structural information on the model systems can be linked to catalytic reaction kinetics at the microscopic level.

The influence of atomic order on H 2-induced environmental embrittlement of Ni 3Fe intermetallics

Abstract The different sensitivity to H2-induced environmental embrittlement for the ordered and disordered Ni3Fe alloys has been investigated. The results show no environmental embrittlement in disordered Ni3Fe in gaseous H2 when tested at room temperature. However, the H2-induced environmental embrittlement for the ordered Ni3Fe becomes severer as the degree of order increases. The results of testing on simultaneous hydrogen charging show that disordered Ni3Fe embritted as hydrogen atoms are forced into the material, implying that the embrittlement of ordered Ni3Fe in gaseous H2 is due to the acceleration of the kinetics of catalytic reaction to produce more atomic hydrogen. Further more, the hydrogen adsorption test of Ni3Fe powder shows that the amount of chemically adsorbed hydrogen in the ordered state at room temperature is significantly larger than that adsorbed by the disordered materials, indicating that the more sensitive to H2-induced embrittlement in the ordered Ni3Fe is essentially due to accelerated catalytic reaction to produce more atomic hydrogen.

Diffusional kinetics in the catalytic hydrodechlorination of chlorobenzene in multiphase aqueous mixtures

Abstract The catalytic hydrodechlorination of aqueous mixtures of monochlorobenzene has been investigated experimentally and theoretically. The reaction runs were conducted in a stirred autoclave at T =30 °C, in the presence of pure hydrogen at pressures (kept constant during each reaction run) in the range 2≤ p H 2 ≤60 bar, and using a Pd/C catalyst. Chlorobenzene was loaded in excess with respect to its solubility in water. Therefore, the reacting process involves four phases: (i) gaseous hydrogen; (ii) aqueous solution of monochlorobenzene and hydrogen; (iii) oily droplets of undissolved chlorobenzene; (iv) catalyst solid particles. The theoretical analysis for modelling the overall reactive process has been based on the general results and methods of transport phenomena and of kinetics of heterogeneous catalytic reactions. The experimental data, interpreted in the light of the theoretical model, permit to gain an insight into the Langmuir–Hinshelwood mechanism of the reaction: hydrogen is adsorbed according to a Langmuir-type dissociative adsorption and the rate determining step is the surface reaction. According to this mechanism the reaction rate has a fractional order with respect to hydrogen.

Deactivation kinetics of Ag/Al 2O 3 catalyst for ethylene epoxidation

Abstract Deactivation kinetics of a commercial Ag/Al2O3 catalyst was investigated using accelerated deactivation tests in a Berty-type gradientless recycle reactor. Separability of catalytic reaction and deactivation kinetics were established by operation in a “deactivation compensation” mode, keeping temperature and oxygen concentration constant. It was shown that sintering is the main source for deactivation and that kinetics of deactivation can be described by using a general power-law equation with an order of deactivation equal to 1 with respect to the driving force (a−ass), a being the time-dependent activity and ass the final steady-state activity after an extended period of catalyst operation. The long-time prediction of catalyst behavior suggested that an improved catalyst should work at a lower temperature to avoid sintering.

Design of new catalysts for ecological high-quality transportation fuels by combinatorial computational chemistry and tight-binding quantum chemical molecular dynamics approaches

Abstract Recently, we introduced a concept of combinatorial chemistry to computational chemistry and proposed a new method called “combinatorial computational chemistry”, which enables us to perform a theoretical high-throughput screening of catalysts. In the present paper, we reviewed our recent application of our combinatorial computational chemistry approach to the design of new catalysts for high-quality transportation fuels. By using our combinatorial computational chemistry techniques, we succeeded to predict new catalysts for methanol synthesis and Fischer–Tropsch synthesis. Moreover, we have succeeded in the development of chemical reaction dynamics simulator based on our original tight-binding quantum chemical molecular dynamics method. This program realizes more than 5000 times acceleration compared to the regular first-principles molecular dynamics method. Electronic- and atomic-level information on the catalytic reaction dynamics at reaction temperatures significantly contributes the catalyst design and development. Hence, we also summarized our recent applications of the above quantum chemical molecular dynamics method to the clarification of the methanol synthesis dynamics in this review.

Kinetics of Catalytic Reactions.

Kinetics of Catalytic Reactions.

Kinetics of Heterogeneous Catalytic Reactions.

Kinetics of Heterogeneous Catalytic Reactions.

Transient n-butane partial oxidation kinetics over VPO

Abstract A novel reactor configuration is proposed to study the kinetics of heterogeneous catalytic reactions. It is based on the bubbling fluidization regime; gas velocities are sufficiently low to minimize bypassing but high enough to ensure solids backmixing and a uniform temperature gradient. The reactor is equipped with a gas manifold designed to operate the reactor either under steady-state feed conditions or with cyclical feeds. By cycling VPO catalyst between a reducing environment with butane and an oxidizing environment, we quantify the lattice oxygen contribution to the reaction. Furthermore, we show that carbon can build up on the VPO surface and this phenomenon increases with an increase in the severity of the reducing environment. We propose a simple kinetic model involving three sites—V 5+ , V 4+ and V C4 . The model adequately characterizes the transient partial oxidation of butane but further research is required to create a generalized model that fits all reaction environments.

Modeling of the molecular structure and catalytic activity of the new fullerene‐based catalyst (η2‐c60)pd(PPh3)2: An application in the reaction of selective hydrogenation of acetylenic alcohols

AbstractIn this article we finalize our experimental and theoretical studies on the (η2‐C60)Pd(PPh3)2 palladium–phosphine fullerene complex. Full scale ab initio quantum‐chemical calculations up to the B3LYP/SDDALL level of theory have been performed to determine the structure and electronic spectrum of (η2‐C60)Pd(PPh3)2. Based on the results of calculations and experimental data we conclude that the preliminary interaction of the catalyst with the substrate facilitates the interaction of the substrate–catalyst complex with H2 by decreasing the energy barrier. In conclusions we summarize the results of our studies of the structure and electronic spectrum of the investigated complex, the kinetics of catalytic reactions, the influence of the solvents on the catalyst's activity in the heterogeneous phase, and provide the possible mechanism of catalytic reaction. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Direct Observation of Methyl Radicals Islanding on Copper Surface and Its Effects on the Kinetics of Catalytic Reactions

The formation of methyl radicals into densely packed two-dimensional islands on the Cu(111) surface is directly observed for the first time by scanning tunneling microscopy (STM). It is shown that chemisorbed CH3(ads) molecules tend to aggregate into ( × ) R30° structure in 2D islands at any coverage up to one saturation monolayer. The island sizes depend on the amount of gaseous exposure, and at a given exposure, the sizes are found to decrease when the surface temperature is raised to near the reaction temperature of CH3(ads). The adsorbate islanding behavior can be correlated with the first-order reaction kinetics in the generation of long-chain alkene products detected in the thermal desorption. From this and other related studies on methyl−solid interactions, we infer that the islanding phenomenon may be quite general in catalytic systems.

Classical Kinetics of Catalytic Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oscillatory thermomechanical instability of an ultrathin catalyst.

Because of the small thermal capacity of ultrathin ( approximately 200 nanometers) metal single crystals, it is possible to explore the coupling of catalytic and thermal action at low pressures. We analyzed a chemothermomechanical instability in this regime, in which catalytic reaction kinetics interact with heat transfer and mechanical buckling to create oscillations. These interacting components are separated and explored through experimentation, mathematical modeling, and scientific computation, and an explanation of the phenomenon emerges from their synthesis.

Neural networks for modelling of kinetic reaction data applicable to catalyst scale up and process control and optimisation in the frame of combinatorial catalysis

Abstract This work describes an application of artificial neural networks (ANNs) for modelling the kinetics of catalytic reactions using methods not based on fundamental knowledge. Thus, neural networks have been used to model the behaviour of different reactions under different reactor conditions. The modelling of catalytic reactions by neural networks has been demonstrated, and the influence of experimental error in input data has been estimated. In addition, a novel methodology for modelling catalytic data employing already-trained neural networks has been systematically studied by using experimental results from the catalytic hydroisomerization of different n -paraffins. It can be then expected that a new reaction system can be rapidly analysed with a small number of experiments if a library of well-trained neural networks which represent a series of different reaction networks is constructed.