Nanomaterials kinetic studies

The book focuses on three main themes catalyst preparation and activation, reaction mechanism, and process-related topics. A panel of expert contributors discusses synthesis of catalysts, carbon nanomaterials, nitric oxide calcinations, the influence of carbon, catalytic performance issues, chelating agents, and Cu and alkali promoters. They also explore Co/silica catalysts, thermodynamic control, the Two Alpha model, co-feeding experiments, internal diffusion limitations. Fe-LTFT selectivity, and the effect of co-fed water. Lastly, the book examines cross-flow filtration, kinetic studies, reduction of CO emissions, syncrude, and low-temperature water-gas shift. 

In studies of reactions in nanomaterials, biochemical reactions within the cell, and other systems with small length scales, it is necessary to deal with reactive dynamics on a mesoscale level that incorporates the effects of molecular fluctuations. In such systems mean field kinetic approaches may lose their validity. In this section we show how hybrid MPC-MD schemes can be generalized to treat chemical reactions. 

Not mentioned in this review but certainly important to multiscale modeling related to solid mechanics are topics, such as self-assemblies, thin films, thermal barrier coatings, patterning, phase transformations, nanomaterials design, and semiconductors, all of which have an economic motivation for study. Studies related to these types of materials and structures require multiphysics formulations to understand the appropriate thermodynamics, kinetics, and kinematics. 

The stmctural diversity of carbon at the nanoscale exceeds that of all other materials [1]. Detailed information on the nature of the material and the structure-dependency of the oxidation kinetics is thus crucial for providing the required selectivity. While some nanomaterials, such as carbon nanotubes, have been studied extensively and are generally well understood, other nanostructures such as nanodiamond (ND) have received much less attention. However, in order to study their properties and open avenues for new applications, one has to provide a material of high purity and defined composition. 

In order to successfully apply oxidation methods to carbon nanomaterials, one has to systematically study their interactions with gases and liquids, monitor changes in structure and composition, and simultaneously follow the reaction kinetics of the different carbon nanostructures. This has been partially achieved for carbon nanotubes [25-27], which have been thoroughly studied, but remains a major challenge for other forms of carbon, including ND or carbon onions. 

Much of the work to date on particle size effects on phase transformation kinetics has involved materials of technological interest (e.g., CdS and related materials, see Jacobs and Alivisatos, this volume) or other model compounds with characteristics that make them amenable to experimental studies. Jacobs and Alivisatos (this volume) tackle the question of pressure driven phase transformations where crystal size is largely invariant. In some ways, analysis of the kinetics of temperature-motivated phase transformations in nanoscale materials is more complex because crystal growth occurs simultaneously with polymorphic reactions. However, temperature is an important geological reality and is also a relevant parameter in design of materials for higher temperature applications. Thus, we consider the complicated problem of temperature-driven reaction kinetics in nanomaterials. 

Others authors propose alternative ways to conduct or discuss an experiment that is already commonly used in the teaching of chemical kinetics. For example the presentation of a videotaped clock (iodine-azide) reaction which is suitable for videotaping and which has an easily determined mechanism (Haight Jones, 1987) the determination of a reaction mechanism of the blue bottle reaction (Engerer Cook, 1999). Others may be used to discuss thermodynamics and kinetics simultaneously, e.g., from the study of the surface of nanomaterials (such as a gold colloid monolayer) (Keating, Musick, Keefe Natan, 1999), and from the study of a chemical equihbrium in solution (Leenson, 1986). 

There are a number of methods for the S5mthesis of different upon nature nanoparticles and nanomaterials, however the kinetic peculiarities and regularities of the formation (nucleation and propagation) of nanoparticles studied insufficiently. 

Cervera et al. [222] studied the controlled release of phenytoin, which is an anticonvulsant drug for the treatment of epilepsy, from nanostructured Ti02 reservoirs. The y loaded the Ti02 reservoirs with 5 wt% phenytoin, and studied the release kinetics in a pH 7.2 buffer by measuring the ultraviolet-visible (UV-vis) absorbance spectrum as a function of time. The authors also explored the relationship between the phenytoin release rate and the properties of the Ti02 nanomaterials used in the preparation of the reservoir. The results showed that the reservoirs are capable of releasing phenytoin for more than 45 days, and that the release kinetics are characterized by two regimes an initial fast release and a subsequent slow release. The slow release rate is independent of time and showed... 

Although oxidation has been used widely to purify carbon materials, carbon-oxygen reactions have also been shown to drastically alter the physiochemical properties of nanostructures, particularly their wettability and adsorption/desorption characteristics. Moreover, oxidation potentially induces damage to carbon nanomaterials or even destroys the structures under improper conditions. To fully utilize the selectivity of the oxidation process at the nanoscale, a comprehensive understanding of the chemical and physical nature of a material and the structure dependence of the oxidation kinetics is required. For the latter, one must systematically study the interactions of the different carbon nanostructures with gaseous and liquid oxidizer, monitor changes in structure and composition, and analyze the reaction kinetics in greater detail. 

Co-precipitation methodology is the most cotmnon synthesis techniqne to obtain LDHs, however nucleation and the kinetics growth can not be controlled easily. An alternative method for the synthesis of nanomaterials is reverse microemnlsion (water-in-oil) in which an aqueous phase is dispersed into an oil phase stabihzed by a surfactant film. Microemulsions can be used as nanoreactors leading to homogeneous nanomaterials with a narrow particle size and better textural properties [3]. In this work, Mn and binary Mn-Cu, Mn-Co hydrotalcite-like precursors synthesized in reverse microemulsion and the effects of preparation methods on the performance of catalysts for deep oxidation of VOCs have been studied. 

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