Solid supports, dynamic processes

Adsorption of carotenoids on activated silica-alumina results in their chemical oxidation and carotenoid radical formation. Tumbling of carotenoid molecules adsorbed on solid support is restricted, but the methyl groups can rotate. This rotation is the only type of dynamic processes which is evident in the CW ENDOR spectrum. 

Dynamic Processes of Metal Atoms and Small Metal Clusters in Solid Supports... 

FIGURE 29 Schematic representation of the dynamic processes that determine the formation of the active catalyst phase from vanadyl pyrophosphate. The dashed separation in solid-state and catalytic regimes is artificial and supports only the explanation of the complex interrelations. Reproduced with permission from Ref. (757). Copyright... 

Theoretical studies of the properties of the individual components of nanocat-alytic systems (including metal nanoclusters, finite or extended supporting substrates, and molecular reactants and products), and of their assemblies (that is, a metal cluster anchored to the surface of a solid support material with molecular reactants adsorbed on either the cluster, the support surface, or both), employ an arsenal of diverse theoretical methodologies and techniques for a recent perspective article about computations in materials science and condensed matter studies [254], These theoretical tools include quantum mechanical electronic structure calculations coupled with structural optimizations (that is, determination of equilibrium, ground state nuclear configurations), searches for reaction pathways and microscopic reaction mechanisms, ab initio investigations of the dynamics of adsorption and reactive processes, statistical mechanical techniques (quantum, semiclassical, and classical) for determination of reaction rates, and evaluation of probabilities for reactive encounters between adsorbed reactants using kinetic equation for multiparticle adsorption, surface diffusion, and collisions between mobile adsorbed species, as well as explorations of spatiotemporal distributions of reactants and products. 

Fig. III-29. The molecular dynamic simulation of the behavior of a droplet of liquid placed on a solid support a - spreading, b - gathering of liquid into a droplet in the case of nonwetting, c - fluctuations of a droplet under the condition of non-wetting, d - effect of a surfactant on wetting process [29]...

The term catalyst surface is used broadly here. The dynamic processes of interest may include surface restructuring, diffusion of species into the bulk of solid catalyst pellets, reactions in liquid phase supported in a porous catalyst pellets, etc. 

The liquid-solid interface supports the growth of 2D crystals on surfaces too. The liquid phase acts as a reservoir of dissolved species which can diffuse towards the substrate, adsorb, diffuse laterally and desorb. These dynamic processes favor the repair of defects. Under equihbrium conditions, relatively large domains of well-ordered patterns are formed. Large domains grow at the expense of small domains via a process which is called Ostwald ripening. Furthermore, the solvent plays a significant role in the network formation. The choice of solvent affects the mobility of molecules, especially, the adsorption-desorption dynamics via the solvation energy and possibly also via solvent viscosity. 

The primary function of chromatography is separation of a mixture of compounds into individual components. It is a dynamic separation system that is composed of two media, a stationary phase and a mobile phase. The stationary phase in most applications is a liquid supported on the surface of an inert solid support and is usually packed in a column. The mobile phase can be a gas, a liquid, or a supercritical fluid. Its purpose is to transport the sample through the column, a process known as elution. The components in a separation mixture distribute between these two phases to a different extent. A component that interacts... 

While the precise nature of the mechanism of separation of compounds by ion-pair chromatography has been thoroughly examined and is still the subject of considerable debate (146, 362, 369), the basic features can be summarized by a series of equilibria representing the partitioning and/or adsorption of the ions and the complex between the mobile and stationary phases. The equilibria pertinent to reversed phases (Fig. 2.22) account for the possibility of ion-pair formation in either the mobile or stationary phases as well as the partitioning of the ions and the complex between the two phases. When normal phases are considered, equilibria accounting for appropriate interactions with the normal-phase solid support as well as with the stationary aqueous phase bound to the solid support must also be included. The relative influence of these dynamic processes depends upon the nature of the solute, counter ion, mobile phase, and stationary... 

Energy and natural resources processing. NSF should sustain its support of basic research in complex behavior in multiphase systems, catalysis, separations, dynamics of solids transport and handling, and new scale-up and design methodologies. 

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