Spatially controlled reaction environment

In the last three decades, we have designed and successfully prepared various supported metal complexes on oxide surfaces that exhibit unique catalytic activities and selectivities that are different from those of their homogeneous analogues [3,4,9, 12-15]. With the aid of several sophisticated spectroscopic techniques, the structures and roles of catalytically active species on surfaces have been characterized and identified [3, 4,9,12-25]. Chemical interactions between metal complexes and oxide surfaces can provide new reactivity of metal species by the construction of a spatially controlled reaction environment and the formation of unsaturated active metal species, leading to high catalytic activity, selectivity and durability [21-25]. 

Therefore, the simplest procedure to get the stochastic description of the reaction leads to the rather complicated set of equations containing phenomenological parameters / (equation (2.2.17)) with non-transparent physical meaning. Fluctuations are still considered as a result of the external perturbation. An advantage of this approach is a useful analogy of reaction kinetics and the physics of equilibrium critical phenomena. As is well known, because of their nonlinearity, equations (2.1.40) reveal non-equilibrium bifurcations [78, 113]. A description of diffusion-controlled reactions in terms of continuous Markov process - equation (2.2.15) - makes our problem very similar to the static and dynamic theory of critical phenomena [63, 87]. When approaching the bifurcation points, the systems with reactions become very sensitive to the environment fluctuations, which can even produce new nonequilibrium transitions [18, 67, 68, 90, 108]. The language developed in the physics of critical phenomena can be directly applied to the processes in spatially extended systems. 

In the catalytic system shown in Scheme 9, a hydrogen bond between one hydroxy function of the diol catalyst and the carbonyl group of the substrate is regarded as the driving force of catalysis. Here, the spatial orientation of the bulky a-1-naphthyl substituents of the TADDOL (a,a,a, a -tetraaryl-l,3-dioxolan-4,5-dimethanol) scaffold generates the chiral environment controlling the enantioselectivity of the reaction. 

A key aspect of metal oxides is that they possess multiple functional properties acid-base, electron transfer and transport, chemisorption by a and 7i-bonding of hydrocarbons, O-insertion and H-abstraction, etc. This multi-functionality allows them to catalyze complex selective multistep transformations of hydrocarbons, as well as other catalytic reactions (NO,c conversion, for example). The control of the catalyst multi-functionality requires the ability to control not only the nanostructure, e.g. the nano-scale environment around the active site, " but also the nano-architecture, e.g. the 3D spatial organization of nano-entities. The active site is not the only relevant aspect for catalysis. The local area around the active site orients or assists the coordination of the reactants, and may induce sterical constrains on the transition state, and influences short-range transport (nano-scale level). Therefore, it plays a critical role in determining the reactivity and selectivity in multiple pathways of transformation. In addition, there are indications pointing out that the dynamics of adsorbed species, e.g. their mobility during the catalytic processes which is also an important factor determining the catalytic performances in complex surface reaction, " is influenced by the nanoarchitecture. 

The past decade has seen a dramatic improvement in the strategies and instrumentation available to characterize the structures of interfacial supramolecular assemblies. Current thrusts are towards in situ techniques that probe the structure of the interfacial supramolecular assembly with increasingly fine spatial and time resolution. The objective of this field is to assemble reaction centers around which the environment is purposefully structured at the molecular level, but extends over supramolecular domains. The properties of the assembly are controlled not only by the properties of the molecular building blocks but especially by the interface. Therefore, the focus is on both the interfacial and bulk properties of monolayers and thin films. Issues that need to be addressed include the film thickness, structural homogeneity and long-range order, as well as the electrochemical and... 

We have developed several new measurement techniques ideally suited to such conditions. The first of these techniques is a High Pressure Sampling Mass Spectrometric method for the spatial and temporal analysis of flames containing inorganic additives (6, 7). The second method, known as Transpiration Mass Spectrometry (TMS) (8), allows for the analysis of bulk heterogeneous systems over a wide range of temperature, pressure and controlled gas composition. In addition, the now classical technique of Knudsen Effusion Mass Spectrometry (KMS) has been modified to allow external control of ambient gases in the reaction cell (9). Supplementary to these methods are the application, in our laboratory, of classical and novel optical spectroscopic methods for in situ measurement of temperature, flow and certain simple species concentration profiles (7). In combination, these measurement tools allow for a detailed fundamental examination of the vaporization and transport mechanisms of coal mineral components in a coal conversion or combustion environment. 

The cages and channels within microporous solids provide unique, crystallo-graphically well-defined, nanometre-scale environments in which chemical reactions may be performed. Molecules can be introduced into sites where they are separated from other molecules. Ingenious ship-in-a-bottle type syntheses of complexes and the study of photochemical reactions on isolated molecules are examples of this kind where the spatial separation of molecules is important in the chemical behaviour. The ability of zeolites to control the position and orientation of included molecules can introduce potentially interesting optical or electronic properties to the resultant organic-inorganic arrays. 

From the electric point of view, designing cathodic protection installations is based on the determination of the spatial distribution of the electric field intensity between anodes and the protected structure as the cathode. Classic cathodic protection systems operate in ohmic control conditions (Morgan, 1987 Benedict, 1986). This means that the resistance magnitude between anodes and the protected structure is a factor affecting the distribution of electric field force lines. The transfer resistance between the anode and the electrolytic environment connected with electrochemical reactions, and the transfer resistance between the electrolytic environment and the cathode, are usually insignificantly small in relation to the... 

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