Heterogeneons Systems

We have seen that the relative photonic efficiency ( rei) introdnced earlier (Serpone et at, 1996) can compare photochemical activities of different heterogeneons systems. It can also be represented as the ratio between the photonic efficiency of a given reaction ( ) to the photonic efficiency st of a standard reaction (the photodegradation of phenol and TiOi Degnssa (now Evonik) P-25 were chosen for simplicity to describe the standard process and photocatalyst, respectively) see eq. 5.93. 

When carbon monoliths are to be nsed in a heterogeneons system, there are some important considerations to make. If the kinetics of the reaction are not... 

Since the rates of formation or disappearance are intensive properties, it is convenient to relate them to a reference system. In a homogeneous phase system, the unit of volume (mol/Lh) is used as reference. On the other hand, in heterogeneons systems, we used as reference the superficial or interfacial area (mol/m h). 

In biological systems, the enzymes are homogeneons catalysts. For their use in heterogeneons electrochemical reactions, they mnst be immobilized on a carrier suitable for fashioning an electrode. This is most often achieved by adsorption of the enzyme on a carbon material (carbon black, graphite, etc.). This immobilization usually leads to some decrease in activity of the enzymes, bnt on the other hand, raises their stability. 

Emeline A. V., Polikhova S., Andreev N., Ryabchnk V. K. and Serpone N. (2002b), Photoinduced processes in heterogeneons gas-solid systems. Temperature dependence (100-600 K) and modelling of a snrface chemical reaction on zirconia that triggers photophysical events in the solid , J. Phys. Chem. B 106, 5956-5966. 

At present it is known [1] that the majority of catalytic systems are nanosystems. At the heterogeneons catalysis active substance one tries to deposit on the bearers in a nanoparticles form in order to increase their specific surface. At homogeneous catalysis active substance molecules by themselves have often nanometer sizes. It is known too [2] that the operating properties of heterogeneous catalyst systems depend on their geometry and structure of the surface, which can influence strongly on catalytic properties, particularly, on catalysis selectivity. It has been shown experimentally [3] that the montmoril-lonite surface is a fractal object. Proceeding from this, the authors [4] studied the montmorillonite fractal surface effect on its catalytic properties in isomerization reaction. 

A high scale-up factor in Table 2.1 reflects the ease in scahng up of the reactor. It can be seen that heterogeneons/mnltiphase reactors have substantially smaller scale-up factors than those for homogeneous systems. This is due to the complex nature of scale-dependent diffnsional processes (Section 2.4). 

Cavallo, L. Gnerra, G Corradini, P. Mechanisms of propagation and termination reactions in classical heterogeneons Ziegler-Natta catalytic systems A nonlocal density functional study. J. Am. Chem. Soc. 1998,120, 2428-2436. 

Recent studies have explored health-based adaptations at all levels (subsystem, system, and systems-of-systems layers) of a heterogeneons, multi-vehicle system. This emphasis on health awareness has the potential to address two needs (1) to improve safety, overall system performance, and reliability and (2) to meeting the expectations (situational awareness, override capability, and task or mission deflnition) of human operators, who are inevitably present. 

Heterogeneons polymerization system is a two-phase system where the starting monomer and the resulting polymer are in the form of a fine dispersion in an immiscible liquid medium. The processes can be classified as emulsion, microemulsion and miniemulsion techniques depending on the initial state of polymerization mixtnre, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles. The nanoparticles sizes are sensitive to several parameters used during the synthesis process, such as amphiphilicity and molecular weight of encapsulation matrices, initial concentration of functional polymer and the miscibility of the functional polymer in aqueous media [44]. 

---