Reaction in heterogeneous

CHEMILUMINESCENCE REACTIONS IN HETEROGENEOUS SYSTEMS FOR TRACE DETERMINATION OF BIOLOGICALLY... 

Present research is devoted to investigation of application of luminol reactions in heterogeneous systems. Systems of rapid consecutive reactions usable for the determination of biologically active, toxic anions have been studied. Anions were quantitatively converted into chemiluminescing solid or gaseous products detectable on solid / liquid or gas / liquid interface. Methodology developed made it possible to combine concentration of microcomponents with chemiluminescence detection and to achieve high sensitivity of determination. 

Hinshelwood Kinetic mechanism of reactions in heterogeneous catalysis... 

In particular, reactions in heterogeneous catalysis are always a series of steps, including adsorption on the surface, reaction, and desorption back into the gas phase. In the course of this chapter we will see how the rate equations of overall reactions can be constructed from those of the elementary steps. 

Figure 2.7. Schematic representation ofthe simplest possible reaction in heterogeneous catalysis.

The similarities of above experimental results inspired us to investigate the role of SE in heterogeneous catalytic enantioselective hydrogenation reactions. In heterogeneous catalytic reaction the SE means that a given template molecule interacts with the prochiral substrate in the liquid phase in such a way that one of the prochiral sites is preferentially shielded. If the substrate is shielded then its adsorption onto the metal can take place with its unshielded site resulting in ED. 

E. Polastro, in G. Jannes, V. Dubois (Eds.), Chiral Reactions in Heterogeneous Catalysis. Plenum Press, New York, 1995, p. 5. 

Shock-induced Chemical Reactions in Heterogeneous Multi-Material Powder Mixtures. 

Other Fe-S Clusters. Spontaneous self-assembly reactions using phosphines as terminal ligands have been reported to yield a variety of new Co-S (22) and Ni-S clusters (23). Extension to Fe-S clusters was initially effected by the following reaction in heterogeneous solution (2A). 

Rasch Angew. Chem. Int. Ed. Engl. 1994, 33, 2144. (c) H.-U. Blaser, B. Pugin In Chiral Reactions in Heterogeneous Catalysis,... 

The first example cited is one in which the solid is totally consumed, whereas the second and third examples involve the formation of a new solid product which might be either a desired product, as in the second case, or a waste product (the gangue) as in the third example. Despite such fundamental differences from catalytic reactions, there are many similarities. In each case, chemisorption, surface chemical reaction emd diffusion through porous media occurs which is in common with heterogeneous chemical reactions. Hence, models representing the dynamics of these non-catalytic gas—solid processess incoporate the same principles of chemical reaction concomitant with diffusion and reaction in heterogeneous catalysts. 

Some of the basic concepts and technologies are described here. Catalysis can be divided into two types (1) homogeneous and (2) heterogeneous reactions. In homogeneous reactions, the reaction occurs between similar species, e.g. liquid-liquid reactions. In heterogeneous reactions, the reaction occurs between different types of species, e.g. gas-solid, liquid-solid and liquid-gas. Many industrial reactions are heterogeneous gas-solid or liquid-solid reactions. We will concentrate first on gas reactions occurring at solid catalyst surfaces ... 

The net result of a photochemical redox reaction often gives very little information on the quantum yield of the primary electron transfer reaction since this is in many cases compensated by reverse electron transfer between the primary reaction products. This is equally so in homogeneous as well as in heterogeneous reactions. While the reverse process in homogeneous reactions can only by suppressed by consecutive irreversible chemical steps, one has a chance of preventing the reverse reaction in heterogeneous electron transfer processes by applying suitable electric fields. We shall see that this can best be done with semiconductor or insulator electrodes and that there it is possible to study photochemical primary processes with the help of such electrochemical techniques 5-G>7>. 

The Rate-Determining Step. Determination of the step that decides the overall rate in a series of consecutive or parallel reactions in heterogeneous catalysis is the most significant part of mechanism determination. It is best to deal with the ideas here in a general way they will be exemplified in three reactions later on in the section. 

McClements, D.J., Decker, E.A. (2000). Lipid oxidation in oil-in-water emulsions impact of molecular environment on chemical reactions in heterogeneous food systems. Journal of Food Science, 65, 1270-1282. 

In general, bioreactions can occur in either a homogeneous hquid phase or in heterogeneous phases including gas, hquid, and/or sohd. Reactions with particles of catalysts, or of immobilized enzymes and aerobic fermentation with oxygen supply, represent examples of reactions in heterogeneous phases. 

There are many more types of elementary processes in heterogeneous catalysis than in gas phase reactions. In heterogeneous catalysis the elementary processes are broadly classified as either adsorption-desorption or surface reaction, i.e., elementary processes which involve reaction of adsorbed species. Free surface sites and molecules from the fluid phase may or may not participate in surface reaction steps. 

---