Homogeneous chemical reactions difference between heterogeneous

In the sections that follow, we will learn about both homogeneous and heterogeneous chemical reactions. It is important to understand the difference between them. 

Obviously, the heterogeneous character of electrochemical process can in some cases lead to essential differences between electrode and homogeneous reaction pathways. Therefore, eventually it needs to verify the results by studying of reactions in homogeneous media. In other words, the problem of correcmess of electrochemical modeling should be analyzed for each reaction anew and at the same time be checked chemically, that is, in the pure liquid-phase conditions. 

There are indeed significant fundamental and practical differences between classical organic reactions (either stoichiometric or homogeneously catalysed ones) and those catalysed by solids and especially zeolites (Table 2.1). It is also the case when one compares the relatively simple transformations generally studied by the specialists in Heterogeneous Catalysis and the transformation of complex molecules involved in the synthesis of Fine Chemicals. The operating conditions are very different high temperature, gas phase, fixed bed reactors on the one hand low... 

Transport problems in discontinuous (heterogeneous) system discuss the flows of the substance, heat, and electrical energy between two parts of the same system. These parts or phases are uniform and homogeneous. The two parts make up a closed system, although each individual part is an open system, and a substance can be transported from one part to another. There is no chemical reaction taking place in any part. Each part may contain n number of substances. For example, thermal diffusion in a discontinuous system is usually called thermal osmosis. If the parts are in different states of matter, there will be a natural interface. However, if both parts are in liquid or gas phases, then the parts are separated by a porous wall or a semi-permeable membrane. 

Solid-catalyzed reactions are generally examined in continuous-flow reactors, while homogeneously catalyzed reactions (including reactions catalyzed by non-immobilized biocatalysts) are usually studied in batch reactors. An important difference between chemical catalysis and biocatalysis is that it is relatively easy to study the biocatalyst either as a homogeneous or a heterogeneous catalyst, as desired. 

Two ways in which catalytic oxidation for control of trace VOCs can be carried out are shown in Figure 1. The first uses a direct contact open flame to preheat" the gas stream upstream of the catalyst. In this configuration, the open flame both preheats the gas stream to an elevated temperature so catalytic oxidation can take place and actually accomplishes some measure of VOC oxidation. This preheat" flame may accomplish a significant portion of the overall observed oxidation. The chemical mechanism of open flame oxidation involves free radical-induced homogeneous reactions and is fundamentally different from heterogeneous catalytic oxidation, which involves activated complexes formed on the catalyst surface. The second method involves only a catalyst bed, over which the gas stream passes, usually after some indirect preheating. The difference between these two configurations is the presence of an open flame, but this difference can be important because the mechanism of oxidation on a catalyst in close proximity to a flame may be different from that on a catalyst by itself. 

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