Homogeneous catalysis heterogeneous catalyst

Pioneering works in this area started in the 1960s by polymer scientists like D. Ballard at ICI and Y. Yermakov at the Novosibirsk Institute of Catalysis [54,55]. The need for polymers with better properties and for better technologies (gas phase processes) has led to the development of various strategies to obtain supported catalytic systems [56-58]. Here, we will concentrate on reactions leading to basic chemicals, and a comparison between homogeneous and heterogeneous catalysts will be performed when possible. 

In homogeneous catalysis soluble catalysts are applied, usually in the liquid phase, in contrast to heterogeneous catalysis, where solid catalysts are used. Homogeneous catalysis is applied in many processes in both bulk and fine chemicals production. 

Catalysis is known as the science of accelerating chemical transformations. In general, various starting materials are converted to more complex molecules with versatile applications. Traditionally, catalysts are divided into homogeneous and heterogeneous catalysts, biocatalysts (enzymes), photocatalysts, and electrocatalysts, which are mainly used... 

Biocatalysis is a rather special case, somewhere between homogeneous and heterogeneous catalysis. In most cases, the biocatalyst is an enzyme - a complex protein that catalyzes the reactions in living cells. Enzymes are extremely effident catalysts. An enzyme typically completes 1000 catalytic cycles in one second. Compared to this, conventional homogeneous and heterogeneous catalysts are slow and inefficient (100-10000 cydes per hour). Speed, however, is not the only advantage enzymes specialize in converting one specific reactant into another... 

Complex formation in homogeneous catalysis and adsorption on a catalyst surface share the same principle the total number of sites is constant. The rate expressions for homogeneous and heterogeneous catalysts therefore have a similar form. Usually, for gas phase reactions, partial pressures are used, whereas concentrations are employed for liquid phase reactions. This only has consequences for the dimensions of the constants in the rate expressions. The following approach to the derivation of these rate expressions can be applied to homogeneous as well as to heterogeneous catalyst systems. 

Catalysed substitution reactions of an unusual kind are collected together in this section. In each case, the catalysis of the reaction by a homogeneous entity is assisted by the surface of a solid. The resulting reinforcement of catalytic effects is frequently described as synergistic. The homogeneous and heterogeneous catalysts quite often possess a species in common, for example Ag+ ions and solid Agl, and many of the homogeneously catalysed reactions exhibit autocatalysis as a result. 

The aromatization reaction in this case is an example of homogeneous catalysis. The catalyst, reactant, and product are all dissolved in liquid styrene monomer. As such, traditional heterogenous catalysis considerations such as... 

Catalysis are classified into two types homogeneous and heterogeneous. In homogeneous catalysis the catalyst is present in the same phase as the reactants, as when a gas-phase catalyst speeds up a gas-phase reaction, or a species dissolved in solution speeds up a reaction in solution. Chlorofluorocarbons and oxides of nitrogen are homogeneous catalysts responsible for the destruction of ozone in the stratosphere. These reactions are examined in more detail in Section 20.5. A second example is the catalysis of the oxidation-reduction reaction... 

Such species are also part of the evolution of homogeneous and heterogeneous catalysts, including key oxidation and olefin polymerization processes. A burgeoning area is controlled immobilization of reactive centers on solid surfaces. In recognition, this Chapter concludes with a commentary on the development of heterogeneous catalysis and the synthesis of surfaces with controlled properties. 

The term reactive distillation (RD) refers to both catalyzed and uncatalyzed reaction systems. Catalytic distillation systems may use a homogenous or heterogenous catalyst to accelerate the reaction. Reactive distillation is a well-known example of reactive separation process, and is used commercially. The first patent and early journal articles deal mainly with homogenously catalyzed reactions such as esterifications, transesterifications, and hydrolysis.f Heterogenous catalysis with RD is a more recent development. The key advantages for a properly designed RD colunm are complete conversion of reactants and attainment of high selectivity. An example of the benefits of RD is the acid catalyzed production of methyl acetate by... 

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