Nitrogen oxides homogeneous catalysts

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... 

Nitrogen ligands are the most donor functions in enzymes, the oldest homogeneous catalysts. Here they occur in imidazoles, porphyrins, binding to metals such as copper and iron, and they are involved in many oxidation reactions. Numerous mimics of these complexes are used in homogeneous... 

In the oxidative coupling of primary aromatic diamines to azopolymers cupric ion/nitrogen base complexes serve as homogeneous catalysts. Such complexes are best prepared in situ by oxygenating a cuprous species, preferably CuCl or Cu O/HCl, in the presence of the nitrogen base. Cupric salts investigated except for cupric acetate yielded inactive species. 

Catalytic combustion is an environmentally-driven, materials-limited technology with the potential to lower nitrogen oxide emissions from natural gas fired turbines consistently to levels well below 10 ppm. Catalytic combustion also has the potential to lower flammability at the lean limit and achieve stable combustion under conditions where lean premixed homogeneous combustion is not possible. Materials limitations [1,2] have impeded the development of commercially successful combustion catalysts, because no catalytic materials can tolerate for long the nearly adiabatic temperatures needed for gas turbine engines and most industrial heating applications. 

The superiority of the nitrogen oxide catalysts over the solid catalysts may also in part he due to the homogeneous type of reactions possible in such gas mixtures as have been used. It is quite probable that the formaldehyde is adsorbed more strongly on the solid catalysts than is methane with the result that it is snbjccted to even more severe oxidation conditions than would be the case in the absence of active solid surfaces. 

Chapter 6 provides an extensive review of the uses of carbon as a catalyst, with particnlar emphasis being placed on cases in which active sites have been properly identified and activity correlations established. The special case of nitrogen-doped carbons and their catalytic activity in oxidation reactions is discussed in Chapter 7, and Chapter 8 covers the heterogenization of homogeneous catalysts by anchoring transition-metal complexes onto the snrface of suitable carbon materials. 

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