Homogeneous catalysis complex rate models

EXTENSION TO COMPLEX RATE MODELS HOMOGENEOUS CATALYSIS... 

Recall that there are a number of reactions where homogeneous catalysis involves two phases, liquid and gas, for example, hydrogenation, oxidation, carbonylation, and hydroformylation. The role of diffusion becomes important in such cases. In Chapter 6, we considered the role of diffusion in solid catalyzed fluid-phase reactions and gas-liquid reactions. The treatment of gas-liquid reactions makes use of an enhancement factor to express the enhancement in the rate of absorption due to reaction. A catalyst may or may not be present. If there is no catalyst, we have a simple noncatalytic gas-liquid heterogeneous reaction in which the reaction rate is expressed by simple power law kinetics. On the other hand, when a dissolved catalyst is present, as in the case of homogeneous catalysis, the rate equations acquire a hyperbolic form (similar to LHHW models discussed in Chapters 5 and 6). Therefore, the mathematical analysis of such reactions becomes more complex. 

The Michaelis-Menten equatioa 10.2-9, is developed in Section 10.2.1 from the point of view of homogeneous catalysis and the formation of an intermediate complex. Use the Langmuir-Hinshelwood model of surface catalysis (Chapter 8), applied to the substrate in liquid solution and the enzyme as a colloidal particle with active sites, to obtain the same form of rate law. 

The nickel-catalyzed cyclooligomerization of butadiene (BD) is one of the most thoroughly studied homogeneous catalytic reactions. Extensive NMR studies of intermediates and model compounds have recently been reported. It provides one of the best examples of the ability of phosphorus ligands to control both rates and product distributions in homogeneous catalysis and shows just how complex catalytic systems can become. 

Non-linear reaction rate expressions that are adequate for reactor design frequently contain more unknown parameters than can be evaluated by either classical kinetics or non-linear statistical methods. Sucl expressions are encountered in both heterogeneous and homogeneous catalysis, and in biochemistry. Fifteen o more non-linear parameters are not uncommon in rate models for complex industrial reactions. 

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