Single site reaction mechanism

Selective oxidation of CO in hydrogen over different catalysts has been extensively examined. Most research to date has occurred with formulations that include a precious metal component supported on an alumina carrier. The catalyst-mediated oxidation of CO is a multistage process, commonly obeying Langmuir-Hinshelwood kinetics for a single-site competitive mechanism between CO and 02. Initially, CO is chemisorbed on a PGM surface site, while an 02 molecule undergoes dissociative chemisorption either on an adjacent site or on the support in order for surface reaction between chemisorbed CO and O atoms to produce C02. 

Riser technology appears to be quite versatile. Patience and Mills [33] investigated propylene oxidation into acrolein and found that this technique has a potential for the commercial scale production of acrolein. Their kinetic model was based on a simplified single site redox mechanism involving consecutive-parallel reactions for the partial and complete oxidation of propylene. Its predictions of the performance of the reactor gave correct trends. 

Equation 3, however, requires that monomer coordination is the rate-determining step. However, there are many observations which are very difficult to explain by a simple single-site Cossee mechanism, such as a reaction rate order higher than one reported for propene,ethene, styrene,and diene ° ° polymerizations. 

In the context of this study, the extent of reaction refers to the conversion of sites from active to inactive, and is given by Equation 6 (i.e., x = 1 for no conversion, x = 0 for total conversion). For a single site mechanism it can be shown easily that F(x) reduces to 1.0. Solution of Equation 7 and substitution into Equation 3 yields the expected result ... 

Hint. For the single-site mechanism assume (as Mathur and Thodos did) that the surface reaction step can be written as ... 

Tropf, S. et al., Reaction mechanisms of homodimeric plant polyketide synthases (stilbenes and chalcone synthase) a single active site for the condensing reaction is sufficient for synthesis of stilbenes, chalcones, and 6 -deoxychalcones. J. Biol. Chem., 270, 7922, 1995. 

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