Interpretation of Heterogeneous Kinetic Rate Data Via Hougen-Watson Models

14-8 INTERPRETATION OF HETEROGENEOUS KINETIC RATE DATA VIA HOUGEN-WATSON MODELS 

As a practical example of the interpretation of kinetic rate data to distinguish between more than one reaction mechanism, consider the dehydrogenation of ethanol (i.e., CH3CH2OH, [A]) to acetaldehyde (i.e., CH3CHO, [C]) and hydrogen (i.e., H2, [D]). The reversible chemical reaction that occurs on a catalytic 

If each component experiences single-site adsorption and dual-site chemical reaction is the slowest step, then the following four-step mechanism is reasonable  

The Hougen-Watson model that is consistent with this mechanism is proportional to the square of the vacant-site fraction because two active sites are required in the rate-limiting step. Hence, 

If hydrogen volatilizes immediately upon dehydrogenation of ethanol, and H2 does not occupy an active site on the catalytic surface, then the following three-step mechanism is more appropriate  

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