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https://hdl.handle.net/2142/66643
Description
Title
Dynamics of Carbon-Monoxide Oxidation on Platinum
Author(s)
Zhang, Sean Xianming
Issue Date
1980
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
This work presents a study of kinetics of CO oxidation on a platinum ribbon in a gradientless reactor. An isothermal condition was maintained on the catalyst surface. The reaction rate was measured by a calorimetric technique, and measurements of the effluent CO(,2) concentration were made with an Infrared analyzer. The experimental system proved to be capable of yielding reproducible data and of exploring new phenomena and reaction behavior in general.
Gas impurities were found to be responsible for the oscillatory behavior in the gas temperature range of 150 to 300(DEGREES)C and CO feed concentrations of .8 to 2.0%.
Multiplicity was exhibited in a clean reaction system. Simple hysteresis consisting of two stable steady states existed at 1.9% or lower CO feed concentrations. For a feed of 1.9% or higher CO in air, complex hysteresis was observed where three stable steady states existed in a narrow range of platinum surface temperatures.
The kinetic model describing the reaction system predicted only simple hysteresis. The behavior of complex hysteresis was thought to be a result of the moderate mass transfer resistance coupled with the heterogenous reaction. That complex hysteresis disappeared at high flow rates illustrated that multiplicity also arises from the mass feedback mechanism inherent with backmixing in the continuously stirred tank reactor.
A discrepancy was found to exist between the reaction rate measured by the calorimetry and that given by the CO(,2) concentration measurement. That CO(,2) molecules escape "hot" from the catalyst surface was postulated to account for the above experimental observation. The suggestion of such thermal non-equilibrium behavior was in agreement with the current experimental report from other research groups. The non-equilibrium behavior should be taken into account in the mathematical model describing the reaction system. This, however, has so far not been done.
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