Oscillatory oxidation of carbon monoxide over Pt, Pd, and Ir catalysts: a kinetic model

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1982

OSTI ID:6264258

Turner, J E

Oscillations in the rate of CO oxidation are studied over catalysts of Pt, Pd, and Ir. Measurements performed within a flow reactor system near atmospheric pressure establish the phenomenology of oscillatory behavior as a function both of gas temperature (T/sub g/) and the ratio of reactant partial pressures (P/sub CO/P/sub O/sub 2//). It is demonstrated that the oscillations occur between two branches of a Langmuir-Hinshelwood reaction mechanism. These branches are predicted from an analysis of steady state reaction kinetics, which examines the time rate of change of two quantities; the fractional coverage of chemisorbed oxygen (theta/sub 1/) chemisorbed carbon monoxide (theta/sub 2/) on the catalyst surface. A time dependent model is proposed for the oscillations in which the alternate formation and reduction of a more stable surface oxide induces transitions between these two branches. Utilizing estimated values of kinetic rate parameters and fitted values of oxide formation and reduction rates, excellent agreement is found between this model and the observed oscillatory characteristics. Independent measurements of the rates of oxide formation (k/sub ox/) and CO reduction (k/sub r/) over these metals are carried out on powdered polycrystalline samples in a modified microbalance system. These processes are examined in an extension of the oscillatory model which assumes that the total oxide formed (O/sub 3/) is distributed uniformly over X layers near the catalyst surface. Predicted functional forms from this analysis show good agreement with experimentally obtained oxidation and CO reduction isotherms.

• OSTI ID: 6264258
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
IRIDIUM
KINETICS
MATHEMATICAL MODELS
METALS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PLATINUM
PLATINUM METALS
REACTION KINETICS
TIME DEPENDENCE
TRANSITION ELEMENTS