OSC Measurements at High Frequency

The apparatus used for these experiments was dedicated to the study of the CO+O2 reaction which was carried out under transient conditions at any given frequency close to 1 Hz. This system consists in two parts the gas manifold and the mass spectrometer. The global experimental setup is schematized on Fig. 7.8. 

Reactants (CO and O2) flows are regulated using mass flow controllers. Before the reactor entrance, reactants were mixed with a l%Ar/He carrier gas (100 cm. min ). Any kind of CO/(l%Ar/He) and 02/(l%Ar/He) mixtures could be obtained. For this study 2%CO and 1%02 mixtures were used. Reactant injections were controlled using automated injection valves. Alternate CO and Oj injections may take place at a frequency as high as 1 Hz. To optimize the response time, the dead volume was reduce to less than 2.5 cm, including the whole reaction circuit from the automated valve up to the capillary tube before the mass spectrometer. 

The catalyst, diluted in cordierite, is placed in a straight Pyrex reactor and pretreated under pure helium at 450°C (ramp rate = 2°C.min ) for 15 minutes. Reactions are carried out at 450°C. Experiments consist in 5 different steps, as presented on Fig. 7.9. 

The Ar signal is used as a reference to deduced the dead volume of the reactor 

The evolution of the gas phase composition is followed by mass spectrometry. Masses m/e = 4 (He), 28 (CO), 32 (O2), 44 (CO2) and 40 (Ar) are monitored every 0.1 second All the results presented below will be expressed per gram of solid. 

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Figure 7.8. Experimental setup used for OSC measurements at high frequency.

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