TRANSIENT KINETICS OF METHANATION OVER UNSUPPORTED COBALT
Abstract
An apparatus to produce and characterize transient reaction conditions in a continuous flow catalytic reactor was developed. The response of CO hydrogenation to sudden changes in both reactant partial pressure and isotope composition was measured by a computer-driven mass spectrometer. Replacement of 3.3/1 H(,2)/CO by inert followed by H(,2) at 250(DEGREES)C produced transient rates of methanation several times the steady state rate. The water and methane yields during the hydrogen exposure indicated monolayer coverage of reactive material with an oxygen to carbon ratio of 1.2 at steady state. Substitution of ('13)CO for ('12)CO at steady state showed that surface CO was abundant and exchanged very rapidly with the gas phase. The ('13)CH(,4) response was consistent with reactive intermediates present in 0.11 monolayer coverage and forming methane by at least two routes. CO dissociation was found to be nearly irreversible but not rate-determining. Substitution of D(,2)/CO for H(,2)/CO at steady state produced large amounts of HD and indicated a very low hydrogen coverage. Equilibrium distribution of partially deuterated methanes was consistent with the timing but not the amounts observed. The HDO and D(,2)O responses indicated that OH is the dominant oxygenated intermediate and that surface oxygen is very rare.
Degree
Ph.D.
Subject Area
Chemical engineering
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