Improvement of a thermokinetic technique and its application to methanation mechanism studies



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Calorimetry has been recognized as a potentially valuable tool for studying fluid - solid catalytic interactions. Each step in a surface reaction proceeds with an exchange of heat. If the heat associated with each step can be separated, quantitative information for evaluating a mechanism would be available. The application of thermal techniques of analysis to the elucidation of surface mechanisms has been retarded by the unavailability of a thermal detector that would give representative heat values in the presence of position varying heats, and that would respond rapidly enough to separate the heats associated with reaction steps. A detector has been developed that will give representative thermal values, even with strong zoning adsorption or reaction mechanisms. It is also of utility as a thermokinetic device, having an order of magnitude faster time response than the so called "fast responding" thermal detectors. Its simplicity is also one of its merits. This improved thermal detector - termed a conduction, heat flow calorimeter - was applied to the study fo the hydrogenation of carbon monoxide on a nickel catalyst. Based on the thermal results obtained, it was concluded that the initial hydrogenation of adsorbed carbon monoxide, due to an equilibrium limited hydrogen adsorption was a rate limiting step. At low temperatures (less than 200 C) the dehydration of a partially hydrogenated C-O-H complex was also rate limiting.