The kinetics of the palladium-catalyzed vapor-phase thermal decomposition of ethanol

The rate of thermal decomposition (190-231 degreesC) of ethanol on Pd/Al2O3 to yield CH4, CO, and H-2 has been studied in a tubular reactor at differe ntial conversion and in a Berty reactor. Ethanal is a byproduct that is als o present as an intermediate species formed in a dehydrogenation reaction. The presence of Ha is necessary in the decomposition of ethanal to suppress coking, and under these conditions, decarbonylation is faster than dehydro genation of ethanol. The differential rate data (206 degreesC) were fitted to a large number of alternative LHKW kinetic models. These effectively des cribe the relative strength of adsorption (C2H5OH approximate to CH3CHO > C O > H-2 > CH4), whereas discrimination between different kinetic pathways i n the surface reaction is difficult. Nevertheless, models that describe the adsorption of ethanol or its surface dehydrogenation perform well. Desorpt ion of Ha is not rate-limiting. In the modeling, the goodness of the fit is dependent on the number of kinetic constants, and they can be increased by elaboration of the mechanistic steps.