TAP REACTOR STUDY OF THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE USING AN INDUSTRIAL FE-CR-MO OXIDE CATALYST

The mechanism and kinetics of methanol oxidation to formaldehyde on an industrial Fe-Cr-Mo catalyst have been investigated using the TAP (te mporal analysis of products) reactor. The Mars-van Krevelen redox mech anism of partial oxidation was confirmed. By kinetic isotope experimen ts, the abstraction of hydrogen from the adsorbed methoxy intermediate was found to be the slow step on the catalyst surface. Water was obse rved to readsorb strongly on the catalyst, thus explaining the reduced rate of reaction that has been found at high methanol conversions. We aker readsorption of formaldehyde was observed. The kinetics of the re action were studied on a fully oxidized and a partially reduced cataly st. On the fully oxidized catalyst, the activation energy for formalde hyde formation was estimated to be 87 kJ/mol. At 360 degrees C the ave rage surface residence time of the adsorbed species in the conversion of methanol to formaldehyde was approximately 40 ms, meaning that the surface reaction rate constant for the main reaction is 25 s(-1). The surface residence time was significantly longer on the partially reduc ed catalyst, indicating a much slower surface reaction rate constant a nd emphasizing the importance of oxidation state on the rate of formal dehyde formation.