Ds. Lafyatis et al., TAP REACTOR STUDY OF THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE USING AN INDUSTRIAL FE-CR-MO OXIDE CATALYST, Applied catalysis. A, General, 120(1), 1994, pp. 85-103
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.