Deactivation kinetics in the hydrogenation of nitrobenzene to aniline on the basis of a coke formation kinetics - investigations in an isothermal catalytic wall reactor
E. Klemm et al., Deactivation kinetics in the hydrogenation of nitrobenzene to aniline on the basis of a coke formation kinetics - investigations in an isothermal catalytic wall reactor, CHEM ENG SC, 56(4), 2001, pp. 1347-1353
The heterogeneously catalysed gas-phase hydrogenation of nitrobenzene to an
iline on an alpha -alumina supported palladium catalyst is a highly selecti
ve reaction which however is deactivated by coking. A catalytic wall reacto
r (CWR) was proved to be a powerful tool for the determination of a deactiv
ation kinetics on the basis of a coke formation kinetics. Nitrobenzene was
identified as coke precursor, whereas aniline had no influence neither on t
he kinetics of the nitrobenzene hydrogenation nor on the kinetics of coking
. The coking of the catalyst was investigated by monitoring axial coke prof
iles along the coated wall of the CWR with progressing time-on-stream. Anal
ysing the coke formation at the coated section close to the inlet allows a
fast determination of the fundamental dependencies of coke formation on par
tial pressures of reactants and on temperature. For the first coated sectio
n partial pressures correspond to the well-defined inlet values and do not
depend on time. Fitting coke profiles and the nitrobenzene outlet concentra
tions allowed the conclusion that it is indispensable to differentiate betw
een coke on the support and coke on the active site. Furthermore, both coke
on the support and coke on the active site were found to be responsible fo
r deactivating the hydrogenation of nitrobenzene. Thus, it was concluded th
at also the support is involved in hydrogenation of nitrobenzene due to hyd
rogen spillover. (C) 2001 Elsevier Science Ltd. All rights reserved.