Journal of Thermal Analysis and Calorimetry, Vol. 73 (2003) 851–858 ROLE OF THE HEAT-TRANSFER COEFFICIENT IN DETERMINING THE OVERALL ACTIVATION ENERGY OF THERMOKINETIC OSCILLATIONS N. I. Ionescu 1* , N. I. Jaeger 2 , P. J. Plath 2 , M. A. Liauw 3 and C. Hornoiu 1 1 Romanian Academy, “I. G. Murgulescu” Institute of Physical Chemistry, 202 Splaiul Independentei, 060041 Bucharest, Romania 2 Bremen University, Institute of Applied and Physical Chemistry, P.O. Box 330440, 28334 Bremen, Germany 3 Erlangen-Nürnberg University, Department of Technical Chemistry, Egerlandstr. 3, 91058 Erlangen, Germany (Received October 17, 2002; in revised form March 3, 2003) Abstract Thermokinetic oscillations obtained during the heterogeneous catalytic oxidation of methanol on Pd/LiAl 5 O 8 in a dynamic calorimeter were characterized by an overall activation energy. This pa- rameter was determined using the minimum and maximum values of the temperature oscillations. Using bifurcation diagrams with oxygen or methanol as bifurcation parameters. E values for all heat- ing loss laws were calculated which are within the range for heterogeneous catalytic oxidation reac- tions. The obtained results have been discussed. Keywords: heat loss, overall activation energy, thermokinetic oscillations Introduction Oscillatory behavior of the heterogeneous catalytic oxidation of methanol on sup- ported palladium catalysts is now well established [1–9]. The highly exothermic catalytic oxidation of methanol on Pd/LiAl 5 O 8 (Bayer) was monitored by recording the catalyst temperature T vs. the temperature of the reactor T R , ∆T=T–T R this corresponds either to a steady state rate of reaction or to the dynamic behav- ior of the system, e.g. in the case of observed thermokinetic oscillations. In a previous paper [10] we have considered the temperature oscillations like a non-isothermal process in which the necessary energy for the thermokinetic oscillations is brought not from outside, but from inside, by the exothermic process of oxidation it- self. Using the minimum and maximum values of the oscillations temperature we have obtained a heat balance equation in which the heat-transfer coefficient was assumed to be temperature independent. With this model we were able to obtain the overall activation energy of a heterogeneous catalytic reactions in oscillatory regime [10]. 1388–6150/2003/ $ 20.00 © 2003 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: ionescu@chimfiz.icf.ro