Journal of Thermal Analysis and Calorimetry, Vol. 67 (2002) 597–603 SOME CRITERIA FOR DECIDING UPON THE SUPPORT EFFECT T. Vlase, G. Jurca and N. Doca Department of Chemistry, West University of Timiºoara, Str. Pestalozzi 16, RO-1900 Timiºoara, Romania (Received April 18, 2001; in revised form September 27, 2001) Abstract Criteris for deciding upon the support effect by the thermal decomposition of precursor/support sys- tems are discussed. Instead of the linear relationship between lgA and E, two new criteria determined by the calculated rate maximum were suggested. Dimensionless criteria based on the rate, conver- sion and temperature values at the inflexion point of the TG diagram lead to a parameter able to de- scribe the support effect in a synthetic and quantitative manner. The experimental data were the TG-curves for the decomposition of ammonium metavanadate, molybdic acid and ammonium phos- phomolybdate, supported on carborundum and silica. Keywords: dimensionless parameters, discrimination possibilities, non-isothermal kinetics, sup- ported precursors, support effect Introduction In non-isothermal kinetics, the compensation effect, i.e. the variation in paralell of E (activation energy) and lnA (pre-exponential factor) is a rather ‘normal’ phenomenon [1]. By the thermal decomposition of a certain substance deposited on a certain sup- port, the pair values of E and lnA for different concentrations of deposited substance presents the above-mentioned parallelism. In such cases the compensation effect is assigned to a ‘support effect’ [2, 3]. The present paper deals with argumentations and critical analysis of some crite- ria for deciding upon a support effect. The suggested criteria were obtained by an ad- equate processing of the TG-curves, the first and essential step being the determina- tion of the non-isothermal kinetic parameters, i.e. the activation energy, pre-expo- nential factor and reaction order, respectively. The next step is investigating the com- pensation effect and the corresponding discussion upon the magnitude of the support effect. In a previous work [4] on the thermal decomposition of some catalyst precur- sors, the support effect was estimated by the difference of the isokinetic temperature between a supported and a mechanical mixture of a precursor/support pair having the 1418–2874/2002/ $ 5.00 © 2002 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht