The process of desorption of a gas from a catalyst surface, especially when temperatureprogrammed, can be affected by the occurrence of other chemical or physical processes.On the basis of a simple method of analysis, which makes possible the examination of definite fractional areas of a peak, and therefore the examination of definite ranges of surface coverage during desorption, this paper examines two experimental cases of temperature-programmed desorption, relating to propylene metathesis on the practical catalysts, WO3/SiO 2 and Re20-//AI20 3.Some particular methods and procedures for collecting TPD data and obtaining reliable kinetic results in the presence of multiple peaks, and therefore in the case of the overlapping of other physical phenomena, are developed: the results on the adsorptive and desorptive properties of the two catalysts are compared with the results reported in the literature, obtained from kinetic studies concerning propylene metathesis on the same catalysts.Among the techniques for investigating and characterizing practical catalysts, temperature-programmed desorption (TPD) has become widespread in recent years. However, the obtaining of information on the nature of the interactions between adsorbed species and a catalyst surface requires the determination of reliable kinetic parameters and, in spite of the simplicity of the method, TPD spectra can be affected by many experimental factors (surface heterogeneity, diffusional resistances, desorption with readsorption or with reaction) in addition to those problems which derive from the use of a non-isothermal technique.Many desorption processes are very complex and require a careful choice of the experimental conditions in order to obtain meaningful results: TPD is a typical nonisothermal method and has retained the "philosophy" of flash desorption, from which it was derived. However, much attention must be paid to the heating rate, the sample mass, the adsorption temperature and the carrier gas flow rate, which not only influence the occurrence of heat and mass transfer limitations and readsorption, mass transfer limitations and readsorption, but also determine the possibility of overlapping or separation of different desorption processes.Many methods have been suggested [1][2][3], as far as the analysis procedure of the TPD spectra is concerned, to overcome these difficulties and to relate the kinetic parameters unambiguously and reliably to the rate-limiting process.
