On the use of the first-order approximation in the kinetic analysis of TPR profiles

A theoretical investigation was carried out on the analysis of TPR profiles by the power-law kinetic model. Attention was focused on the use of the first-order approximation, with the aim to assess its limits in the procedure for estimating the activation energy of reduction. Numerical simulations performed by solving the non-isothermal mass-balance equations for the gaseous and solid species indicated a high sensitivity of the reduction patterns to the reaction order with respect to the solid. This quantity was found to exert a considerable influence on both the temperature at peak maximum and the peak shape. A large number of TPR profiles was generated, assuming reaction orders other than unity and activation energies ranging from 80 to 100 kJ mol(-1). These profiles were interpreted by means of the first-order power-law model. The results obtained showed that the unjustified assumption of the first-order approximation may introduce significant errors in the estimate of the activation energy. In several cases, real and estimated values differed by more than 30%. In order to provide some guidelines for a correct kinetic analysis, the causes responsible for such misinterpretation were investigated from both a qualitative and quantitative point of view

Signal-dependent noise characterization for mammographic images denoising

Abstrac t – The paper deals wi th the no ise character iza t ion under the assumption of a he teroscedast ic signal –dependent no ise model in the context o f medical imaging. In par t icular, in this kind of applica t ion, a sophis t icated noise var iance es t imat ion algori thm is appl ied us ing robust es t imators and nonlinear regress ions. A direct rela t ion be tween no ise var iance and pixe l intensi ty values i s obtained and used wi thin a mul t ireso lut ion denoising algor i thm, performed by Wavelet Thresholding (WT). We wi l l provide result s o f the no ise es t imation, by app lying the proposed method to mammographic images. I

TEMPERATURE-PROGRAMMED REDUCTION IN CATALYSIS - A CRITICAL-EVALUATION OF THE METHOD

Temperature-Programmed Reduction (TPR) has been critically tested by carrying out experiments at different operating conditions on both copper-based catalysts and pure copper oxides (CuO, Cu2O). In this work we give experimental evidence that, even if interference caused by mass transfer limitations or dispersion is removed, the reduction profiles are markedly affected by artefacts when an inadequate combination of the typical TPR operating variables is used. Furthermore, an attempt of tracing back to the artefacts origin is also effected

REDUCTION KINETICS OF CUO-ZNO

Copper-containing catalysts are activated, before use, by a reduction process where the presence of ZnO has a promoting effect. The present paper deals with the kinetic behaviour of the reduction of the copper species in well defined specimens of CuO-ZnO. The effects of the temperature, hydrogen pressure and ZnO content on the consumption rate of hydrogen are analysed. A kinetic model is proposed which is consistent with the chemistry of the reduction reactions which involve the formation of the intermediate Cu+. The model appears to be able to describe the consumption rate of hydrogen and to account for the distribution of copper species in the course of the reduction