Collect. Czech. Chem. Commun.
2008, 73, 1132-1148
https://doi.org/10.1135/cccc20081132
Kinetics of Reduction of Cu Ions in MFI Zeolite Investigated by H2-TPR Method
Roman Bulánek* and Pavel Čičmanec
Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, nám. Čs. legií 565, 532 10 Pardubice, Czech Republic
Abstract
The temperature programmed reduction with hydrogen (H2-TPR) profiles of the Cu-MFI zeolite matrix were measured. The effect of the Cu ions loading and the heating rate on the H2-TPR profiles was investigated. The obtained TPR profiles were evaluated by different methods in order to obtain kinetic parameters and the reduction process mechanism. It was observed that the results given by convenient methods based on the simple power-law kinetics cannot be used for evaluation of at least the reduction of monovalent copper. Based on the reaction rate dependence on the degree of conversion, an autocatalytic reaction mechanism model was suggested for monovalent copper reduction. The autocatalytic effect was ascribed to nanoclusters of metallic copper, which is formed during the reduction. The parameters of this model were obtained by fitting the reaction rate equation to experimental data. The simulated TPR profiles well describe the position and relative height of peaks in experimental TPR profiles. Using our approach to evaluation of kinetic parameters we found the activation energies for reduction of Cu2+, direct reduction of Cu+ and autocatalytic reduction of Cu+ equal to 91, 67 and 38 kJ mol-1, respectively. All the mentioned processes are controlled by the kinetics of order ca. 1.5.
Keywords: Copper; Reduction; H2-TPR; Zeolite; MFI; ZSM-5; Cu; Kinetics; Kissinger method; Iso-conversion Friedman method; Malek method.
References: 42 live references.
