Authors:A. Coelho, I. Moreira, J. de Araujo, and M. de Araujo
The57Fe Mössbauer spectra of substituted pentacyanoferrate /II/ complexes [/CN/5 FeII L]3– have been obtained for L=adenine, guanine, purine, caffeine, ethylene sulphide, dimethyl sulphoxide, and ammonia. The Mössbauer parameters are utilized to classify the various ligands according to their and bonding abilities. A linear correlation between the Mössbauer isomer shift and the tetragonal distortion caused by the ligand L is proposed. Comparison between this linear correlation and the approximative method of Wentworth and Piper1 is made.
HZSM-5 zeolite was screened as catalyst for high density polyethylene degradation at 450‡C, under nitrogen static atmosphere.
Two different samples were studied in this condition: HDPE alone and mixed with HZSM-5. The reactor was connected on line
to an HP 5890-II gas Chromatograph. Sample degradation was investigated using a Perkin-Elmer Delta 7 Thermobalance, from room
temperature to 800‡C, with heating rates of 5.0, 10.0 and 20.0‡C min−1. From TG curves, the activation energies, calculated using an integral kinetic method, decreased 60.6% in the presence of
The SiMCM-41 mesoporous molecular sieve was synthesised by the hydrothermal method. The physicochemical characterisation by
infrared spectroscopy, X-ray diffraction and thermogravimetry, showed that the material presents a well-defined structure.
In this study, the determination of the total acidity and relative strength of the acid sites of the SiMCM-41,was performed
by desorption of adsorbed n-butylamine combined with thermogravimetric measurements. The total acidity, determined by means of the amount of amine desorbed
normalised by mass of solid, was equivalent to 0.927 mmol g–1, in the temperature range from 96 to 235°C. By using the Flynn and Wall integral kinetic model, at 5, 10 and 20°C min–1 heating rates, it was determined that the activation energy to desorb n-butylamine was 90.7 kJ mol–1, in the same temperature range, evidencing that SiMCM-41 presents only weak acid sites on its surface.
Authors:A. de Araujo, V. Fernandes, and G. Fernandes
The acid properties of the Ca/NaY zeolite were investigated by means ofn-butylamine desorption and thermal decomposition, using both thermogravimetry (TG) and differential scanning calorimetry (DSC).
The total acidity of the zeolite was calculated from the TG data, while DSC was used with the Borchardt-Daniels kinetic model
to determine the relative acid strength of the catalyst, given in J per acid site. The enthalpies of these processes are proportional
to the acid site strength in each specific temperature range.
The use of catalysts in numerous important processes is widespread throughout the chemical and petroleum-processing industries.
Thermal analytical techniques can be used to evaluate important properties and processes associated with solid catalysts.
This paper presents examples carried out in our laboratory of the general application of TG and DSC to the acidity, activity
and regeneration of solid catalysts.
A thermogravimetric method is proposed for study of the kinetic parameters of coked HZSM-5 zeolite regeneration. The technique,
which makes use of integral thermogravimetric curves, was optimized by microprocessed integrated mathematical methods. The
kinetic parameters obtained from the TG curves are the activation energy, the rate constants, the half-life times, and in
particular the coke removal time as a function of temperature. The activation energy calculated by using the Flynn and Wall
kinetic method was 81.4 kJ mol−1. It was observed that, to remove 99% of the coke from the zeolite in a period of 1 h, it would be necessary to carry out
thermo-oxidation at 748 K, with a dry air purge flow of 120 cm3 min−1.