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    Acidity of silica-alumina catalysts by amine titration using Hammett indicators and FT-IR study of pyridine adsorption
    (Scientific Technical Research Council Turkey, 1999) Yurdakoç, M; Akçay, M; Tonbul, Y; Yurdakoç, K
    In this study, characterization and surface acidity of Siral (SiO2-Al2O3) compounds were investigated with Hammett acidity functions, the n-butylamine titration method and FTIR analysis of the spectra of pyridine adsorption. All the samples had an acid strength of H-0 less than or equal to +2.8. The calculated total amount of acid of the samples increased with the increase in SiO2 content up to Siral 40 and then decreased sharply in the case of Siral 80. Maximum amount of acidity was observed in the case of Siral 40 as 1.37mmole/g. No evidence was found for a band at 1540 cm(-1) on Pural indicating that there were no Bronsted sites on the surface strong enough to react with pyridine. As a result, we can say that the Lewis sites predominate in all the silica-aluminas.
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    FTIR study of the adsorption of ammonia and pyridine on V2O5/MgO catalysts
    (Marcel Dekker Inc, 1998) Akçay, M; Yurdakoç, M; Tonbul, Y; Yurdakoç, K; Hönicke, D
    The adsorption of ammonia and pyridine on the surface of the V2O5/MgO catalysts has been studied for the determination of the Bronsted and Lewis acid sites. The data showed that the catalysts have medium Lewis acidity, but are also weak Bronsted acids, having active hydroxy groups able to interact with pyridine by H-bonding and by protonation. Pyridine is a suitable basic probe for the quantification of the catalysts. 32% V2O5/MgO catalyst is the most acidic catalyst.
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    Pyrolysis kinetics and chemical composition of Hazro coal according to the particle size
    (Springer, 2005) Duz, MZ; Tonbul, Y; Baysal, A; Akba, O; Saydut, A; Hamamci, C
    The relationship between particle size and chemical composition of Hazro coal (origin: SE Anatolia, Turkey) has been examined by elemental analysis and by thermogravimetric pyrolysis. The chemical composition of the coal was determined by grinding sample particles physically and separating according to their size in mm by sieving. Particle size distribution of the coal and chemical composition of these fractions were given. The coal has been non-isothermally pyrolysed in a thermogravimetric analyser to determine the kinetic factors. Thermal gravimetric (TG/DTG) experiments were performed from ambient temperature to 800 degrees C under a nitrogen atmosphere at heating rate 10 K min(-1) with five different particle size ranges. Kinetic parameters of the samples were determined using a Coats and Redfern kinetic model, assuming a first-order reaction. Depending on the particle size of the coal samples, the mean activation energy values varied between 49.1 and 84.6 kJ mol(-1). The results discussed indicate that activation energies increase as the particle size decreases.
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    Thermogravimetric investigation of the dehydration kinetics of KSF, K10 and Turkish bentonite
    (Scientific Technical Research Council Turkey, 2001) Tonbul, Y; Yurdakoç, K
    The kinetic parameters for the dehydration of bentonite from Turkey, KSF and K10 were determined by using dynamic TG techniques. The Ozawa method is better for the dehydration of the clay samples than the first order equation of Coats and Redfern. The former function calculates consistently higher activation energies than the latter. The mean values of the activation energies in the alpha range 0.1-0.7, are 56-66 kJ mol(-1) in the Ozawa method.