161 methodology in order to find an optimal catalyst

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Unformatted text preview: mechanism is still under discussion. 1.6.1. Methodology In order to find an optimal catalyst and to study the influence of the Ni and Mg content a set of Ni/Mg/Al catalysts was prepared derived from hydrotalcite-type precursors. The hydrotalcite-type precursors were prepared by coprecipitation at low supersaturation at constant pH as it is regarded in the literature as the most successful method of synthesis. The Ni and Mg content ranged from pure Mg/Al to pure Ni/Al. The Al content was kept constant as it can only vary in a narrow range (25 – 33 metal atom%). Extensive characterisation of the physicochemical properties of the as prepared HT materials was performed by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES) for the determination of the metal composition, C and N analysis to measure the amount of CO32-, NO3-, thermogravimetry coupled with mass spectroscopy (TG-MS) to determine the amount of intercalated H2O, X-ray powder diffraction (XRD) for the phase composition, TG-MS and differential scanning calorimetry (DSC) for the analysis of the thermal degradation process of the HTs. The as-synthesised hydrotalcite-type solids were then transformed into mixed metal oxides by calcination at 900°C using a slow heating program and under a constant stream of air for the fast removal of the volatile decomposition products. 900°C was chosen as calcination temperature for three reasons. Firstly, because in the catalytic partial oxidation of CH4 rising the reaction temperature above 800°C had no significant 1. Introduction 47 ytrtrghrhrhhrhrhhffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff influence anymore. Since CH4 is thermodynamically more stable at higher temperatures than C3H8 and also more difficult to activate [113], 800°C was also regarded as the highest reasonable reaction temperature for the partial oxidation of C3H8. As the partial oxidation of C3H8 is an exothermic reaction, a possible overheating of the catalyst surface at l...
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This document was uploaded on 10/07/2013.

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