This procedure consisting of filtration and

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Unformatted text preview: e of the filtrate with each washing cycle were used to monitor their removal. This procedure consisting of filtration and suspension was repeated until the pH value of two consecutive filtrates did not change. In all synthesises 3 washing cycles were necessary. After the final filtration the resulting solids were dried at 100°C for about 24 hours. 2.2. Preparation of the catalysts The dried hydrotalcite-type solids were transformed into metal oxides by calcination in a tubular furnace (Barnstead Thermolyne, USA). The furnace consisted of an innermost segment with a heat stability of ± 0.2°C, according to the producer. The quartz boat was placed in this innermost segment allowing uniform calcination conditions. The catalysts were calcined at the desired temperature (700-1000°C) for 16 hours. The furnace was heated up and cooled down by a temperature ramp of 10°C/min. During the calcination a constant flow of air, generated by a water pump, 2. Experimental 55 fffffffffffffffffffffffffffffffffffffffffffgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff through the furnace was maintained. The hydrotalcite-type solids were powdered before the calcination to allow an even calcination and to assist the fast removal of the gases evolved during the calcination process. The use of the catalyst as a fine powder as received after the calcination process can lead to the blockage of the reactor due to the too fine particles, therefore larger particles must be used. However to avoid local variations of the velocities in a plug flow reactor (inner diameter 4mm) the reactor diameter should be at least 10 times larger than the particle size [121]. In order to fulfill these criteria the catalyst powder obtained after the calcination process was pressed at 5 bar and the resulting pellet crushed and sieved. The sieve fraction 0.2-0.385 mm was used. A conventional steam reforming catalyst prepared by the ‘Institute of Fertilisers’ in 3XáDZ\ 3RODQG ZDV XVHG DV D UHIHUHQFH FDWD...
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