This was necessary as technical grade co2 was used

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Unformatted text preview: 1· cm-1· °C-1) respectively [122]. The other modification is that the CO2 stream was dried by a moisture trap containing silica gel. This was necessary as technical grade CO2 was used for the experiments. The colour change from blue (dry) to pink (hydrated) was used as indicator for the reactivation of the moisture trap. 2. Experimental 60 In the TPD-CO2 experiments a sample of 50 mg of each calcined catalyst was used instead of 5 mg like in the TPR experiments, because of the lower effect of the CO2 desorption on the detector signal. The samples were degassed up to 620°C in the flow of He. After desorption of contamination the sample was cooled down in a flow of He to the desired adsorption temperature (100-200°C). CO2 adsorption was performed in a flow of pure CO2 for 1, 3 or 15 hours. After the adsorption the flow was switched to He and the baseline was allowed to stabilise and adjusted to zero before performing the CO2 desorption up to 620°C at a heating rate of 10°C/min. 2.7. Test reactions for determination of basicity The transformation of isopropanol and the aldol condensation were performed using a simple catalytic reactor set up that consisted of the reaction feed system, the reactor and the analytical system. In the reactant feed system two mass flow controllers were used for controlling the gas flows. One was used for controlling the He flow passing through a saturator containing the liquid substrate (isopropanol, acetone, p.a., POCh, Poland), the other one to adjust the flow of He to dilute the saturated He stream or to control the flow of air. The saturator consisted of two parts. In the first part the He stream was saturated with the vapour of the liquid at room temperature by bubbling it through the liquid. To ensure a constant concentration of the vapour, in the second stage the gas stream was equilibrated at 0°C using a condensator cooled by a waterice mixture. To avoid condensation of less volatile products the tubing after the reactor was heated by heating tape. The quartz plug flow re...
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