Theses studies revealed that the amount of adsorbed

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Unformatted text preview: decreased with increasing adsorption temperature (Fig. 29). Basing on these results TPD of CO2 after 15 hours adsorption at 100, 150 and 200°C was also performed for the samples Ni0C900, Ni30C900 and Ni72C900 chosen as samples with remarkably different basic properties (Ni free catalyst, catalyst with a medium Ni/Mg ratio and Mg free catalyst, respectively). The specific desorption amount for the catalysts determined at different adsorption temperatures are presented in Figure 30. At 100°C the order was Ni72C900 >> Ni30C900 > Ni0C900, whereas at 150 and 200°C the order was Ni0C900 » Ni30C900 >> Ni72C900. 104 3. Results and discussion - catalyst preparation and characterisation amount of desorbed CO 2 [mmol / g] 4 3 3h 2 15 h 1h 1 50 100 150 adsorption temperature [°C] 200 Fig. 29 Amount of desorbed CO2 after adsorption at different adsorption times (1, 3 and 15 hours) and temperatures (100, 150 and 200°C) for the catalyst Ni0C900 100°C 150°C 200°C 78 2 CO 2 desorbed [m mol / m ] 80 60 40 36 31 27 25 16 20 15 10 5 0 Ni0C900 Ni30C900 Ni72C900 catalyst Fig. 30 Specific desorption amount of CO2 of the catalysts calcined at 900°C determined by TPD of CO2 after 15 hours of adsorption at 100, 150 and 200°C 3. Results and discussion - catalyst preparation and characterisation 105 The results show that for the temperature programmed desorption of CO2 after adsorption for 1 hour at 100°C did not allow to differentiate between the catalysts. The experiments performed at different adsorption conditions show that CO2 desorption is influenced by adsorption time and temperature. Basicity expressed as specific adsorption amount after adsorption at longer time and higher temperature correlates well with the Mg content, but its values are too high compared to those reported in the literature for chemisorption of CO2 on MgO (1.45 – 4.4 µmol/m2) [116]. This may be due to the formation of a superficial carbonate layer or metal hydroxide groups resulting from incomplete removal of water from the CO2 feed stream. The reverse in the order specific desorption amount at 100°C compared to 150 and 200°C m...
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This document was uploaded on 10/07/2013.

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