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The reverse in the order specific desorption amount

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Unformatted text preview: ay result from the lower stability of the superficial species formed in the case of Ni72C900. Determination of basicity by catalytic test reactions As a research method complementary to TPD of CO2 two catalytic test reactions were employed for the characterisation of the catalysts’ basicity. As the first test reaction the transformation of isopropanol was performed over selected catalysts (Ni0C900, Ni30C900 and Ni72C900) in the temperature range 200 - 280°C. In this reaction formation of propylene by dehydration of the alcohol over acid sites is observed, whereas on basic sites dehydrogenation of the isopropanol to acetone takes place. The results show a large increase of the catalysts’ activity in the conversion of isopropanol with increasing Ni content and also high selectivity towards acetone for all the catalysts (Fig. 31). This indicates that apart from the basic sites also Ni2+ ions possess considerable activity in the dehydrogenation of isopropanol to acetone [116]. The contribution of the basic magnesium sites in the overall activity is small therefore it ppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppp 106 3. Results and discussion - catalyst preparation and characterisation ppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppp was not possible to compare the catalysts with respect to their basicity basing on the results of these catalytic tests. 15 conversion [%] Ni72 10 Ni30 Mg72 5 0 190 selectivity towards acetone [%] 100 220 250 280 310 Ni72 90 Mg72 80 Ni30 70 190 220 250 280 310 temperature [°C] Fig. 31 Conversion of isopropanol and selectivity towards acetone over the catalysts calcined at 900°C 3. Results and discussion - catalyst preparation and characterisation 107 As another test reaction, the aldol condensation was studied over the catalysts Ni0C900, Ni30C900 and Ni72C900 in the temperature range 270 – 310°C. Formation of α,β -unsaturated carbonyl compounds catalysed by basic sides, was observed. Due to t...
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