Furthermore the increase in the reaction temperature

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Unformatted text preview: orted by the fact that only at 900°C a decrease of the reaction temperature was observed. This may be due to homogeneous reactions leading to total oxidation products (H2O, CO2), e.g. oxidative cracking or total oxidation of C3H8 taking place before the feed stream gets into contact with the catalyst. Over the catalyst H2O and CO2 are reformed by not reacted C3H8 and this is reaction is highly endothermic. The different trend of Ni10C800 compared to Ni10C900 and Ni10C1000 with regard to catalyst deactivation and coking cannot be explained easily because for this catalyst structural changes like reconstruction must be taken into account. Comparing Ni10C900 and Ni10C1000 shows that Ni10C900 is more stable and has a higher resistance against coking, which is attributed to its lower crystallinity. Ni10C900 and Ni10C1000 are more stable and coke resistant at higher reaction temperatures, which was also found for the other catalysts in the catalyst screening. 4. Results and discussion - catalytic partial oxidation of propane 140 5. Conclusions 141 5. Conclusions Coprecipitation at low supersaturation at pH 8 ± 0.2 and 60-70°C resulted in the formation of Ni, Mg and Al containing hydrotalcite-type materials of the approximate formula [NixMg72-xAl28(OH)200][(NO3)y(CO3)(28-y)/2]· 50H2O (x = 0, 5, 1, 15, 3, 5, 72 and 11 ≤ y ≤ 16). Their thermal stability was found to decrease with increasing substitution of Mg2+ by Ni2+. By calcination at temperature • ƒ& LQ D IORZ RI DLU WKHVH VROLGV ZHUH WUDQVIRUPHG into their corresponding mixed metal oxides consisting of divalent metal oxide phases with periclase structure and spinel phases. At lower temperatures poorly crystallised divalent metal oxides and amorphous Al2O3 phases with poorly crystallised spinel at their interfaces were formed. The degree of crystallinity increased with increasing calcination temperature. Catalysts with a lower nickel content exhibited remarkably high surface areas suggesting that the remova...
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