The decrease in the conversion at a slightly higher

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Unformatted text preview: geneous reactions due to the presence of the solid phase. The further decrease upon adding the Ni free or the not reduced catalyst, both placed on a SiO2 wool bed, could have the same nature. The results also show that the SiO2 wool bed has no significant catalytic influence and is therefore suitable to hold the catalyst. Despite these effects the yields of CO and H2 over the active catalyst shall be compared to the yields observed for the empty reactor, the most effective set-up among all studied blank experiments (already presented in Figure 36 and 38). In the temperature range common to both configurations the yield could be increased by a minimum of factor 2 for CO and factor 8 for H2 by the use of the catalyst. At 650°C the non-catalysed reaction ceased, no more H2 and only very little amounts of CO were produced (Y < 1%), whereas in the presence of the active catalyst even at 600°C higher yields of CO and H2 were observed than at 1000°C in the empty reactor. In addition, the catalysed reaction yielded fewer undesirable side products. Over the catalyst the only observed side products were H2O, CH4 and CO2 as well as traces of C2H4 and C3H6 at 800°C. Without the catalyst considerable amounts of C2H4 and C3H6 and also traces of C2H2 and C3H4 were additionally produced. These unsaturated 123 4. Results and discussion - catalytic partial oxidation of propane ppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppppp products, especially the alkynes can cause severe problems in any downstream processes, e.g. by the formation of so-called green oil [126]. A more detailed further discussion of these different experiments is worthwhile as it can give valuable information and possibly a deeper insight into the reaction. In the blank experiments C3H8 and O2 are only effectively activated at high temperatures ( • ƒ&  whereas over the reduced Ni catalyst complete O2 conversions are achieved regardless the temperature and even at reaction temperatures as low...
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