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Unformatted text preview: h increasing crystallinity of the catalysts.
The partial oxidation of C3H8 to syngas (CO + H2) could be successfully performed at
temperatures between 600°C and 900°C over reduced Ni containing catalysts. CO and H2 were
the main products, H2O, CO2 and CH4 the only considerable side products. The conversion of
C3H8 and the yield of syngas increased with increasing reaction temperature. Unreduced Ni
exhibited no specific catalytic activity. The catalysts with a low to medium Ni content exhibited
better catalytic performance than those with a higher Ni content or the reference catalyst
(conventional steam reforming catalyst, 20 wt% NiO/Al2O3 + 2 wt% K2O). Coking was found
to decrease with increasing reaction temperature and to increase with increasing Ni content. No
clear relation was observed between coking and catalyst deactivation. So it was concluded that
different types of coke could be formed over the catalysts of which not all were deactivating.
Since several factors characterising the catalysts (BET surface area, Mg content and available
Ni surface) follow the same or the opposite trend with the Ni content, so it was impossible to
differentiate between these properties and their effect on the catalyst performance or coking. The catalyst with an approximate metal composition Ni10Mg62Al28 calcined at 900°C exhibited
the best catalytic performance, a good stability with time-on-stream and a high resistance
against coking (the highest at 800°C). The partial oxidation of propane performed over this
catalyst compared with the results of the non-catalytic reaction showed at least two-fold
increase in the yield of CO and eight-fold increase of the H2 yield.
Studies of O2/C3H8 feed ratio and the space velocity revealed that the total C3H8 conversion was
only achieved in excess of O2 because even under O2 deficient conditions part of the O2 leads to
the total oxidation products CO2 and especially H2O. Coking showed no dependence on the
O2/C3H8 feed ratio. Under O2 deficient conditions only sma...
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