Qin et al compared the various reforming reactions

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Unformatted text preview: o activate than O2, according to the authors. Qin et al. compared the various reforming reactions with the partial oxidation but did not account for the higher reaction temperature in the partial oxidation, due to the exothermic reaction(s). Hence their conclusion that the direct partial oxidation is the predominating reaction is not conclusive, as the higher CH4 conversions in the CPOM might be due the higher reaction temperature. For the same reason the correlation of the strength of the M-O bond and the activity of the catalyst in the CPOM is also not completely reliable. Furthermore the authors performed temperature programmed reactions only for the Rh catalyst but assumed that the result, similar onset temperatures for all the different reactions, is valid for all catalysts. 1.5.1.5. Activation of the catalyst Reduction is necessary to activate the Ni catalysts in the CPOM. Dissanayake et al. [107], Looji et al. [109, 110] and Nichio et al. [108], observed in CPOM over unreduced Ni catalysts below 700°C no complete conversion of O2 and very low conversions of CH4. The reactions products were exclusively CO2 and H2O. Upon rising the reaction temperature to about 700°C all three observed a sudden sharp increase in the CH4 conversion and almost complete O2 conversion, the products were now predominantly CO and H2. CO2 and H2O the only considerable side products. The behaviour was 1. Introduction 40 ytrtrghrhrhhrhrhhffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff comparable to the catalysts that were reduced prior to the reaction. Therefore the great enhancement of the catalytic activity was attributed to the reduction of the catalyst under the reaction conditions. This was also backed by Dissanayake et al. who observed that the composition of the catalyst bed was comparable to that of the catalyst reduced prior to the reaction under the same reaction conditions. Consequent decrease of the temperature had no effect on the O2 conversion and let to a moderate decrease in the CH4 conversion and the selectivities toward...
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This document was uploaded on 10/07/2013.

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