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Unformatted text preview: id state reactions of NiO with the support. Choudhary et al. and Torniainen et al. reported the formation of NiAl2O4 and NiSiO3 for Ni catalysts on alumina and silica, respectively, under the conditions of CPOM at higher temperatures [93, 105, 106]. Both compounds were reported to be inactive in CPOM and are more difficult to reduce than NiO, thus causing severe damage to the catalyst. Choudhary et al. reported that it was possible to avoid the formation of NiAl2O4 and NiSiO3 by precoating the support with different alkaline and rare earth metal oxides (MgO, CaO, SrO, BaO, Sm2O3 and Yb2O3) and calcining the precoated support prior to the impregnation with NiO [105, 106]. They found distinct differences in the CH4 conversions and selectivities to syngas depending on the precoating agent. MgO precoated catalyst exhibited the best results and SrO and BaO the worst. On the basis of the results of the temperature programmed reduction (TPR) of the different precoated catalysts they claimed that sintering of the Ni particles was responsible for the differences in the activities. MgO precoated catalyst showed the lowest degree of reduction, but the highest degree of Ni dispersion after reduction. The authors attributed the stronger resistance of the MgO precoated catalyst against reduction and sintering to the formation of a solid NiO-MgO solution. 1.5.2. Catalytic partial oxidation of higher hydrocarbons In contrast to the catalytic partial oxidation of methane only very limited work has been presented concerning the catalytic partial oxidation of hydrocarbon feedstock other 1. Introduction 45 ytrtrghrhrhhrhrhhffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff than methane. Schmidt and his co-workers have performed most of the work. They investigated the partial oxidation of the C2-C6 alkanes [20, 21, 22, 23]. Their studies have been limited to Pt, Rh and Pd containing monoliths using different carbon/oxygen ratios and various GHSVs under autothermal conditions, hence the reaction temper...
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This document was uploaded on 10/07/2013.

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