The final result of further increase of the ghsv is

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Unformatted text preview: he activity of the catalyst decreases [107, 109]. The final result of further increase of the GHSV is the total oxidation of the catalyst and hence the loss of activity. The experiments performed by Schmidt et al. show clear tendencies for the influence of the CH4/O2 ratio, but it must be kept in mind that the reaction temperature was higher in the experiments with a lower CH4/O2 ratio. Due to the temperature differences it is difficult to determine in how far the higher CH4 conversions were due to the lower CH4/O2 ratio or to the higher reaction temperature. Increasing GHSV may result in the oxidation of the catalysts by the reaction mixture that is more oxidative due to the lower conversion of O2. 1.5.1.8 Stability of the catalysts Deactivation of Ni catalysts with time-on-stream was reported in several cases. Like in the steam reforming and the CO2 reforming the deactivation is due to the formation of carbon deposits [10]. Basile et al. tested Ni/Mg/Al containing catalysts derived from hydrotalcite-type precursors with varying Ni and Mg content [9]. They observed that the pure Ni/Al catalyst and the catalyst with a high Ni/Mg ratios (~ 6:1) deactivated very fast due to coking. The catalysts with a lower Ni/Mg ratio, 3:4 and 1:6 showed good stability, according to the authors these two catalysts showed no signs of deactivation 1. Introduction 44 ytrtrghrhrhhrhrhhfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff during 500 hours time-on-stream. The positive effect of Mg was also reported by Sokolovskii et al. who found that coprecipitated Co/Mg/Al catalysts with Co/Mg ratio of 1:1 and 1:3 were stable for hundreds of hours on stream [96]. Though coke formation is the main problem, also the oxidation of the Ni particles to NiO was reported to have a deteriorating effect on the conversion and the selectivities of the catalyst in CPOM as already discussed. These oxidised Ni catalysts can be further damaged due to sol...
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This document was uploaded on 10/07/2013.

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