The whole scheme of carbon deposition in steam

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Unformatted text preview: g encapsulating carbon. In this case metal surface area is generally lost and the catalyst deactivates. The whole scheme of carbon deposition in steam reforming is depicted in Figure 3. The minimisation of coke in gas-solid depends on the reaction itself and on the particular catalyst. For example, as already pointed out above are noble metal catalysts much less prone to coking than Ni based catalysts in the steam reforming process. Concepts like the addition of basic promoters to the catalyst to minimise coke formation in the steam reforming and the CO 2 reforming over Ni catalysts have already been discussed above. 33 1. Introduction Adsorbed hydrocarbon Adsorbed CO Gasification Ca Cb Encapsulating carbon Solution of C in Ni Carbon whiskers Fig. 3 Scheme of the formation of carbon deposits during steam reforming 1.5. Catalytic partal oxidation i Though the catalytic partial oxidation of methane (CPOM) has not yet been used on an industrial scale the large number of publications and patents issued recently show the great interest in this process [10]. Research in this field has been focused almost exclusively on methane as feedstock. Different catalysts containing group VIII metals (group 8-10) and Cu were studied [9, 10, 22, 23, 65, 69, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112]. As in the steam reforming and the CO2 reforming, several noble metals, Co and Ni catalyse the reaction. Ni and Rh containing catalysts were found to be the most active catalysts for CPOM. 34 1. Introduction 1.5.1. Catalytic partial oxidation of methane over Ni catalysts The thermodynamic calculations show that in the partial oxidation of CH4, CO and H2 are the main products at higher temperatures, H2O and CO2 being the only considerable by products (Tab. 6) [9, 107]. Tab. 6: Approximate thermodynamic values of the CH4 conversion and selectivity of CO and H2 for a reaction mixture of CH4/O2/He (2/1/4) [9] 500°C 600°C 700°C 800°C 900°C CH4 conversion 28% 60% 83% 95% 98% CO selectivity 41% 65% 91% 96% 99% H2 selectivity 61% 81% 83% 97% 99% As in the steam reforming and the CO2 reforming Ni catalysts are also likely to be used for the partial oxidation of...
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