The hts are afterwards calcined together with the

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Unformatted text preview: y precipitated onto the support. The HTs are afterwards calcined together with the support yielding the supported mixed metal oxide catalyst. The second method is deposition-precipitation on preformed pellets of theta and gamma alumina, successfully applied in the synthesis of Ni/Al catalysts [66]. Pellets of alumina are impregnated with a solution containing only of the M(II) salt. An initially high pH value is used to dissolve part of the aluminium ions of the support, e.g. as [Al(OH)4]-. This way the support provides the aluminium ions, which then react with the M(II) ions of the solution, forming HT phases on the support surface and inside the pores upon lowering the pH value. Noteworthy, that this method was not successful using alpha alumina pellets, which has been attributed to the low surface area and the stability of this support material against hydroxide ions. 1.3. Production of hydrogen and syngas using hydrocarbon feedstock Industrial processes designed to produce hydrogen or syngas are mainly based on the conversion of hydrocarbons to syngas a mixture of CO and H2 with steam (Eq. 4), or with oxygen (Eq. 5). On a much smaller scale also CO2 reforming of methane is used (Eq. 6). Steam reforming and CO2 reforming are highly endothermic processes, whereas the partial oxidation is slightly exothermic. To maximise the production of hydrogen or to adjust the CO/H2 ratio the reversible water gas shift reaction is used (Eq. 7). As hydrogen and syngas are produced in the same manner their production processes will be discussed together. CxHy + x H2O → x CO + (x+½y) H2 (∆H°298 = +260 kJ/mol for CH4) (Eq. 4) CxHy + x O2 → x CO + ½y H2 (∆H°298 = -36 kJ/mol for CH4) (Eq. 5) 23 1. Introduction CH4 + CO2 → 2 CO + 2H2 (∆H°298 = +247 kJ/mol) (Eq. 6) CO + H2O → CO2 +H2 (∆H°298 = +2.8 kJ/mol) (Eq. 7) The production of syngas using coal as feedstock was discovered already at the end of the 18th century [68]. Coal gasification is a well-established commercial technology. Modern processes for th...
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This document was uploaded on 10/07/2013.

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