Autothermal catalyst formulations

Giroux et al. and Farrauto et al., from Engelhard, presented a proprietary catalyst formulation for autothermal reforming, whicii was actually composed of a layer of platinum/rhodium steam reforming catalyst covered with a platinum/pallachum partial oxidation catalyst [57,107]. The catalyst was capable of reforming natural gas. 

Kolb et al. performed catalyst development in microchannel reactors for auto-thermal reforming of isooctane. Rhodium, nickel, ruthenium and palladium catalysts supported by zirconia and alumina were tested [73]. Rhodium on alumina turned out to be the most active catalyst, which also showed lowest selectivity towards methane. The rhodium content was then varied from 0.1 to 2 wt.% 1 wt.% rhodium on alumina was considered to be the optimum catalyst formulation with respect to both performance, stability and cost. A minimum S/C ratio of 3.3 was required to prevent coke formation. The catalyst was incorporated into an autothermal reforming reactor of kilowatt size (see Section 7.1.2). 

Avd et cd. investigated combined catalytic combustion and steam reforming but also quasi-autothermal reforming of methane in fixed catalyst beds. Two different catalyst formulations were used to combine the combustion reaction with steam reforming, namely a nickel catalyst for steam reforming and a platinum catalyst for methane combustion. The two catalysts were assumed to be placed into two serial... 

The results of Avd et al. are interesting because oxidation and steam reforming readions are separated through the assumption that they take place over different catalysts. However, in a practical fuel processor system, a single catalyst formulation would be used for autothermal reforming at least in the smaller scale. 

Methane or natural gas steam reforming performed on an industrial scale over nickel catalysts is described above. Nickel catalysts are also used in large scale productions for the partial oxidation and autothermal reforming of natural gas [216]. They contain between 7 and 80 wt.% nickel on various carriers such as a-alumina, magnesia, zirconia and spinels. Calcium aluminate, 10-13 wt.%, frequently serves as a binder and a combination of up to 7 wt.% potassium and up to 16 wt.% silica is added to suppress coke formation, which is a major issue for nickel catalysts under conditions of partial oxidation [216]. Novel formulations contain 10 wt.% nickel and 5 wt.% sulfur on an alumina carrier [217]. The reaction is usually performed at temperatures exceeding 700 °C. Perovskite catalysts based upon nickel and lanthanide allow high nickel dispersion, which reduces coke formation. In addition, the perovskite structure is temperature resistant. 

It must be noted, however, that efforts have been spent by several research groups with the aim of combining the favourable features of monolithic catalysts operated under autothermal conditions (thus favouring the onset in the gas-phase volumes of selective oxidation paths of the alkane fuel), with the development of intrinsically active and selective formulations able to contribute directly or indirectly to the selective production of olefins. A specific mention is deserved by rare earth oxides-based catalysts wherein contributions of the catalyst surface to the formation of ethyl species were reported. " Interestingly, through a detailed comparison of the observed performances of Pt-based and LaMnOs-based monoliths in ethane ODH experiments, Donsi et observed that the use of the perovskite-coated monolith yielded an improvement in ethylene yield. An overview of their results is reported in Fig. 28.6. 

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