Partial oxidation of n-hexadecane at short contact times:: Catalyst and washcoat loading and catalyst morphology

Rhodium supported on alumina foam is an exceptionally active catalytic partial oxidation catalyst, giving high selectivities to syngas or olefins by changing reaction stoichiometry or catalyst properties such as rhodium loading and washcoat loading. Rhodium catalyst loading and gamma-alumina washcoat loading were varied systematically on a-alumina foams to investigate resulting microstructure and products of the partial oxidation of n-hexadecane. At conditions favorable for producing syngas, varying rhodium loading between 0.05 and 10.0 wt.% (a factor of 200) had little affect on H-2 and CO selectivities or fuel conversions. However, non-washcoated catalysts gave low selectivities to syngas. Increasing washcoat loading results in high selectivities of olefins, while varying rhodium loading has little affect on production of olefins. Selectivitiy data from multi-metallic catalysts, Rh-Ce and Rh-Pt, was also investigated. The morphology of catalysts was examined using scanning electron microscopy. The micrographs indicate that increasing rhodium loading above a few percent led to the formation of a rhodium film on the catalyst support. The presence of washcoat seems to keep rhodium spread on the surface at high reaction temperatures enhancing heterogeneous products. Very high washcoat loadings (10 wt.%) decrease pore diameters, increasing the likelihood of reactant contact with the rhodium surface, leading to increased H2 and decreased olefin selectivities. (c) 2006 Elsevier B.V. All rights reserved.