Nanocrystalline Cu-Ce-Zr mixed oxide catalysts for water-gas shift: Carbon nanofibers as dispersing agent for the mixed oxide particles

Nanocomposite catalysts containing carbon nanofiber (CNF) and Cu-Ce-Zr mixed metal oxide (MMO) have been prepared by homogeneous co-precipitation with urea. The water-gas shift (WGS) reaction has been used as test reaction. The CNF-containing nanocomposite catalysts exhibit similar overall catalytic activity and stability as the corresponding CNF-free catalyst. Thirteen weight percent of the MMO could be replaced by CNF without decreasing the overall activity and stability of the catalyst. The specific activity of the nanocomposites based on the total metal oxide content is similar or higher than the activity of the CNF-free material, depending on the CNF content. Similar activation energies are, however, obtained for the CNF-free and CNF-containing materials. We cannot exclude that the CNF material acts as reaction promoter under certain conditions, but suggest that the impact of CNF addition on the precipitation of the mixed oxide particles, and hence the catalytic activity relative to the CNF-free MMO, should also be considered. CNF may be regarded as inert dispersing agent material improving the precipitation of the MMO under conditions where the co-precipitation of the MMO precursors does not result in materials with high surface area.