On the selection of the best polymorph of Al2O3 carriers for supported cobalt nano-spinel catalysts for N2O abatement: an interplay between preferable surface spreading and damaging active phase–support interaction

Abstract

A series of cobalt spinel catalysts dispersed over various alumina supports (with varying alpha-, gamma-, delta- and theta-Al₂O₃ phase contents) were prepared and thoroughly characterized (XRF, XRD, μRS, SEM/TEM/EDX/SAED, TPR) and their reactivity was evaluated in low temperature N₂O decomposition as a probe reaction. The observed significant differences in catalytic activities were discussed in terms of the support's nature, active phase dispersion, nanocrystal morphology and the alumina support–Co₃O₄ interactions. The more reactive amorphous phase as well as the gamma-, delta- and theta-Al₂O₃ phases gives rise to high dispersion of the spinel nanocrystals (∼10 nm) which is, however, sacrificed by the formation of mixed Co_3−xAl_xO₄ spinels of much less activity. It was revealed that the best support for the deN₂O catalyst is an α-Al₂O₃ phase of micrometric grain size and the optimal size of the Co₃O₄ nanocrystals is in the range of 20–30 nm. This catalyst was also found to be more resistant to H₂O, NO and O₂ contaminants in comparison to the catalysts based on γ-Al₂O₃.