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†
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 Co3−xAlxO4 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.