Revealing the strong interaction effect of MnOx nanoparticles and Nb2O5 supports with variable morphologies on catalytic propane oxidation

Abstract

Nb2O5 supports with pompom (Nb2O5-P), froth (Nb2O5-F) and layer-like (Nb2O5-L) morphologies were synthesized for the fabrication of supported MnOx catalysts. It has been demonstrated that the obtained catalysts exhibited variable catalytic activities for propane oxidation and notable diversity of physicochemical properties, which was closely related to the interface interaction between MnOx nanoparticles and Nb2O5 supports. Based on the comparison with a bulk catalyst (MnOx/Nb2O5-B), it was found that the morphology construction of Nb2O5 supports was favorable for boosting the catalytic activities of the catalysts, generally following an order of MnOx/Nb2O5-L > MnOx/Nb2O5-F > MnOx/Nb2O5-P > MnOx/Nb2O5-B. The optimum catalytic activity of MnOx/Nb2O5-L was attributed to its good surface dispersion, small dimension of MnOx nanoparticles and strong metal-support interaction, leading to significantly high low-temperature reducibility and lattice oxygen mobility, plentiful surface oxygen species and great proportion of Mn4+/Mn3+. However, MnOx/Nb2O5-L possessed inadequate thermal and catalytic stability with irreversible deactivation after long-term catalytic reactions. Characterization results of the deactivated catalyst revealed that the severe agglomeration and sintering of surface MnOx nanoparticles resulted in dramatically poor surface metal dispersion, low redox capacity and serious shortage of surface active oxygen species, which were recognized to be the predominant factors responsible for catalytic deactivation.