How Do the Morphology and Crystal Facet of CeO2 Determine the Catalytic Activity toward NO Removal?

Abstract

Cerium oxide (CeO₂) exhibits application potential for the selective catalytic reduction of nitrogen oxides (NO_x) with NH₃ (NH₃-SCR). The crystal facets and morphology of CeO₂ have a vital impact on the catalytic performance of NH₃-SCR. However, the precise influence mechanisms on SCR activity remain elusive. In this work, CeO₂ is successfully synthesized with three distinct crystal facets and nine diverse morphologies. This investigation involves a comprehensive blend of theoretical analysis and experiments, to gain profound insights into the underlying mechanisms governing the SCR catalytic activity concerning morphology and crystal facets. By closely integrating density functional theory (DFT) calculations, Ab initio thermodynamic analysis, SCR catalytic activity experiments, and X-ray photoelectron spectroscopy experiments, it is discovered that the concentration of surface-active oxygen (O^*) plays a pivotal role in determining the catalytic activity of CeO₂ in SCR reactions, as opposed to factors like specific surface area or oxygen defect concentration. This experimental-theoretical joint study provides design principles of CeO₂ catalysts for NO removal.

Keywords: CeO2; DFT calculations; NO conversion; crystal facet; morphology.