Observation of Sublattice Disordering of the Catalytic Sites in a Complex Mo-V-Nb-Te-O Oxidation Catalyst Using High Temperature STEM Imaging

A Mo-V-Nb-Te-O oxidation catalyst has been imaged using scanning transmission electron microscopy at 780 K, which is slightly above its operating temperature. We observe a sublattice disordering of the corner-sharing octahedra forming the catalytic sites containing V5+ while the edge-sharing pentagonal bipyramidal {Nb(Mo-5)} sublattice remains structurally more rigid and thereby maintains the overall structural integrity of the catalyst. Imaging the termination of the edges of the [001] basal zones at room temperature reveal a preference for presence of a closed network of secondary structural {Nb(Mo)(5)} units providing further evidence of the stability of this sublattice structure. We propose that sublattice disordering of catalytic sites enables structural flexibility to accommodate different oxidation states during multistep chemical reactions within a more rigid superstructure and presents a new paradigm for compositionally and structurally complex catalysts.