Direct Imaging of Octahedral Distortion in a Complex Molybdenum Vanadium Mixed Oxide

Abstract

Complex Mo, V based mixed oxides that crystallize in the orthorhombic M1-type structure are promising candidates for the selective oxidation of small alkanes. The oxygen sub-lattice of such a complex oxide has been studied by annular bright field scanning transmission electron microscopy. The recorded micrographs directly display the local distortion in the metal oxygen octahedra. From the degree of distortion we are able to draw conclusions about the distribution of oxidation states in the cation columns at different sites. The results are supported by X-ray diffraction and electron paramagnetic resonance measurements that provide integral details about the crystal structure and spin coupling, respectively.

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

“…This postulate renders the precise structure determination of the oxide phase in question into a decisive [32][33][34][35][36][37][38][39] experiment. It is noted here that with the increasing precision of structured determination [40] not only intergrowth of minority phases that cannot be seen easily with diffraction methods but also local dynamics at interconnection sites of polyhedra supporting the notion of surface reconstruction in termination phases have been observed [41,42] experimentally.…”

Site specific and localized structural displacements in open structured multimetallic oxides

“…5,6 Among the huge variety of functional materials, high-performance catalysts, such as multimetallic molybdenum-and vanadium-based oxides, which can crystallize in an open crystal structure, are highly susceptible to geometric and compositional defects, such as different cation occupancies, polyhedral distortions or structural reconnectivities. 2,4,[7][8][9] Prominent oxides of this family have an orthorhombic unit cell (space group: Pba2) and crystallize in the so-called M1 structure. The unit cell of the M1 structure is composed of 44 metal atoms that are distributed over 13 crystallographic different metal sites (S).…”

“…[10][11][12] These channels can be partially occupied by cationic species of tellurium, antimony, vanadium or ammonium. 7,[10][11][12][13] Furthermore, complex molybdenum and vanadium mixed oxides represent non-stoichiometric compounds. Thus, in order to accomplish charge neutrality, the intrinsic oxidation states of molybdenum and vanadium within these materials depend on the metal and oxygen composition.…”

A zeolitic vanadotungstate family with structural diversity and ultrahigh porosity for catalysis

“…The typical materials are porous frameworks based on ring-shaped [P 8 W 48 O 184 ] unit 14,15 , [MnV 13 O 38 ] unit 16 , and pentagon [Mo 6 O 21 ] units 17 . However, the current materials suffer from problems that include poor structural diversity, unopened micropores 18 , and low surface area and porosity 18,19 . Therefore, new progresses in obtaining zeolitic materials with all-transition metal oxides that would increase the diversity of material design are strongly desired by material scientists.…”