Vanadium Phosphate Catalysts

Phosph(on/in)ate-Bridged Vanadium(IV) Dimers: Synthesis and Characterization

“…Investigation into the solid-state structure of VOPO 4 reveals an infinite lattice of vanadia octahedrally coordinated to oxygen atoms and phosphate tetrahedra . The metal centers are in a mixture of V 4+ /V 5+ oxidations states . Although the structure of the species has been characterized and understood for some time, mechanistically, the processes through which catalysis and oxidations occur remain convoluted.…”

“…To study a representative motif of an extended solid on a structurally simpler level, we have adopted the method of “dimensional reduction,” first described by Long et al, − but employed earlier by solid-state chemists. − Using this method we represent the truncated structure and oxidative activity of layered vanadium phosphate catalysts with a series of dinuclear organophosphorus-bridged model molecules. These model complexes employ the use of the facially coordinating, O,O,O-binding monoanionic ligand, η 5 -cyclopentadienyltris(diethylphosphito-κ 1 P ) cobaltate(III), [CpP OEt Co] − , first reported by Klaui and co-workers. , Use of this ligand gives the complexes structural and electronic similarities to industrially used catalysts; the molecules contain octahedrally coordinated vanadium centers and tetrahedral phosph(on/in)ate moieties in addition to metal centers in the desired (+4) oxidation state. A related complex synthesized by Carrano and co-workers made use of the N,N,N-binding ligand hydrotris(pyrazolyl)borate ligand, Tp – , and that group has reported a series of such dimers with phosphates and phosphonates. − During our efforts to model this widely used catalyst, several novel octahedral vanadium(III/IV) complexes were synthesized and structurally characterized.…”

“…12 The metal centers are in a mixture of V 4+ /V 5+ oxidations states. 13 Although the structure of the species has been characterized and understood for some time, mechanistically, the processes through which catalysis and oxidations occur remain convoluted. To study a representative motif of an extended solid on a structurally simpler level, we have adopted the method of "dimensional reduction," first described by Long et al, 14−16 but employed earlier by solidstate chemists.…”

“…These model complexes employ the use of the facially coordinating, O,O,O-binding monoanionic ligand, η 5 -cyclopentadienyltris(diethylphosphitoκ 1 P) cobaltate(III), [CpP OEt Co] − , first reported by Klaui and co-workers. 20,21 Use of this ligand gives the complexes structural and electronic similarities to industrially used catalysts; 13 the molecules contain octahedrally coordinated vanadium centers and tetrahedral phosph(on/in)ate moieties in addition to metal centers in the desired (+4) oxidation state. A related complex synthesized by Carrano and co-workers made use of the N,N,N-binding ligand hydrotris(pyrazolyl)borate ligand, Tp − , 22 and that group has reported a series of such dimers with phosphates and phosphonates.…”

Relationship between bulk phase, near surface and outermost atomic layer of VPO catalysts and their catalytic performance in the oxidative dehydrogenation of ethane

“…One of the characteristics that differentiate VPO catalysts from other catalytic systems is their complex activation, as the surface shows highly dynamic behaviour. In fact the variations in conversion and selectivity to maleic anhydride can change remarkably by slightly modifying the feed composition, flow and/or the activation treatment [29,30,31]. Overall, this commercial process has evolved for the past 4 decades from the first patent published by researchers of Monsanto in 1974 [25] with yields to maleic anhydride not exceeding 30%, to current values higher than 65% claimed by researchers from Lonza [32].…”