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(Redirected from Vanadium phosphate) Group of vanadium compounds used as oxidation catalysts

Vanadium phosphates
Identifiers
CAS Number	(anhydrous): 12359-27-2 (dihydrate): 12293-87-7
3D model (JSmol)	(anhydrous): Interactive image (dihydrate): Interactive image
ChemSpider	(anhydrous): 65999272 (dihydrate): 67027654
InChI (anhydrous): InChI=1S/H3O4P.O.V/c1-5(2,3)4;;/h(H3,1,2,3,4);;/q;;+3/p-3Key: MEVGAPWXIYXSPM-UHFFFAOYSA-K (dihydrate): InChI=1S/H3O4P.2H2O.O.V/c1-5(2,3)4;;;;/h(H3,1,2,3,4);2*1H2;;/q;;;;+3/p-3Key: IZKARBHCKXOZGC-UHFFFAOYSA-K
SMILES (anhydrous): P(=O)().O= (dihydrate): O.O.P(=O)().O=
Properties
Chemical formula	H₄O₇PV (dihydrate)
Molar mass	197.94 (dihydrate)
Appearance	yellow solid (dihydrate)
Solubility in water	insoluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

Chemical compound

Vanadium phosphates are inorganic compounds with the formula VO_xPO₄ as well related hydrates with the formula VO_xPO₄(H₂O)_n. Some of these compounds are used commercially as catalysts for oxidation reactions.

Vanadium(V) phosphates

A common vanadium phosphate is VOPO₄•2H₂O.

Seven polymorphs are known for anhydrous VOPO₄, denoted α_I, α_II, β, γ, δ, ω, and ε. These materials are composed of the vanadyl group (VO) and phosphate (PO₄). They are yellow, diamagnetic solids, although when contaminated with vanadium(IV) derivatives, samples exhibit EPR signals and have bluish cast. For these materials, vanadyl refers to both vanadium(V) oxo and vanadium(IV) oxo centers, although conventionally vanadyl is reserved for derivatives of VO.

Preparation, reactions, and applications of VOPO₄•2H₂O

Heating a suspension of vanadium pentoxide and phosphoric acid gives VOPO₄•2H₂O, isolated as a bright yellow solid. According to X-ray crystallography, the V(V) centers are octahedral, with long, weak bonds to aquo ligands.

Reduction of this compound with alcohols gives the vanadium(IV) phosphates.

These compounds are catalysts for the oxidation of butane to maleic anhydride. A key step in the activation of these catalysts is the conversion of VO(HPO₄)•0.5H₂O to the pyrophosphate (VO)₂(P₂O₇). This material (CAS#58834-75-6) is called vanadyl pyrophosphate as well as vanadium oxide pyrophosphate.

Vanadium(IV) phosphates

Several vanadium(IV) phosphates are known. These materials are typically blue. In these species, the phosphate anion is singly or doubly protonated. Examples include the hydrogenphosphates, VOHPO₄4H₂O and VO(HPO₄)0.5H₂O, as well as the dihydrogen phosphate VO(H₂PO₄)₂.

Portion of the crystal structure of VO(HPO₄)0.5H₂O. The vanadium is octahedrally coordinated and phosphorus is tetrahedral. Water is a bridging ligand. Color code: red = O; gray = V, H; ochre = P.

Vanadium(III) phosphates

Vanadium(III) phosphates lacking the oxo ligand have the formula VPO₄•H₂O and VPO₄•2H₂O. The monohydrate is isostructural with MgSO₄•H₂O It adopts the structure of the corresponding hydrated aluminium phosphate. Oxidation of VPO₄•H₂O yields the two-electron electroactive material ε-VOPO₄

Notes

The α_I and α_II polymorphs are sometimes called α₁ and α₂ instead.

References

Gautier, Romain; Gautier, Régis; Hernandez, Olivier; Audebrand, Nathalie; Bataille, Thierry; Roiland, Claire; Elkaïm, Erik; Pollès, Laurent Le; Furet, Eric; Fur, Eric Le (2013-05-15). "DFT-assisted structure determination of α₁- and α₂-VOPO₄: new insights into the understanding of the catalytic performances of vanadium phosphates". Dalton Transactions. 42 (22): 8124–8131. doi:10.1039/C3DT50217A. ISSN 1477-9234. PMID 23584576.
"New Contributions to the Structural Chemistry of Vanadyl Orthophosphate VOPO₄". edoc.mpg.de. Retrieved 2019-09-13.
Girgsdies, Frank; Schneider, Matthias; Brückner, Angelika; Ressler, Thorsten; Schlögl, Robert (2009-07-01). "The crystal structure of δ-VOPO₄ and its relationship to ω-VOPO₄". Solid State Sciences. 11 (7): 1258–1264. Bibcode:2009SSSci..11.1258G. doi:10.1016/j.solidstatesciences.2009.03.017. hdl:11858/00-001M-0000-0010-FAAA-9. ISSN 1293-2558.
Brody, John F.; Johnson, Jack W.; Vaughey, Jack (2007-01-05), Murphy, Donald W.; Interrante, Leonard V. (eds.), "Vanadyl Phosphates and Organylphosphonates", Inorganic Syntheses, John Wiley & Sons, Inc., pp. 241–248, doi:10.1002/9780470132616.ch45, ISBN 9780470132616
Tietze, Hr (1981). "The crystal and molecular structure of oxovanadium(V) orthophosphate dihydrate, VOPO₄(H₂O)₂". Australian Journal of Chemistry. 34 (10): 2035. doi:10.1071/CH9812035. ISSN 0004-9425.
Dummer, N.F.; Bartley, J.K.; Hutchings, G.J. (2011), "Vanadium Phosphate Materials as Selective Oxidation Catalysts", Advances in Catalysis, vol. 54, Elsevier, pp. 189–247, doi:10.1016/b978-0-12-387772-7.00004-6, ISBN 9780123877727
Koo, Hyun-Joo; Whangbo, Myung-Hwan; VerNooy, Paul D.; Torardi, Charlie C.; Marshall, William J. (2002). "Flux Growth of Vanadyl Pyrophosphate, (VO)₂P₂O₇, and Spin Dimer Analysis of the Spin Exchange Interactions of (VO)₂P₂O₇ and Vanadyl Hydrogen Phosphate, VO(HPO₄)·0.5H₂O". Inorganic Chemistry. 41 (18): 4664–4672. doi:10.1021/ic020249c. ISSN 0020-1669. PMID 12206689.
Vaughey, J. T.; Harrison, William T. A.; Jacobson, Allan J.; Goshorn, David P.; Johnson, Jack W. (1994). "Synthesis, structure, and properties of two vanadium(III) phosphates: V(PO₄)•H₂O and V_1.23(PO₄)(OH)_0.69(H₂O)_0.31•0.33H₂O". Inorganic Chemistry. 33 (11): 2481–2487. doi:10.1021/ic00089a027. ISSN 0020-1669.
Song, Y; Zavalij, PY; Whittingham, MS (2005). "ε-VOPO4: electrochemical synthesis and enhanced cathode behavior". Journal of the Electrochemical Society. 152 (4): A721–A728. Bibcode:2005JElS..152A.721S. doi:10.1149/1.1862265.
Lim, S; Vaughey, J. T.; Harrison, W. T. A.; Dussack, L. L.; Jacobson, A. J.; Johnson, J. W. (1996). "Redox transformations of simple vanadium phosphates: the synthesis of ε-VOPO4". Solid State Ionics. 84 (3–4): 219–226. doi:10.1016/0167-2738(96)00007-0.