Jack W. Johnson

On the topotactic dehydration of VOHPO4 · 0.5 H2O into vanadyl pyrophosphate

Abstract The thermal analysis (DTA, TGA) of the dehydration under inert atmosphere of the vanadyl hydrogen phosphate hydrate VOHPO 4 · 0.5 H 2 O recently studied, together with the characterization of both starting and final compounds (XRD, ir, and uv-visible spectroscopies) show that pseudomorphic vanadyl pyrophosphate is obtained in these conditions. This form γ-(VO) 2 P 2 O 7 is the active and selective catalyst in butane oxidation to maleic anhydride whereas β-(VO) 2 P 2 O 7 is selective in butene oxidation only. Pseudomorphic relations between VOHPO 4 · 0.5 H 2 O and γ-(VO) 2 P 2 O 7 are evidenced by the comparison of XRD patterns, SEM and TEM experiments, and justified with the help of both structures. The low values of the activation energies calculated from kinetic data, E 1 = 21.4 and E 2 = 24.7 kcal · mole −1 show that the dehydration of the hydrate and the formation of γ are topotactic, this hypothesis is confirmed and the mechanism stated precisely in view of the preceding results.

Ion Exchange of the Layered Perovskite KCa2Nb3O10 by Protons.

Abstract The alkali cations in the layered perovskites MCa 2 Nb 3 O 10 (M ≡ K, Rb, Cs) are exchanged by protons in aqueous acid in a topochemical reaction to give HCa 2 Nb 3 O 10 . The unit cell of HCa 2 Nb 3 O 10 , as determined from powder X-ray diffraction, is tetragonal with a = 3.851 A and c = 14.38 A and contains one formula unit. The anhydrous hydrogen compound hydrates to form a composition HCa 2 Nb 3 O 10 ·1.5H 2 O which is also tetragonal with a = 3.854 A and c = 16.23 A . The hydration-dehydration behavior at 24 °C as a function of the partial water pressure shows significant hysteresis as a result of the expansion and contraction of the unit cell along the c axis.

Vanadyl hydrogenphosphate hydrates: VO(HPO4) · 4H2O and VO(HPO4) · 0.5H2O

Abstract Two vanadyl(IV) monohydrogenphosphate hydrates have been crystallized from aqueous media and their structures determined by single-crystal X-ray diffraction. The first, a tetrahydrate, VO(HPO4) · 4H2O, is triclinic, P 1 , with a = 6.379(2), b = 8.921(2), c = 13.462(3) A, α = 79.95(2), β = 76.33(3), γ = 71.03(3)°. Final residuals of R1 = 0.058 and R2 = 0.065 were obtained using 1250 unique data and 140 parameters. The second was found to be the hemihydrate, VO(HPO4) · 0.5H2O, with orthorhombic symmetry, Pmmn. Complete structure solution and refinement using data from a 2.7 × 105 μm3 crystal gave atomic parameters in close agreement with those recently reported in a parallel study (C. C. Torardi and J. C. Calabrese, Inorg. Chem. 23, 1308, 1984). Final residuals R1 = 0.041 and R2 = 0.042 were obtained on optimizing the 45 structural variables using 458 observed intensities. The structures of these two hydrates and that of the pyrophosphate, (VO)2P2O7, show a close correspondence. The degree of condensation of the vanadyl octahedra and phosphate tetrahedra, and the amount of water of crystallization in these materials are closely coupled and depend on the formation temperature.

Intercalation of the layered solid acid HCa2Nb3O10 by organic amines

Layered compounds of formula C/sub n/H/sub 2n+1/NH/sub 3/Ca/sub 2/Nb/sub 3/O/sub 10/ are formed by reaction of n-alkylamines with the solid acid HCa/sub 2/Nb/sub 3/O/sub 10/. Other organic bases such as pyridine can also be intercalated. The lattice constants of the new compounds have been determined by powder X-ray diffraction. The unit cells are tetragonal with a axes that are unchanged with variation of the intercalated amine. The c axes lengths (layer spacings) vary systematically with the hydrocarbon chain length of the alkylamine.

Winter diesel fuel production from a Fischer-Tropsch wax

A process for the production of a winter diesel fuel from wax containing hydrocarbons produced by the Fischer-Tropsch hydrocarbon synthesis process. A 300° F.+ Fischer-Tropsch fraction is upgraded first by hydroisomerization followed by catalytic dewaxing resulting in a diesel fuel suitable for use as a winter diesel fuel having excellent cold flow properties and reduced emissions.

Hydrothermal synthesis and single-crystal structural characterization of (VO)2[CH2(PO3)2] · 4H2O

Abstract The layered compound (VO) 2 [CH 2 (PO 3 ) 2 ] · 4H 2 O has been prepared by hydrothermal synthesis and characterized by single-crystal X-ray diffraction. The structure is orthorhombic, space group pbca with a = 12.805(4) A, b = 10.592(3) A, c = 15.037(5) A, Z = 8, D x = 2.462 g/cm 3 , R = 0.0372, and R w = 0.0500 for 2038 independent reflections. The structure is formed from layers of vanadium and oxygen atoms and methylenediphosphonate groups, with coordinated water molecules directed into the interlayer space, resulting in a layer repeat distance ( d 001 ) of 15.037(5) A. The layers contain two types of V 4+ O 6 octahedra connected through corners by [O 3 PCH 2 PO 3 ] 4- groups. V(1) is coordinated by one terminal oxygen atom and three oxygen atoms from water molecules, and chelated by one [O 3 PCH 2 PO 3 ] 4- group. V(2) is coordinated by one terminal oxygen atom, one water molecule, and two oxygen atoms from separate [O 3 PCH 2 PO 3 ] 4- groups, and chelated by one [O 3 PCH 2 PO 3 ] 4- group. The connectivity can be represented as VO 1 1 (H 2 O) 3 1 O 2 2 VO 1 1 (H 2 O) 1 1 O 4 2 (O 3 2 PCH 2 PO 3 2 ) . The structure illustrates the versatility of the [O 3 PCH 2 PO 3 ] 4- group as a connecting unit.

Redox transformations of simple vanadium phosphates: the synthesis of ε-VOPO4

Abstract A reproducible high yield hydrothermal synthesis of VPO 4 · H 2 O that minimizes the amount of organic species adsorbed on the solid particles has been developed. Oxidation of VPO 4 · H 2 O at ≤ 550 °C in oxygen has been shown to result in the formation of a new VOPO 4 phase that has been designated e-VOPO 4 . This new VOPO 4 phase is structurally distinct but related to the structures of β-VOPO 4 and VPO 4 · H 2 O. All three phases contain chains of corner-shared vanadium oxygen atom octahedra that are bridged by phosphate groups. The fully oxidized e-VOPO 4 is reduced to VPO 4 · H 2 O at 150 °C by a topotactic reaction with hydrogen in the presence of platinum (‘hydrogen spillover’).

Synthesis and crystal structures of two thallium vanadium phosphates: TIVO2(HPO4) and TI3V2O3(VO)(PO4)2(HPO4)

Abstract Two thallium vanadium phosphate compounds have been crystallized hydrothermally and their structures determined by single-crystal X-ray diffraction. The first, a hydrogen phosphate containing only vanadium(V), crystallizes at 450°C and is orthorhombic, space group Pbca, with a = 9.257(2) A, b = 17.518(4) A, and c = 6.810(2) A; V = 1104.4(5) A3; Z = 8; Dx = 4.610 g/cm3; R = 0.048; and Rw = 0.048 for 564 independent observed reflections with I ≥ 3σ(I). The structure can be described as chains of corner-sharing distorted square pyramids. Adjacent square pyramids are bridged by the phosphate groups. The chains are linked together by hydrogen bonds to form puckered layers stacked along the b axis. The thallium(I) atoms are approximately 7-coordinated by oxygen atoms in sites between the layers. The compound is isostructural with the MVO2(HPO4) (M = K, Rb, and NH4) compounds whose structures were recently determined by powder X-ray diffraction (1). The second compound, prepared at 200°C, has the composition Tl3V2O3(VO)(PO4)2(HPO4) and contains both V(V) and V(IV). The structure is orthorhombic, space group Pnma, with a = 7.160(2) A, b = 13.378(2) A, and c = 14.422(1)A; V = 1381.4(7) A3; Z = 4; Dx = 5.378 g/cm3; R = 0.041; and Rw = 0.054 for 1093 independent observed reflections with I ≥ 3σ(I). The structure contains vanadium atoms in two independent sites. The vanadium atom V2 is octahedrally coordinated by six oxygen atoms and forms a OVOVOchain of composition VO(PO4)2 along the crystallographic a direction. The second vanadium atom (V1) is coordinated by five oxygen atoms in a square pyramidal arrangement and is found as a dimeric unit with composition V2O3(HPO4). The two different units are joined to form the complete vanadium phosphate framework structure by sharing the oxygen atoms of one phosphate group. Bond valence calculations indicate that the vanadium atom in the chain is V4+ and that the dimer contains equal amounts of V4+ and V5+. The two thallium atoms occupy distorted 8-coordinate sites in the framework.

Ion exchange reactions of the layered solid acid HCa2Nb3O10 with alkali metal cations

Abstract Ion exchange reactions of the layered solid acid HCa2Nb3O10 with alkali metal cations have been investigated in aqueous solutions at temperatures between ambient and 100°C. The extent of exchange differs for the different alkali metal cations. The exchange reaction, in general, does not alter the stacking of adjacent oxide layers and the structures of the exchange products differ only slightly in their interlayer separations. The results obtained in aqueous solution are compared with previous measurements of the exchange of KCa2Nb3O10 in molten salts at higher temperatures (1).

Hydrothermal synthesis and single-crystal structural characterization of VO(VO3)6(VO(C10H8N2)2)2

Abstract VO(VO3)6(VO(C10H8N2)2)2 has been synthesized by the hydrothermal reaction of V2O3 with 2,2′-bipyridine. The compound is monoclinic, space group P2 1 n (No. 14), a = 7.579 (2) A, b = 26.713 (8) A, c = 12.776 (3) A, β = 94.97 (2)°, Z = 2. Its structure consists of (VO3)n chains of corner-sharing pentavalent vanadium tetrahedra joined by V4+ square pyramids, with octahedral VO(C10H8N2)2 groups arrayed on the periphery of the chains. The V4+ sites are isolated magnetically, with the compound exhibiting Curie-Weiss behavior in the temperature range 10–300 K. The calculated μeff is 1.68 μ B V 4+ , close to the spin-only value.