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| 2. |
- Selling, Anna, et al.
(författare)
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Reduced molybdovanadophosphates
- 2002
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948. ; :3, s. 743-9
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium speciation in the aqueous H+/MoO42-/ HVO42-/HPO42-/e(-) system, 0.600 M Na(CI) medium at 25 degreesC, was characterised by potentiometric [H+] (glass electrode) and {epsilon(-)} (platinum electrode) titration techniques as fundamental tools, complemented by V-51(V) NMR (131.6 MHz) and V-IV ESR spectroscopy. The study has been focused on solutions with the Keggin ratio, (Mo + V)/P = 12:1 and Mo/V > 5, in the pH range 1.4-4,5, where anions having the formula [(HzMo12-x-yVxVyPO40)-V-V-P-IV]((3+x+2y-z)-) are predominant species. Added numbers of electrons per vanadium(V) (e(-)/V-V) have been kept less than one to exclude reduction of molybdenum(VI). Six reduced molybdovanadophosphate species have been identified. The [(MO11VPO40)-P-IV](5-) species [logbeta = 154.15 +/- 0.03 (3sigma)] and the mixed-valence species [(Mo10VVPO40)-V-V-P-IV](6-) (logbeta = 155.84 +/- 0.02) can both be monoprotonated, These species have pK(a) values of 0.93 and 3.68, respectively. A "fully" reduced Keggin species, [(H2Mo10V2PO40)-P-IV](5-) (logbeta = 171.27 +/- 0.06), and a lacunary [(H4Mo10VPO39)-P-IV](5-) species (logbeta = 142.0 +/- 0.2) were found as well. Except for the molybdovanadophosphate species, the only reduced species formed, in the present investigation, is the vanadyl ion, VO2+. logK(red) (2 H+ + VO2+ + e reversible arrow VO2+ + H2O) was deterinined to 17.15 +/- 0.01 (E-0 = 1014.5 +/- 0.6 mV).
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| 3. |
- Taube, Fabian, et al.
(författare)
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Characterisation of aqueous peroxomolybdate catalysts applicable to pulp bleaching
- 2002
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 1364-5447. ; , s. 1002-1008
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium speciation in the system pH++qMoO42–+rH2O2+sSO42– (H+)p(MoO42–)q(H2O2)r(SO42–)s in 0.300 M Na2(SO4) medium at 25 °C has been determined from potentiometric titration data in the ranges 2.0 pH 5.5, 5.00 [Mo]tot/mM 80.00, 0 [H2O2]tot/mM 245 and 273.07 [SO42–]tot/mM 320.20. Species with the following compositions were found: MoX– (1,1,1,0), MoX (2,1,1,0), MoX2– (1,1,2,0), MoX2 (2,1,2,0), MoX2S2– (2,1,2,1), Mo2X42– (2,2,4,0), Mo7X6– (8,7,1,0), Mo7X5– (9,7,1,0), Mo7X4– (10,7,1,0) and Mo7X3– (11,7,1,0). The numbers in parentheses refer to the values of p, q, r and s in the formula above. The numbers and charges of molybdenum (Mo), peroxide (X) and sulfate (S) in each species are given in the abbreviated formula MoqXrSs(2q+ 2s–p)–. The following formation constants with 3 were obtained; log1,1,1,0= 8.53 ± 0.03, log2,1,1,0= 11.22 ± 0.04 (pKa= 2.69), log1,1,2,0= 11.61 ± 0.03, log2,1,2,0= 13.77 (± 0.06) (pKa= 2.16), log2,1,2,1= 14.50 ± 0.06, log2,2,4,0= 23.77 ± 0.11, log8,7,1,0= 56.71 ± 0.11, log9,7,1,0= 62.00 ± 0.05 (pKa= 5.29), log10,7,1,0= 65.74 ± 0.06 (pKa= 3.74), log11,7,1,0= 68.23 ± 0.08 (pKa= 2.49). Most complexes have been verified by 95Mo NMR, 17O NMR, and the novel MoX2S2– complex also by FTIR spectroscopy.
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| 4. |
- Taube, Fabian, et al.
(författare)
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Equilibria and dynamics of some aqueous peroxomolybdate catalysts: a 17O NMR spectroscopic study
- 2002
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 1364-5447. ; , s. 4451-6
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium speciation at 278 K and the dynamics in the systems pH++qMoO42–+rH2O2+sL (H+)p(MoO42–)q(H2O2)r Ls(L = SO42– or Cl–) in 0.3 M Na2(SO4) and 0.6 M Na(Cl) medium has been determined from 17O NMR integral and shift data in the range 0.7 pH 4.1 and at excess of peroxide ([H2O2]tot/[Mo]tot= 3). In 0.3 M Na2(SO4) medium species with the following compositions were found: MoX2–(1,1,2,0), MoX2(2,1,2,0), MoX2S2–(2,1,2,1), MoX2S–(3,1,2,1), Mo2X42–(2,2,4,0), Mo2X4–(3,2,4,0) and Mo2X62–(2,2,6,0), where (Mo) corresponds to MoO42–, (X) to O22– or HOO– and (S) to SO42–. In 0.6 M Na(Cl) medium the diperoxomolybdosulfate complex MoX2S– is replaced with a novel diperoxomolybdochloride complex MoX2Cl–(2,1,2,1), where (Cl) corresponds to Cl–. The numbers in parentheses refer to the values of p,q,r and s in the formula above. The stoichiometries of each complex are given by the abbreviated formula MoqXrSs(2q+ 2s–p)– and MoqXrCls(2q+s–p)–. The following formation constants with 3 were obtained with values for 0.6 M Na(Cl) in parenthesis: log 1,1,2,0= 11.61 (11.61); log 2,1,2,0= 13.70 ± 0.10, pKa= 2.09 (13.86 ± 0.10, pKa= 2.25); log 2,1,2,1= 14.57 ± 0.07 (13.87 ± 0.15 ); log 3,1,2,1= 15.27 ± 0.17, pKa= 0.70, log 2,2,4,0= 24.06 ± 0.05 (24.08 ± 0.04); log 3,2,4,0= 25.99 ± 0.18, pKa= 1.93 (26.23 ± 0.17, pKa= 2.15); log 2,2,6,0= 24.02 ± 0.15 (23.9 ± 0.3). The pKa value for HSO4– was determined to be 1.06 ± 0.11. At 278 K the MoX2 and Mo2X4 complexes are in chemical exchange and the rate of exchange increases upon protonation. At 312 K there is also measurable exchange between MoX2S and the MoX2 and Mo2X4 complexes. The dynamics in 0.6 M Na(Cl) medium seem to be very similar to those in the sulfate medium.
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