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Issue 6, 2002
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Characterisation of aqueous peroxomolybdate catalysts applicable to pulp bleaching

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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 + 2sp)−. The following formation constants with 3σ were obtained; log β1,1,1,0 = 8.53 ± 0.03, log β2,1,1,0 = 11.22 ± 0.04 (pKa = 2.69), log β1,1,2,0 = 11.61 ± 0.03, log β2,1,2,0 = 13.77 (± 0.06) (pKa = 2.16), log β2,1,2,1 = 14.50 ± 0.06, log β2,2,4,0 = 23.77 ± 0.11, log β8,7,1,0 = 56.71 ± 0.11, log β9,7,1,0 = 62.00 ± 0.05 (pKa = 5.29), log β10,7,1,0 = 65.74 ± 0.06 (pKa = 3.74), log β11,7,1,0 = 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.

Graphical abstract: Characterisation of aqueous peroxomolybdate catalysts applicable to pulp bleaching

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Article information


Submitted
03 Sep 2001
Accepted
28 Nov 2001
First published
05 Feb 2002

J. Chem. Soc., Dalton Trans., 2002, 1002-1008
Article type
Paper

Characterisation of aqueous peroxomolybdate catalysts applicable to pulp bleaching

F. Taube, M. Hashimoto, I. Andersson and L. Pettersson, J. Chem. Soc., Dalton Trans., 2002, 1002
DOI: 10.1039/B107936K

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