Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Electrical Engineering, Measurement and Control Technology
Abstract Trifluoromethanesulphonic acid monohydrate CF3SO3H.H2O and its aqueous solutions have been evaluated as an electrolyte for methanol electro-oxidation. The performances of conventional noble metal catalysts in the pure monohydrate are very poor compared with those in 3 M sulphuric acid. This is contrary to previously published literature data, and possible reasons for the discrepancy are given. In aqueous solutions of CF3SO3H at concentrations between 10 and 50%wt. considerably improved performance is obtained and at 60° C the activities of the catalysts are in most cases slightly higher than in 3 M H2SO4. In addition the poisoning effect of acid radicals is considerably less in CF3SO3H than in H2SO4 solutions. Above 60° C, however, the aqueous CF3SO3 anion decomposes to produce sulphur, which poisons the noble metal catalysts. Carbon-13 NMR studies of the CF3SO3H/H2O/CH3OH system were carried out at 20 and 37° C. From the results it was concluded that no significant ester formation occurred between CH3OH and CF3SO3H.H2O at these temperatures. Earlier published data on1H NMR studies of these solutions had indicated that 100% of the methanol was involved in ester formation with the acid. A critical analysis of this1H NMR work is given. Cyclic voltammetric characterization of catalysts in 10 and 25%wt. aqueous CF3SO3H solutions gave similar results to those in 3 M H2SO4; however, at concentrations of 50% wt. the acid decomposed at 0.0 V to produce a sulphur species that poisoned the catalyst. The conclusion of the work was that while aqueous CF3SO3H solutions produced promising catalyst performance up to 60° C the slight improvement in performance over 3 M H2SO4 would not offset the greater expense of the CF3SO3H. In addition, it was suspected that the long-term stability of the aqueous solutions even at 60° C might be poor.
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