Abstractdtalytic reduction of perchlorate in tha presence of molybdenum(V1) in 1 M acid solution depends not only on the concentration of perchlorate but also on the nature and the concentration of other anions present. The anionic species effect is attributed to the competitive ion pair formation with molybdenum. The estimated ion formation constants with perchlorate, bisulfate and trifluoromethanesulfonic acids are in the ratio of 2.9: 1.9: 1, respectively. The catalytic behavior of molybdenum(W) in the electrochemical reduction of perchlorate, chlorate and nitrate has been extensively studied by numerous investigators[ I-93. Several hypotheses have been proposed involving metastable molybdenum(W) or other transient species capable of reducing the perchlorate ion and in the process being reoxidized back to molybdenum(V) and recycled.
Theaagnitude of the catalytic reduction current for perchlorate to a great extent depends not only on the concentration of perchlorate and molybdate but also on pH, the nature of supporting electrolyte and, in particular, on the nature of the anion present in the supporting electrolyte. Thus, the previously reported data, as well as our results, suggest that the cationic molybdenum(V1) or molybdenum(V) species are essential for the catalytic process to be initiated and, furthermore, that it is essential to exclude the ligands which are able to stabilize the lower states of molybdenum and are able to compete for the cationic molybdenum species.
This investigation deals with the effect of the solution conditions on the electrochemical reduction of perchlorate in the presence of molybdenum(V1) and explores the possibility of the ion pair formation with the positively charged molybdenum species with the anions present in supporting electrolyte.
EXPERIMENTAL
Apparatus
The electrochemistry system Model 170 from Princeton Applied Research Corporation was used for the electrochemical studies employing a three electrode configuration; dropping mercury, dme, as a working electrode, a saturated calomel, see, as a reference, and a platinum foil as an auxiliary electrode, respectively. The temperature of a polarographic cell was thermostatted at 22"C, close to room temperature.