Cyclic voltammetric evidence of facilitation of the reduction of nitrite by the presence of molybdenum in Fe- or Cu-substituted heteropolytungstates

Fe- or Cu-containing Dawson-type tungtodiphosphates substituted by two, fou r or five Mo atoms are studied by cyclic voltammetry at pH 3 and 5. Their c atalytic activities towards the reduction of nitrite are established and co mpared with those of the corresponding Fe- or Cu-substituted fully tungstic Dawson heteropolyanions. Whatever the pH, the presence of Mo atoms in the catalysts is found to be beneficial as concerns the current intensity or th e potential location of the catalytic wave. Specifically, it is found that the first step with Fe derivatives is the formation of a nitrosyl complex w hich is further reduced at the potential of a subsequent wave of the hetero polyanion. In the case of Cu- and Mo-substituted compounds, the two heteroa toms are found to exert their beneficial influence in concert. (C) 2001 Els evier Science B.V. All rights reserved.