Effect of surface acidity of cyano-bridged polynuclear metal complexes on the catalytic activity for the hydrolysis of organophosphates

Abstract

Heterogeneous catalysis of cyano-bridged polynuclear metal complexes, which were prepared by systematic replacement of C-bound metal ions (M^C) and/or N-bound metal ions (M^N) of Prussian blue ([M^N(H₂O)_x]_y[Fe^II/III(CN)₆]; M^N = Fe^III, Ga^III, Mn^II, Zn^II or Co^II: [Fe^II/III(H₂O)_x]_y[M^C(CN)₆]; M^C = Fe^II, Pt^IV, Co^III, Ir^III or Ru^II), was examined for the hydrolysis of p-nitrophenol phosphate (p-NPP) as a model compound of insecticides. The catalytic activity of the complexes was enhanced by employing metal ions in higher oxidation states at the C- and N-bound sites, although only N-bound metal ions act as active sites. The dependence of the initial reaction rates for the hydrolysis on the initial concentration of p-NPP suggested that the rate determining step is the adsorption of p-NPP onto catalyst surfaces. The surface acidity of each complex estimated by the heat of pyridine desorption is strongly correlated with catalytic activity.