1984 Volume 57 Issue 6 Pages 1449-1453
12-Molybdophosphoric acid and its metal salts, supported on SiO2 (H3PA and MPA/SiO2), were found to exhibit significant activities for the catalytic reduction of nitrogen monoxide with hydrogen or ammonia, the latter reductant being more reactive. The activity orders of the catalysts were as follows, depending on the reductant: Cu2+>Ag+>Ni2+>Cs+\simeq Co2+\simeq H+ (hydrogen), Cu2+>Co2+>H+>Ag+>Ni2+>Cs+ (ammonia). It is of value to mention also that H3PA/SiO2 exhibited ten times many activity when ammonia was applied. The extent of the cation exchange (X) of CuXH3−2XPA/SiO2 influenced the catalytic activity differently, depending again on the reductant, although the maximum activity was obtained with both reductants when X was 1.1. Nitrogen monoxide was decomposed by a stoichiometric reaction with the reduced site on Cu1.1H0.8PA/SiO2, especially when the catalyst was reduced with hydrogen, although no oxygen was detected in the product, the initial rate being comparable to that of the reduction with hydrogen. The following rate-equations were obtained with the respective reductants on Cu1.1H0.8PA/SiO2 at 300 °C over the partial pressure range of NO (3.0–10.1 kPa) and reductants (3.0–35.5 kPa): V=kH2PNO0.8PH20.04, V=kNH3PNO0.6PNH30.04–−0.7. The wide range in the magnitude of powers with respect to the ammonia partial pressure in the latter equation implies the strong adsorption of ammonia on the catalyst. These results suggest that the redox and Langmuir mechanisms are plausible for the reactions with hydrogen and ammonia respectively. An ESR study of the copper and molybdenum ions of the catalyst supports the above mechanisms.
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