Antimony doping reactions

Keggin-type phosphomolybdates (POM s) were tested as catalysts for the selective oxidation of isobutane to methacrylic acid. Doping the POM with antimony improves the catalytic performance especially at isobutane-lean conditions, since a redox reaction between Sb " " and Mo leads to the development of a reduced POM which is stable even in an oxidizing environment, and which is more selective to methacrylic acid. Another important factor to control the reactivity is the pH of precipitation of the POM. When the preparation of the catalyst is carried out via the formation of a lacunary precursor, the time necessary to reach steady catalytic performance ( equilibration time ) is considerably less than that for POM s prepared conventionally at strongly acid pH. An hypothesis about the nature of the active sites is formulated. 

In a previous work we found that the addition of small amounts of Sb3+ to the POM-based catalyst makes possible the occurrance of a redox reaction between Mo in the primary POM structure and antimony, with development of a reduced compound which is stable even under oxidizing conditions [19], The objective of the work reported here was twofold 1) to evaluate the catalytic performance of this Sb-doped POM catalyst in the title reaction, and 2) to analyze the effect of the pH of precipitation of the POM on its chemical-physical features and catalytic performance, as a possible parameter to control the reactivity of these compounds. 

Bushby reported several aminium-based polymers (22). Polyamine 5a (Mw > 10, GPC) was prepared by Suzuki reaction based polymerization, and then p-doped with antimony pentachloride. The resultant polyaminiiun polymer 5b had radical concentration of 0.5 radical/imit and an average value of S 4 (22). The ferromagnetic coupling was rather weak, as expected for extended exchange pathway of m-phenylene with two jo-phenylene spacers (Fig. 3). 

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