Lilong Zhou, Lei Wang, Hui Wang, Yunli Cao, Ruiyi Yan and Suojiang Zhang
The Cu2+ or Fe3+ substituted Cs2HPMo12O40 was synthesized to study the effect of transitional metal cations on selective catalytic oxidation of methacrolein by polyoxometalates. Adding of Cu2+ could reduce acidity and enhance oxidizing ability of the catalyst. The catalytic experiments showed that the addition small amount of Cu2+ to the catalyst could increase the conversion of methacrolein from 65% to 96% and the selectivity to methacrylic acid to 55%, at 300-340°C. It is found adding of Cu2+ could promote the reduction process of catalysts should be the main reason of the performance enhancement. Adding of Fe3+ to the catalyst could induce some new weak acidic sites due to the formation of iron aqua complexes. Whereas, Fe3+ had no significant effect on redox ability of the catalyst. The conversion of methacrolein could reach 96% with the existence of Fe3+. However, the addition of Fe3+ had no significant effect on selectivity to methacrylic acid.