Heteropoly Compounds as Ammoxidation Catalysts

Abstract

This chapter gives an overview of the work carried out in our group on the application of various forms of heteropoly acids (HPAs) for ammoxidation of methylpyrazine (MP). It starts with a general description of HPAs, ammonium salts of HPA, and the metal substituted HPAs (combinedly called as heteropoly compounds, HPCs). The various methods adopted for the synthesis of these compounds have been described. The HPCs have also been dispersed on different supports, and the methodology of their preparation is presented. Different characterization techniques have been used to determine their physicochemical properties. The reactivity of the catalysts is evaluated for the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP). The enhanced thermal stability and activity of the supported systems compared with those of the bulk ones are highlighted. Two new methods – one for the preparation of catalysts by in situ synthesis of the ammonium salt of heteropoly acid on supports and the other for the determination of dispersion of HPC on the support by FTIR technique – developed in our laboratory are introduced. Finally, correlations drawn between the activity and selectivity with the physicochemical properties of HPCs are presented.