Selective Oxidation of Isobutane to Methacrylic Acid by Metal-Substituted Ammonium Salts of Molybdovanadophosphoric Acid

A series of ammonium salts of molybdovanadophosphoric acid with different metal substitution and x values (abbreviated as (NH4)(1.85)M-x, M=Cs, Cu and Fe) were synthesized to catalyze the partial oxidation of isobutane to methacrylic acid. By XRD, TG/DTG, XRF, FT-IR, Raman spectroscopy, H-2-TPR, NH3-TPD, it can be found that, compared to the un-doped (NH4)(1.85)H2.15PMo11VO40 catalyst, the specific surface area, amount of acid sites, and immigrating amount of V atom in Keggin unit into the secondary structure were strongly dependent on the substituted metal ions and their content. The optimum activity was obtained over (NH4)(1.85)Cs-0.5 catalyst, which could provide a larger surface area of 37.72 m(2) g(-1), a higher amount of acid sites (82.47 mu mol g(-1)), and more VO2+ species and V2O5 clusters from the immigration of V atom in Keggin structure. Furthermore, Cu-substituted catalyst accelerated the catalytic cycle of isobutane oxidation due to the higher electron-delivering efficiency, and the MAA desorption became faster and the catalysts exhibited the excellent selectivity to MAA.

Automated summary

The series of ammonium salts of molybdovanadophosphoric acid with different metal substitution and x values were synthesized for catalyzing the partial oxidation of isobutane to methacrylic acid. Among them, the (Cs-0.5) catalyst exhibited the best activity with larger surface area, more acid sites, and increased migration of V atom, leading to improved selectivity to methacrylic acid.