Oxidation of isobutane to methacrolein over Ga₂O₃/Bi₂Mo₃O₁₂ catalysts

Catalytic performance and the surface character of Ga₂O₃-supported Bi-Mo complex oxides were studied to obtain direct formation of methacrolein from isobutane. Bi₂Mo₃O₁₂ (• phase) and Bi₂MoO₆ (γ phase) showed higher catalytic activity than Bi2Mo200 ([~ phase) for isobutane partial oxidation. Supporting Ga₂O₃, which is an active catalyst for dehydrogenation of hydrocarbons, onto the oxides, enhanced the catalytic activity. The optimum amount of supported Ga₂O₃ on Bi₂Mo₃O₁₂ was ∼ 3 wt % for methacrolein formation. In the presence of oxygen, a remarkable amount of hydrogen over Ga₂O₃ during the isobutane oxidation but no hydrogen was formed over Ga₂O₃/Bi₂Mo₃O ₁₂. It is confirmed from TPR that Ga₂O₃ and Bi₂Mo₃O₁₂ were not reduced until 550°C but the reduction of Ga₂O₃/Bi₂Mo₃O ₁₂ started at 350°-380°C. The on-set temperature in TPR of the Bi-Mo complex oxides decreased to 350°-380°C from 500°C by the supporting Ga₂O₃ onto the oxides, and the catalysts after TPR measurement are composed of BiO, Bi, MoO₂ in addition to Bi₂Mo₃O₁₂. These results suggest that the hydrogen spillover took place over supported catalyst. Ga₂O₃/Bi₂Mo₁₂O ₁₂ catalyst showed higher activity and high selectivity for methacrolein at 450°C. In the non-aerobic oxidation of isobutane over the Ga₂O₃/Bi₂Mo₃O ₁₂ catalyst, the formation rate of CO_x significantly reduced, and methacrolein and isobutene were selectively obtained when the reduction degree of the catalyst was < 0.3% at 450°C.