Effect of vanadium on the selective oxidation of methacrolein to methacrylic acid over Cs_2H_(x+1)PMo_(12)__xV_xO_(40) Catalysts

摘要

Cs_2Hx+1PMo_(12-x)V_xO_(40) (x = 0 3) catalysts were prepared, characterized and tested for the selective oxidation of methacrolein to methacrylic acid to investigate the effect of vanadium on the physi-cochemical properties and catalytic behavior of the catalysts. The catalysts before and after reaction were characterized by N, physisorption, FT-IR, XRD, XPS, NH_3-TPD and H_2-TPR. The characterization results show that the structural symmetry of the catalysts with vanadium substituting for Mo is reduced, and the acidity and the redox abilities of the catalysts vary with the amounts of vanadium. For the oxidation of methacrolein to methacrylic acid, the optimized acidity is beneficial for the selectivity to methacrylic acid, and high surface area and reducibility of the V atoms can enhance the activity of the catalysts. The best catalytic performance is obtained on Cs_2H_2PMo_(11) VO_(40), and excessive amounts of vanadium (x = 2, 3) are detrimental to the activity and selectivity of the catalysts.