Selective Oxidation of Methacrolein over Crystalline Mo3VOx Catalysts and Comparison of Their Catalytic Properties with Heteropoly Acid Catalysts

Four distinct crystalline Mo 3 VO x catalysts comprising the same structural units were tested for the selective oxidation of methacrolein (MCR). Crystalline orthorhombic Mo 3 VO x (Orth-MoVO), trigonal Mo 3 VO x (Tri-MoVO), and amorphous Mo 3 VO x (Amor-MoVO) having pentagonal, hexagonal, and heptagonal channels in the crystal structure showed far better catalytic activity and selectivity to methacrylic acid (MAA) than those of various Mo–V-based mixed oxide catalysts. Tetragonal Mo 3 VO x (Tet-MoVO) having pentagonal and hexagonal but no heptagonal channels in the crystal structure provided minor MCR oxidation activity, and the MAA selectivity was lower than that of the other crystalline Mo 3 VO x catalysts with heptagonal channels. In situ Fourier transform infrared (FT-IR) measurements revealed that Orth-MoVO and Tri-MoVO were active with respect to MCR, forming methacrylate as a reaction intermediate, while no infrared (IR) bands related to surface compounds were observed over Tet-MoVO after the MCR injection. Based on these results, we concluded that the crystal structure of crystalline Mo 3 VO x catalysts significantly affects the catalytic MCR oxidation activity. Orth-MoVO catalyzed the MCR oxidation at low reaction temperatures (<240 °C), where the conventional catalyst used for the industrial MCR oxidation process, a heteropoly acid (HPA)-based catalyst, displayed poor catalytic activity.