Selective Oxidation of Methacrolein over Crystalline Mo<sub>3</sub>VO<i><sub>x</sub></i> Catalysts and Comparison of Their Catalytic Properties with Heteropoly Acid Catalysts
Satoshi Ishikawa, Nagisa Noda, Masaki Wada, Shota Tsurumi, Wataru Ueda
Abstract
Four distinct crystalline Mo3VOx catalysts comprising the same structural units were tested for the selective oxidation of methacrolein (MCR). Crystalline orthorhombic Mo3VOx (Orth-MoVO), trigonal Mo3VOx (Tri-MoVO), and amorphous Mo3VOx (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 Mo3VOx (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 Mo3VOx 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 Mo3VOx 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.