Four distinct crystalline Mo3VO x catalysts comprising the same structural units were tested for the selective oxidation of methacrolein (MCR). Crystalline orthorhombic Mo3VO x (Orth-MoVO), trigonal Mo3VO x (Tri-MoVO), and amorphous Mo3VO 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 Mo3VO 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 Mo3VO 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 Mo3VO 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.

The catalytic activity of an aluminum complex/silanol system was found to vary with the aluminum ligand as follows: β‐diketonate < β‐ketoester anion < ortho‐carbonylphenolate. Aluminum complexes with electron donating groups conjugated with a carbonyl group had higher catalytic activity. The catalyst activity correlated with the strength of interaction between the aluminum complex and the silanol; there were two such interaction mechanisms. Cyclohexene oxide was polymerized cationically by the activated proton of SiOH. The activated proton is considered to be similar to Brönsted acid on silica‐alumina catalyst; therefore, the catalyst would be a model of the silica‐alumina catalyst.