Reducing–Anchoring Dual Functions of Ti2O3 to Form Highly Dispersed MoO2/Ti2O3 as an Acid Catalyst for the Friedel–Crafts Reaction

Abstract MoO2, which is a molybdenum suboxide composed of Mo4+ species, exhibits structural and electronic properties that differ markedly from those of MoO3 composed of Mo6+. Owing to these distinct characteristics, MoO2 is regarded as a promising functional material for catalytic and other applications. Hence, the synthesis of MoO2 with fine structures such as fine particles and thin layers is crucial for these applications. However, reduction of MoO3 with H2, the conventional synthesis method for MoO2, requires high temperatures of 450–550 °C, which inevitably causes the particle growth and decreases the specific surface area, resulting in degraded catalytic performance. This study developed a material design that utilizes Ti2O3, a titanium suboxide, as a support with intrinsic reducing capability toward MoO3. This approach enabled simultaneous reduction of MoO3 to MoO2 and anchoring of the resulting MoO2 on the Ti2O3 surface, thereby suppressing excessive particle growth. In situ XRD measurements demonstrated that MoO3 supported on Ti2O3 was reduced to MoO2 under an inert atmosphere at significantly lower temperatures than the reduction with H2, driven by the strong reducing function of Ti2O3. Furthermore, STEM–EDX analysis revealed that MoO2 was strongly anchored to Ti2O3 surface and formed a thin-layered structure, indicative of effective growth suppression. MoO2/Ti2O3 catalyst synthesized in this reducing–anchoring manner exhibited exceptionally high activity and recyclability in the Friedel–Crafts reaction of anisole with benzyl chloride, largely outperforming other typical solid acid catalysts.