Selective oxidation of styrene to benzaldehyde with Cr-WO₃ ultrafine nanowires

The oxidation of styrene to benzaldehyde has advantages of mild conditions and no chlorine impurities in the product, and the design of highly active catalyst is the core. As a solid acid catalyst, WO₃ has excellent performance in thermal oxidation reaction, but its activity is limited by small specific surface area and high B acid content. In this work, the Cr^{3 +} cation was introduced as a modifier during the preparation of WO₃. The adsorption of Cr^{3 +} cations on non-(001) crystal plane realized the transformation of WO₃ from nanorods to ultrafine nanowires (UNWs), and the specific surface area of obtained Cr-WO₃ UNWs increased to 297 m²/g. In addition, Cr^{3 +} cation could dope into the lattice of WO₃ and slow down its crystallization, both of which effectively enriched the surface oxygen vacancies (L acid sites) of WO₃. In the reaction of selective oxidation of styrene to benzaldehyde, Cr-WO₃ UNWs effectively increased the conversion of styrene and the selectivity of benzaldehyde from 19.0% and 49.6% of pure WO₃ nanorod to 72.0% and 84.6% respectively under the optimized condition of 70 ℃, r(n_H2O2/n_styrene)=2.0, 6 h and m=30 mg. The improvement of catalytic performance can be attributed to the following two reasons:(1) the large specific surface area can provide sufficient active site for reaction; (2) the L acid site can activate H₂O₂ into active W-OOH, and an increase in the concentration of L acid site is beneficial for the production of more active species.