Ag and WOx Nanoparticles Embedded in Mesoporous SiO₂ for Cyclohexane Oxidation

A facile synthesis strategy has been undertaken to stabilize Ag nanoparticle inside the channels of mesoporous silica network. The resulting AgWS material exhibited highly ordered hexagonal pores in a 2D array with long 1D channels of p6 mm plane group with the relatively high surface area. Finely dispersed icosahedral Ag nanoparticles with WO3 nanoparticles of 5–10 nm diameter have been spotted over the catalyst. The as-prepared material shows promotional activity for the single-step conversion of cyclohexane to adipic acid (aa). DFT calculations suggested the reduction of activation energy to 8.5 eV (188 kcal/mol) from 11.36 eV (262 kcal/mol) for the W-complex, which is further reduced to 1.96 eV (45 kcal/mol) for the Ag–W complex. Thus, the promotional effects of Ag with the dual Lewis and Brønsted acidity of W-SBA-15 material endowed more efficiently facilitate the selective oxidation of cyclohexane to aa. Under optimized conditions using H2O2, ≥ 99% selectivity of adipic acid and 89.6% conversion at 90 °C in 16 h was observed.