Selective oxidation of cyclohexene to adipic acid over silver supported tungsten oxide nanostructured catalysts

Abstract

We have developed a new synthesis strategy to prepare ∼5 nm metallic silver nanoparticles (AgNPs) supported on tungsten oxide (WO₃) nanorods with diameters between 40 and 60 nm in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The catalyst was characterized by XRD, XPS, ICP-AES, FT-IR, Raman spectroscopy, EXAFS, SEM and TEM. The catalyst is very effective in liquid phase oxidation of cyclohexene to adipic acid with hydrogen peroxide as an oxidant. The synergy between the surface AgNPs and WO₃ nanorods plays the most vital role towards this very high catalytic activity. The reusability of the catalyst which is a prerequisite for practical applications was analysed and it was found that the catalyst exhibits no significant changes in its catalytic activity even after five cycles of reuse. A cyclohexene conversion of >99.9% with an adipic acid selectivity of ∼94% was achieved over ∼5 nm AgNPs supported on the WO₃ nanorod catalyst with a very high turnover frequency of ∼12 h⁻¹.