Fly ash supported Pd-Ag bimetallic nanoparticles exhibiting a synergistic catalytic effect for the reduction of nitrophenol

摘要

Coal fly ash (FA) supported Pd-Ag bimetallic nanoparticles (FA-Pd-Ag) were prepared by reducing Pd(II) and Ag(I) salts together onto the dispersed solid support in aqueous medium. Electron microscope analysis (FE-SEM, HRTEM) in combination with elemental mapping (EDS) suggests that the nanoparticles are well dispersed on fly ash with an average diameter of 6-8 nm. The powder XRD analysis indicates that alloying of the interface occurs between Pd and Ag nanoparticles in FA-Pd-Ag, while XPS reveals that charge transfer takes place between the Pd and Ag moieties that come into contact with each other. The FA-Pd-Ag in aqueous NaBH4 solution exhibits an efficient catalytic reduction of 4-nitrophenol into 4-aminophenol and follows pseudo-first-order reaction kinetics (k(Pd-Ag) = 0.7176 min(-1)). The higher rate constant for FA-Pd-Ag compared to that for their monometallic analogues (FA-Pd (k(Pd) = 0.5449 min(-1))) and (FA-Ag (k(Ag) = 0.5572 min(-1))) as well as their physical mixture ((FA-Pd + FA-Ag) (k(Pd+Ag) = 0.4075 min(-1))) suggests the synergistic catalytic effect of the bimetallic system. Moreover, the present bimetallic nanocatalyst exhibits the highest normalized rate constant (KPd-Ag approximate to 51 100 min(-1) mmol(-1)) compared to the reported bimetallic Pd-Ag nanocatalysts.