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

Abstract

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 (K_Pd–Ag ≈ 51 100 min⁻¹ mmol⁻¹) compared to the reported bimetallic Pd–Ag nanocatalysts.