Highly efficient and magnetically recyclable Pd catalyst supported by iron-rich fly ash@fly ash-derived SiO2 for reduction of p-nitrophenol

In this study, a magnetically recyclable Pd catalyst was developed by using the novel support of iron-rich coal fly ash/silica (IRFA@SiO2) for highly efficient reduction of p-nitrophenol (p-NP). IRFA microspheres were coated with amorphous SiO2 synthesized from non-magnetic coal fly ash (NMFA) and then loaded with Pd by impregnation method for the synthesis of Pd/IRFA@SiO2. Various surface analyses demonstrated that amorphous SiO2 was well deposited on the surface of IRFA, providing a unique three-dimensionally structured SiO2 layer to suppress aggregation of IRFA and enhance dispersion of Pd nanoparticles. Pd/IRFA@SiO2 exhibited a significantly enhanced p-NP reduction than those of Pd/IRFA, Pd/Al2O3, and Pd/SiO2. Compared to other Pd- and metal-loaded catalysts, Pd/IRFA@SiO2 showed ˜4000× enhancements in kobs-p-NP/CM (L min-1 gM-1, M = precious metals) values and ˜3800× increases in price-normalized kobs-p-NP values, indicating that Pd/IRFA@SiO2 is a highly efficient and cost-effective alternative catalyst. The catalyst was successfully recycled five times without significant leaching of Pd, Si, and heavy metals because of the magnetic property of Pd/IRFA@SiO2. The experimental results suggest the applicability of the surface-modified IRFA support for the development of novel magnetically recoverable catalysts without severe toxicity problems.