Highly efficient and magnetically recyclable Pd catalyst supported by iron-rich fly ash@fly ash-derived SiO₂ for...

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 k_obs-p-NP/C_M (L min^-1 g_M^-1, M = precious metals) values and ˜3800× increases in price-normalized k_obs-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.