Microwave-Assisted Synthesis of Pt/SnO(2) for the Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol

In this study, we present a new approach for the synthesis of Pt/SnO(2) catalysts using microwave radiation. Pt(IV) and Sn(IV) inorganic precursors (H(2)PtCl(6) and SnCl(4)) and ammonia were used, which allowed the controlled formation of platinum particles on the anisotropic SnO(2) support. The synthesized Pt/SnO(2) samples are mesoporous and exhibit a reversible physisorption isotherm of type IV. The XRD patterns confirmed the presence of platinum maxima in all Pt/SnO(2) samples. The Williamson-Hall diagram showed SnO(2) anisotropy with crystallite sizes of ~10 nm along the c-axis (< 00l >) and ~5 nm along the a-axis (< h00 >). SEM analysis revealed anisotropic, urchin-like SnO(2) particles. XPS results indicated relatively low average oxidation states of platinum, close to Pt metal. (119)Sn Mössbauer spectroscopy indicated electronic interactions between Pt and SnO(2) particles. The synthesized samples were used for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of excess NaBH(4). The catalytic activity of the Pt/SnO(2) samples for the reduction of 4-NP to 4-AP was optimized by varying the synthesis parameters and Pt loading. The optimal platinum loading for the reduction of 4-NP to 4-AP on the anisotropic SnO(2) support is 5 mol% with an apparent rate constant k = 0.59 × 10(–2) s(–1). The Pt/SnO(2) sample showed exceptional reusability and retained an efficiency of 81.4% after ten cycles.