Microwave-Assisted Synthesis of Pt/SnO[sub.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[sub.2] catalysts using microwave radiation. Pt(IV) and Sn(IV) inorganic precursors (H[sub.2] PtCl[sub.6] and SnCl[sub.4] ) and ammonia were used, which allowed the controlled formation of platinum particles on the anisotropic SnO[sub.2] support. The synthesized Pt/SnO[sub.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[sub.2] samples. The Williamson-Hall diagram showed SnO[sub.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[sub.2] particles. XPS results indicated relatively low average oxidation states of platinum, close to Pt metal. [sup.119] Sn Mössbauer spectroscopy indicated electronic interactions between Pt and SnO[sub.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[sub.4] . The catalytic activity of the Pt/SnO[sub.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[sub.2] support is 5 mol% with an apparent rate constant k = 0.59 × 10[sup.–2] s[sup.–1] . The Pt/SnO[sub.2] sample showed exceptional reusability and retained an efficiency of 81.4% after ten cycles.