Solid-State Dispersions of Platinum in the SnO₂ and Fe₂O₃ Nanomaterials

The dispersion of platinum (Pt) on metal oxide supports is important for catalytic and gas sensing applications. In this work, we used mechanochemical dispersion and compatible Fe(II) acetate, Sn(II) acetate and Pt(II) acetylacetonate powders to better disperse Pt in Fe₂O₃ and SnO₂. The dispersion of platinum in SnO₂ is significantly different from the dispersion of Pt over Fe₂O₃. Electron microscopy has shown that the elements Sn, O and Pt are homogeneously dispersed in α-SnO₂ (cassiterite), indicating the formation of a (Pt,Sn)O₂ solid solution. In contrast, platinum is dispersed in α-Fe₂O₃ (hematite) mainly in the form of isolated Pt nanoparticles despite the oxidative conditions during annealing. The size of the dispersed Pt nanoparticles over α-Fe₂O₃ can be controlled by changing the experimental conditions and is set to 2.2, 1.2 and 0.8 nm. The rather different Pt dispersion in α-SnO₂ and α-Fe₂O₃ is due to the fact that Pt⁴⁺ can be stabilized in the α-SnO₂ structure by replacing Sn⁴⁺ with Pt⁴⁺ in the crystal lattice, while the substitution of Fe³⁺ with Pt⁴⁺ is unfavorable and Pt⁴⁺ is mainly expelled from the lattice at the surface of α-Fe₂O₃ to form isolated platinum nanoparticles.