Synthesis and Investigation of ZrO2–SiO2 Oxide Alloyed with Sn(IV) Ions

Mixed ZrO 2 –SiO 2 –SnO 2 oxides are synthesized by sol-gel method with atomic ratios of the components Zr : Si : Sn = 1 : 2 : x , where x = 0.1–4.0. By using thermogravimetric and XRD analysis, it is shown that the specimens with x ≤ 2 are characterized by highly homogeneous distributions of Sn 4+ ( x = 4) cations. As their content increases further, we observe the formation of a separate phase of tin dioxide, which corresponds to the tetragonal crystal structure of the rutile type. It is shown that the introduction of tin ions into the ZrO 2 –SiO 2 matrix leads to an increase in the acidity of the obtained specimens. In particular, the maximal strength of the acid sites ( H 0 ) increases from – 11.35 for ZrSi 2 to – 14.52 for ZrSi 2 Sn 0.4 and ZrSi 2 Sn. In the XPS spectra, the high-energy shifts of Zr 3 d 5/2 and Sn 3 d 5/2 levels serve as an indication of the shift of electron density from zirconium and tin atoms to the atoms of silicon. We recorded the presence of octahedral and tetrahedral coordinated Sn 4+ cations on the surface of ZrSi 2 Sn x specimens, which can be referred to Brönsted and Lewis acid sites. The role of Brönsted sites can be played by bridging –OH groups on VIII Zr 4+ and IV Zr 4+ cations, while the role of Lewis sites can be played by the coordinate-wise unsaturated zirconium and tin cations.