Sulphuric acid and Pt treatment of the photocatalytically active titanium dioxide

The study focuses on preparation, surface sites characterization and catalytic activity testing of pure (TiO2), sulfated (TiO2-S), loaded with 1 wt% Pt (TiO2-Pt) and platinized/sulfated (TiO2-Pt-S) high surface area anatase TiO2 (100% anatase, 340 m2/g). Sulfation was performed in 4 M H2SO4 solution and was not followed by a high temperature calcination. TEM images reveal the formation of a 3 Å amorphous layer over TiO2 and TiO2-Pt surface after their sulfation. Infrared spectrum of TiO2-S contains additional absorption bands at 1235, 1333 and 1378 cm−1 that are assigned to SO stretch and distorted adsorbed SO42− vibrations. Low temperature CO adsorption and organic species adsorption from heptane solutions was performed for characterization of surface sites. TiO2-S showed 3–5 cm−1 shift of adsorbed CO absorption band compared to initial TiO2. The quantity of adsorbed CO increased by a factor of 1.5 for TiO2-S indicating the increase of the quantity of surface Lewis sites. Sulfation also resulted in disappearance of OH groups having absorption band at 3690 cm−1 that was attributed to substitution by monodentate and bidentate sulfates. Four bases and two acids with different pK were used as probes in solution titration revealing that the quantity of different acid sites in TiO2-S increases 1.07–2.17 times. Unexpectedly the quantity of acid and base sites in TiO2-Pt-S decreases relatively to other catalysts studied.Catalytic activity of the samples in acetone deep photooxidation was measured as a function of acetone vapor concentration in a flow-circulating reactor. All dependences are well described by the one site Langmuir–Hinshelwood kinetic model. The maximum oxidation rate was similar for all samples and was observed at acetone concentration above 1500 ppm. However, in the range of low acetone concentration the activity of TiO2-Pt-S was about triple of pure TiO2 activity. The high activity of sulfated/platinized and sulfated TiO2 is due to the much increased acetone adsorption constant.