Supercritical Antisolvent Precipitation of TiO2 with Tailored Anatase/Rutile Composition for Applications in Redox Catalysis and Photocatalysis

TiO2 with tailored anatase/rutile composition has been prepared from the supercritical antisolvent (SAS) precipitation of a range of titanium alkoxides. The calcination of the SAS TiO2 was monitored by in situ powder X-ray diffraction to determine the optimal calcination conditions for the formation of a mixed anatse/rutile phase TiO2. The SAS precipitated material calcined at 450 °C produced a predominantly anatase support while calcination at 750 °C resulted in a 90 wt% anatase and 10 wt% rutile TiO2. 5 wt% AuPd was added to the SAS TiO2 using an impregnation technique, with exceptional dispersion of the metals being observed by transmission electron microscopy. Mean metal particle sizes were determined to be below 1 nm for both anatase and anatase/rutile SAS TiO2 materials. These catalysts were found to be highly active for the selective oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. In addition the anatase/rutile SAS TiO2 was found to have comparable activity to commercial anatase/rutile mixed phase TiO2 for the photocatalytic splitting of water for hydrogen production.