Activity and stability of TiO2 samples with different phase compositions in the decomposition of formaldehyde in SCW

TiO2 samples with different crystal sizes and compositions were synthesized using a sol-gel method at different calcination temperatures (350–900 °C). The activity and stability of TiO2 samples were determined by the gasification of formaldehyde in supercritical water (SCW) and by treatment in SCW. Increasing calcination temperature and SCW gasification (SCWG)/SCW treatment decreased the surface area of anatase TiO2 samples due to growing crystallite size via agglomeration and sintering. Among anatase TiO2 samples, the TiO2 calcinated at 450 °C was found as the most suitable material under SCW conditions. However, the surface area of rutile TiO2 slightly increased from 17.2 m2 g−1 to 19.8 m2 g−1 with the weakly crumbling of particles during SCWG. The highest hydrogen formation (63%) from formaldehyde in the SCW was obtained in the presence of anatase TiO2 calcined at 350 °C and rutile TiO2 calcined at 800 °C. CO2 formation in the presence of anatase TiO2 is higher than rutile TiO2 because of the presence of active lattice oxygen species (O−, O2−) based on O2-TPD.