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^?, O^2?) based on O₂-TPD.