Title:Kinetic Analysis of Solvent Effect in the Photocatalytic, Aerobic Oxidation
of Benzyl Alcohol over P25
Volume: 4
Author(s): Nosaibeh Nosrati-Ghods, Nicholas Stuart Featherstone and Eric van Steen*
Affiliation:
- Catalysis Institute, Department of Chemical Engineering, University of Cape Town, South Africa
Keywords:
Photo-oxidation, benzyl alcohol, benzaldehyde, TiO2-P25, solvent effects, deposits.
Abstract:
Background: Photocatalysis is of particular importance in the oxidation of alcohols to
aldehydes to increase the conversion of benzyl alcohol oxidation to benzaldehyde at high selectivity,
which could be useful for the pharmaceutical and perfumery industries.
Objective: The oxidation of benzyl alcohol over P25 was investigated in various solvents (water,
benzotrifluoride, toluene and acetonitrile).
Methods: The reaction was performed in an isothermal slurry batch reactor in the presence and absence
of UV-light. The products were analysed using GC-FID; the deposits formed on the catalyst
was analysed using TGA and FTIR.
Results: In the presence of light, the reaction was very selective for the formation of benzaldehyde
(e.g., 99% selectivity at 53% conversion using acetonitrile as a solvent), whereas, in the absence of
light, the formation of higher molecular weight products was observed (e.g., 22% selectivity at
1.7% conversion using acetonitrile as a solvent). It was observed that the activity in the absence of
oxygen was initially high, but it dropped rapidly from initially 0.4 to 0 mmol g-1 h-1 after 2-4 h (using
acetonitrile as a solvent). This was attributed to the activity of the few oxidized sites present on
P25.
Conclusion: Acetonitrile appears to be the most effective solvent, as it seems to interact least with
the catalytically active sites. The photocatalytic oxidation of benzyl alcohol over P25 does not only
yield products in the solution, but also deposits on the surface. The deposits can be removed in an
oxidative environment or an inert environment.