Synthesizing alcohols and ketones by photoinduced catalytic partial oxidation of hydrocarbons in TiO2 film reactors prepared by three different methods

The partial oxidation of cyclohexane to cyclohexanol and cyclohexanone on UV-irradiated titanium dioxide films in the presence of molecular oxygen at low temperatures and atmospheric pressure was studied. Three different coating methodologies (dip coating using titanium isopropoxide and commercially available titanium dioxide particles, sol-gel process, and flame aerosol process) were used to deposit the titanium dioxide films, and their effectiveness in partial oxidation of cyclohexane was compared. Conversions of the cyclohexane in the gas-phase reactor averaged between 1.1 and 8.7% per pass (8-s contact time) for the different film reactors. The yield (formation of ketone and alcohol) exceeded 96% for all the film reactors. No detectable amount of carbon dioxide was generated. The selectivity for ketone formation ranged from 59 to 91%. The films produced by the flame aerosol method resulted in the highest yield per mass of catalyst used and showed no coking and deactivation for a total run time of approximately 10 h (2 cycles). The films were characterized by XRD, SEM, and TEM to establish the phase compositions, morphologies, and primary particle sizes, respectively. The flame aerosol coating resulted in the formation of high surface area aggregates consisting of nanometer-sized primary particles with high density (minimal internal porosity), whereas dip coating resulted in the formation of bulk crystallites that were more susceptible to coking and deactivation. The flame-aerosol-deposited titania particles had more surface sites per unit mass for photooxidation and minimal intraparticle diffusion limitations.