LIMITING QUANTUM YIELD MEASUREMENTS FOR THE DISAPPEARANCE OF 1-PROPANOL AND PROPANAL - AN OXIDATIVE REACTION STUDY EMPLOYING A TIO2 BASED PHOTOREACTOR

Relative initial quantum yields (Phi(0 dis)' for the disappearance of 1-propanol and propanal were estimated based on total light intensity entering the reaction vessels. Two types of photocatalytic reactor geo metries were compared, a commercial prototype flow reactor with immobi lized TiO2, and a conventional reactor with TiO, dispersion. A maximum relative quantum yield, Phi(lim)' approximate to 1, was extrapolated for pure propanol and propanal in both geometries. The high quantum yi elds were attributed to efficient competition of substrate oxidation w ith electron-hole recombination, at high surface coverage. Propanal wa s identified as the primary intermediate generated from 1-propanol in both reactor systems, but yields of propanal were systematically 10 ti mes lower than l-propanol loss, indicating that there was an effective pathway for propanal oxidation on the surface prior to desorption. Th e inhibition of 1-propanol reaction caused by accumulation of product arises because both reactant and product compete for active sites on t he photocatalyst surface. These propositions were confirmed by introdu cing propanal into the feed. The relative quantum yields converge to u nity for pure substrates, suggesting that they are true yields. That i s to say, absorption by TiO, of light entering the reactor is efficien t in these geometries.