Heterogeneous photo-catalysis from the perspective of the adsorbed state. The photo-oxidation of propan-2-ol to propan-2-one on rutile titanium dioxide.

O 2 -titrations accompanying ESR, adsorption isotherm and TPD studies of well-crystallised powdered rutile provide insights into the nature of the reduced surface following adsorption of propan-2-ol at 300 K. Estimates have been made of the mean dimensions of the octa-decahedral micro-crystallites, and of the manner in which UV-A radiation penetrates into a randomised particle-bed. The reduced surface contains a small fractional coverage (0.003monolayer) of paramagnetic Ti 3+ A sites (1.1 × 10 16  m −2 ) that appear to be associated mainly with the crystallite edges, and a large majority (>98%) of diamagnetically-coupled Ti 3+ A-B spin-pairs arranged in the form of extended defects on the crystallite faces. UV-A is found to activate only a thin layer of particles at the bed exterior (0.83%) on which a large fraction (>30%) of the Ti 4+ oct sites become reduced to paramagnetic Ti 3+ A at 78 K, and mainly to spin-pairs at 300 K, with implications for their subsequent reactivity with oxidising gases. [ABSTRACT FROM AUTHOR]