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-A(3+) sites (1.1 x 10(16) m(-2)) that appear to be associated mainly with the crystallite edges, and a large majority (>98%) of diamagnetically-coupled Ti-A-B(3+) 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 Tig(oct)(4+) sites become reduced to paramagnetic Ti-A(3+) at 78 K, and mainly to spin-pairs at 300 K, with implications for their subsequent reactivity with oxidising gases. (C) 2018 Elsevier Inc. All rights reserved.