A series of nanosized N-containing TiO(2-)based materials with Anatase-type structure and synthesized by a microemulsion method were tested in the photocatalytic degradation of methylcyclohexene, a representative example of volatile organic compound (VOC) present in urban atmospheres. A combined diffuse reflectance infrared (DRIFTS) and X-ray absorption (XAS) spectroscopic study allows to analyze the nature and number of N-containing species and other defects (particularly oxygen vacancies) present in the solid catalysts. The structural characterization was used to interpret the UV-vis spectra of the solids and the resulting joint information allows to rationalize the photocatalytic activity differences observed through the samples under sunlight-type excitation. We founded that our samples contain substitutional and interstitial N-containing impurities and a significant number of oxygen vacancies. Photocatalytic activity is correlated with an optimum of oxygen vacancies, above and below which a decrease of the steady state reaction rate is observed. The physico-chemical bases of this behavior are discussed on the light of the above mentioned experimental results. (c) 2006 Elsevier B.V. All rights reserved.