MnOx/SBA-15 catalysts with different manganese content were studied for the selective oxidation of toluene by oxygen under solvent-free conditions. The catalyst with a manganese content of 6 wt% shows high catalytic efficiency and benzoic acid selectivity, whereas the selectivity to benzaldehyde increases remarkably upon increasing manganese content to 17 wt%. Several techniques such as N-2-physisorption, X-ray diffraction, diffuse reflectance spectra, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy were used to characterize the catalysts. Toluene adsorption investigations over catalysts reveal that the 6 wt% MnOx/SBA-15 catalyst has better adsorption capacity. The structure-performance correlation suggests that the well-isolated manganese species with tetrahedral coordination and greater numbers of adsorption sites account for the efficient oxidation of toluene to benzoic acid, whereas the MnOx clusters are less active and depress further oxidation to benzaldehyde and benzoic acid formation. Additionally, reaction temperature, time, catalyst mass, pressure and catalyst reusability were investigated over 6 wt% MnOx/SBA-15. A calculated turnover frequency of 532 h(-1) was obtained in 1 h at 180 degrees C. Rate-retarding effects of inhibitors and oxidation took place even without catalyst at 300 degrees C, respectively, indicate a radical chain mechanism. (C) 2015 Elsevier B.V. All rights reserved.