The characterization of mesoporous Ti-MCM-41 prepared at ambient temperature, with Ti contents in the 0.15 - 2.00 wt% range, was carried out using XAFS, FT-IR and photoluminescence methods. For Ti contents up to 0.60 wt%, isolated tetrahedrally coordinated Ti-oxide species was found to be formed in the MCM-41 network structures, while at higher titanium contents, dimeric or oligomeric Ti-oxide species, with Ti (IV) in tetrahedral coordination, became overwhelming. It was found that only the highly dispersed isolated tetrahedrally coordinated Ti-oxide species act as active sites in the photocatalytic decomposition of NO into N-2 and O-2.