P The invention relates to an ordered mesostructured or mesoporous material comprising a mineral phase within which particles of nanometric dimension at least partially crystalline are dispersed, which is characterized in that it also comprises at least one additive chosen from the group comprising alkalis, alkaline earths and manganese, the additive being present on the surface of the mineral phase and / or of the particles. This material is obtained by a process in which an ordered mesostructured or mesoporous material is formed comprising an inorganic phase within which particles of nanometric dimension at least partially crystalline are dispersed, then said material is impregnated with a solution or suspension comprising aforementioned additive, the solution or suspension having a pH of at most 8.5, and an additive concentration of at least 0.5M and finally the impregnated material is calcined. The material can be used as a catalyst, in particular for the treatment of exhaust gases from internal combustion engines or the treatment of gases for the reduction of emissions of nitrogen oxides. / P
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