Process for the treatment of a gas stream containing nitrogen oxides comprising the steps of: providing a gas stream comprising N 2 O and NO x; contacting the gas stream provided in step with a transition metal containing zeolitic material having a BEA-type framework structure for reacting the nitrogen oxides; wherein the zeolitic material is obtainable from an organotemplate-free synthetic process, wherein the zeolitic material comprises YO 2 and X 2 O 3 and is obtainable by a process comprising the steps of preparing a mixture comprising one or more sources for YO 2, one or more sources for X 2 O 3, and seed crystals comprising one or more zeolitic materials having a BEA-type framework structure; crystallizing the mixture obtained in step; and subjecting the zeolitic material having a BEA-type framework structure obtained in step to an ion-exchange procedure with one or more transition metals; wherein Y is a tetravalent element, and X is a trivalent element, and wherein the mixture provided in step and crystallized in step does not contain an organotemplate as structure-directing agent, wherein the zeolitic material obtained in step is ion-exchanged with H + and/or NH 4 + and calcined prior to ion-exchange in step; and wherein the X-ray diffraction pattern of the zeolitic material having a BEA-type framework structure comprises at least the following reflections: Intensity (%) Diffraction angle 2θ/° [Cu K(alpha 1)] [11 - 31] [21.07 - 21.27] 100 [22.12 - 22.32] [13 - 33] [25.01 - 25.21] [17 - 37] [25.53 - 25.73] [13 - 33] [26.78 - 26.98] [11 - 31] [28.39 - 28.59] [22 - 42] [29.24 - 29.44] [6 - 26] [30.00 - 30.20] [9 - 29] [32.86 - 33.26] [11 - 31] [42.90 - 43.30] wherein 100 % relates to the intensity of the maximum peak in the X-ray powder diffraction pattern, wherein the gas stream provided in step further comprises one or more reducing agents, wherein the one or more reducing agents comprise one or more hydrocarbons and do not comprise ammonia and urea. providing a gas stream comprising N 2 O and NO x; contacting the gas stream provided in step with a transition metal containing zeolitic material having a BEA-type framework structure for reacting the nitrogen oxides; wherein the zeolitic material is obtainable from an organotemplate-free synthetic process, wherein the zeolitic material comprises YO 2 and X 2 O 3 and is obtainable by a process comprising the steps of preparing a mixture comprising one or more sources for YO 2, one or more sources for X 2 O 3, and seed crystals comprising one or more zeolitic materials having a BEA-type framework structure; crystallizing the mixture obtained in step; and subjecting the zeolitic material having a BEA-type framework structure obtained in step to an ion-exchange procedure with one or more transition metals; wherein Y is a tetravalent element, and X is a trivalent element, and wherein the mixture provided in step and crystallized in step does not contain an organotemplate as structure-directing agent, wherein the zeolitic material obtained in step is ion-exchanged with H + and/or NH 4 + and calcined prior to ion-exchange in step; and wherein the X-ray diffraction pattern of the zeolitic material having a BEA-type framework structure comprises at least the following reflections: Intensity (%) Diffraction angle 2θ/° [Cu K(alpha 1)] [11 - 31] [21.07 - 21.27] 100 [22.12 - 22.32] [13 - 33] [25.01 - 25.21] [17 - 37] [25.53 - 25.73] [13 - 33] [26.78 - 26.98] [11 - 31] [28.39 - 28.59] [22 - 42] [29.24 - 29.44] [6 - 26] [30.00 - 30.20] [9 - 29] [32.86 - 33.26] [11 - 31] [42.90 - 43.30] wherein 100 % relates to the intensity of the maximum peak in the X-ray powder diffraction pattern, wherein the gas stream provided in step further comprises one or more reducing agents, wherein the one or more reducing agents comprise one or more hydrocarbons and do not comprise ammonia and urea. preparing a mixture comprising one or more sources for YO 2, one or more sources for X 2 O 3, and seed crystals comprising one or more zeolitic materials having a BEA-type framework structure; crystallizing the mixture obtained in step; and subjecting the zeolitic material having a BEA-type framework structure obtained in step to an ion-exchange procedure with one or more transition metals;