A process for preparing a tin-containing zeolitic material having an MWW-type framework structure (Sn-MWW) comprising (i) providing a boron-containing zeolitic material having an MWW framework structure comprising SiO 2 and B 2 O 3 (B-MWW); (ii) deboronating the B-MWW by treating the B-MWW provided in (i) with a liquid solvent system having a pH in the range of from 5.5 to 8; (iii) incorporating Sn into the deboronated B-MWW obtained from (ii) by a process comprising (iii.1) preparing an aqueous synthesis mixture containing the deboronated B-MWW obtained from (ii), an MWW template compound, preferably selected from the group consisting of piperidine, hexamethylene imine, N,N,N,N',N',N'-hexamethyl-1,5-pentanediammonium ion, 1,4-bis(N-methylpyrrolidinium)butane, octyltrimethylammonium hydroxide, heptyltrimethylammonium hydroxide, hexyltrimethylammonium hydroxide, and a mixture of two or more thereof, and a tin source, wherein in the synthesis mixture, the molar ratio of Sn, calculated as SnO 2, relative to Si, calculated as SiO 2 and contained in the deboronated B-MWW, is at most 0.015: 1; (iii.2) hydrothermally synthesizing a tin-containing zeolitic material having an MWW-type framework structure from the synthesis mixture obtained from (iii.1) thereby obtaining a tin-containing zeolitic material having an MWW-type framework structure in its mother liquor; (iii.3) separating the tin-containing zeolitic material having an MWW-type framework structure obtained from (iii.2) from its mother liquor; (iv) treating the tin-containing zeolitic material having an MWW-type framework structure obtained from (iii) with an aqueous solution having a pH of at most 5 thereby obtaining the Sn-MWW having an Sn content of at most 2 weight-%, calculated as element and based on the weight of the Sn-MWW, and optionally separating the Sn-MWW from the aqueous solution. (i) providing a boron-containing zeolitic material having an MWW framework structure comprising SiO 2 and B 2 O 3 (B-MWW); (ii) deboronating the B-MWW by treating the B-MWW provided in (i) with a liquid solvent system having a pH in the range of from 5.5 to 8; (iii) incorporating Sn into the deboronated B-MWW obtained from (ii) by a process comprising (iii.1) preparing an aqueous synthesis mixture containing the deboronated B-MWW obtained from (ii), an MWW template compound, preferably selected from the group consisting of piperidine, hexamethylene imine, N,N,N,N',N',N'-hexamethyl-1,5-pentanediammonium ion, 1,4-bis(N-methylpyrrolidinium)butane, octyltrimethylammonium hydroxide, heptyltrimethylammonium hydroxide, hexyltrimethylammonium hydroxide, and a mixture of two or more thereof, and a tin source, wherein in the synthesis mixture, the molar ratio of Sn, calculated as SnO 2, relative to Si, calculated as SiO 2 and contained in the deboronated B-MWW, is at most 0.015: 1; (iii.2) hydrothermally synthesizing a tin-containing zeolitic material having an MWW-type framework structure from the synthesis mixture obtained from (iii.1) thereby obtaining a tin-containing zeolitic material having an MWW-type framework structure in its mother liquor; (iii.3) separating the tin-containing zeolitic material having an MWW-type framework structure obtained from (iii.2) from its mother liquor; (iii.1) preparing an aqueous synthesis mixture containing the deboronated B-MWW obtained from (ii), an MWW template compound, preferably selected from the group consisting of piperidine, hexamethylene imine, N,N,N,N',N',N'-hexamethyl-1,5-pentanediammonium ion, 1,4-bis(N-methylpyrrolidinium)butane, octyltrimethylammonium hydroxide, heptyltrimethylammonium hydroxide, hexyltrimethylammonium hydroxide, and a mixture of two or more thereof, and a tin source, wherein in the synthesis mixture, the molar ratio of Sn, calculated as SnO 2, relative to Si, calculated as SiO 2 and contained in the deboronated B-MWW, is at most 0.015: 1; (iii.2) hydrothermally synthesizing a tin-containing zeolitic material having an MWW-type framework structure from the synthesis mixture obtained from (iii.1) thereby obtaining a tin-containing zeolitic material having an MWW-type framework structure in its mother liquor; (iii.3) separating the tin-containing zeolitic material having an MWW-type framework structure obtained from (iii.2) from its mother liquor; (iv) treating the tin-containing zeolitic material having an MWW-type framework structure obtained from (iii) with an aqueous solution having a pH of at most 5 thereby obtaining the Sn-MWW having an Sn content of at most 2 weight-%, calculated as element and based on the weight of the Sn-MWW, and optionally separating the Sn-MWW from the aqueous solution.