Provided is a method for preparing a solution B comprising at least one catalyst in at least one second solvent, comprising at least the following steps of (A) providing a solution A comprising the at least one catalyst in at least one first solvent, (B) treating the solution A from step (A) with activated carbon, (C) removing the activated carbon from the solution A, and (D) exchanging the at least one first solvent in solution A for at least one second solvent in order to obtain the solution B comprising the at least one catalyst in at least one second solvent, to a solution of at least one catalyst in at least one second solvent, obtainable by the method according to the invention, to the use of this solution for preparing a composition comprising the at least one catalyst, the at least one second solvent, at least one polyisocyanate and at least one NCO-reactive compound, to the use of this composition for producing a single-layered or multi-layered coating system and a corresponding process.