The invention relates to a method for separating and partially returning transition metals and/or catalytically effective complex compounds thereof from a reaction mixture by combining one at least one-stage membrane separation and an adsorption, wherein a current comprising a catalyst, comprising a transition metal, is divided over at least one one-stage membrane separation step in a transition metal enriched retentate stream that resupplies the reaction mixture and a transition metal depleted permeate stream and the transition metal depleted permeate stream is further supplied to an adsorption step. The invention further relates to a method for producing tridecanals.