The invention relates to a process for regenerating catalysts containing mixed oxides from the group of alkali metal and/or alkaline earth metal oxides, aluminium oxide and silicon oxide, characterized in that the regeneration comprises the following features: i) treatment of the catalyst in situ, ii) contacting of the catalyst with water, iii) treatment of the catalyst within a temperature range from 100 to 400° C., iv) treatment of the catalyst within a pressure range from 0.1 to 2 MPa, v) treatment of the catalyst over a period of 0.1 to 24 h, vi) treatment of the catalyst with a specific catalyst hourly space velocity of 0.1 to 100 h−1.