The present invention relates to silver-containing and optionally promoter-containing supported catalysts and catalyst intermediates, processes for their preparation and their use for preparing alkylene oxides by oxidation of alkenes with oxygen. The catalysts are prepared by treatment of a support with a lactic acid containing silver ions, nitrate ions and optionally promoter metal ions, drying, predecomposition in a virtually oxygen-free atmosphere and subsequent activation by heating in an oxygen-containing atmosphere while precisely controlling the temperature conditions and the feeding-in of oxygen. The catalyst intermediates obtainable by treatment, drying and only predecomposition can be activated in a temporally and physically separate process step to form the actual catalysts. Suitable promoters are alkaline earth metal compounds and/or alkali metal compounds. High activities and high selectivities are achieved when using the catalysts of the invention for preparing alkylene oxides.