The invention relates to multi-metal oxides of general formula (I) Mo12-a-b-c Va M<1>b M<2>c Ox, wherein the variables have the following meaning: M<1> = W and/or Nb, M<2> = Ti, Zr, Hf, Ta, Cr, Mn, Re, Ag, Cu, Si, and/or Ge, a = 0.1-6, b... HARTMUT HIB...