The addition of antimony ions to the potassium/ammonium salts of the 12-molybdophosphoric acid greatly enhanced the thermal structural stability of the Keggin-type heteropolyoxometalates. This unexpected property allowed to employ these materials as catalysts for the oxidative dehydrogenation of ethane to ethylene, a reaction which requires high temperatures. The doping of the compounds with other metal ions increased the activity and the selectivity to ethylene.