Mixed oxide and phosphoric oxide catalysts are prepared and used to increase the yields of light alkenes (especially ethylene and propylene) from steam cracking of light hydrocarbons, especially light naphtha. The oxide and phosphoric oxide catalysts are of general formulas CrZrjAkOx and CrZrjAkPlOx, in which: (1) j is between 0.5 and 120, k is between 0 and 50 (for oxides), (2) j is between 0.1 and 50, k is bewtween 0 and 30, and l is between 0.5 and 100 (for phosphates), and (3) A is a transition metal selected from Ti, Nb, Mo, V, Co, Ni, W, Fe, and can include rare earth metals. The metal precursors can be prepared from such precursors as sulfates, nitrates, oxalates, halides, chlorides, salts, acids, oxides, hydroxides, and alkoxides. Steam cracking is typically carried out at 600-1000 degrees, steam-hydrocarbon weight ratio 0.3-1.0:1, and space velocity 1-20 h-1.
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