TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: the inorganic support is clays, inorganic oxides and/or spinels, preferably silica, and the Group VA metal or oxide is bismuth or bismuth oxide. The catalyst composition further comprises a first catalyst containing inorganic support with Group IVA metal or oxide preferably tin or oxides in amount 0.0001-5 especially 0.1-1.5 wt.%, and Group VIII metal or oxide, preferably platinum or oxides in amount 0.0001-5 especially 0.1-1.5 wt.%, and a second catalyst containing inorganic support and Group VA metal or oxide in amount 1-20 wt. %. The first support is zinc aluminate or calcium aluminate and the second support is silica. The first support is spinel of zinc, magnesium, iron, manganese, calcium, zirconium, molybdenum, ruthenium, rhenium, cobalt and/or germanium, and the second support is silica.Preferred Process: the composition is prepared by:(1) contacting first support with Group IVA compound;(2) heat treating the first composition to convert Group IVA compound to oxide;(3) contacting the composition with Group VIII compound;(4) contacting second composition with heat to produce composition A;(5) contacting a second inorganic support with Group VA compound to produce third composition B;(6) heat treating second composition and combining compositions A and B.The Group IVA compound is tri-n-butyltin, n-butyltin trichloride, di-n-butyldiphenyltin, di-n-butyltin diacetate, di-n-butyltin dichloride, di-tert-butyltin dichloride, di-n-butyltin dilaurate, dimethyldiphenyltine, diphenyltin dichloride, hexa-n-butyltin hexamethylditin, hexaphenyltin, methyltin trichloride, phenyltin trichloride, tetra-n-butyltin, tetraethyltin, tetramethyltin, tetraphenyltin, tetra-I-propyltin, tetra-n-propyltin, tin acetate, tin bromide, tin chloride, tin oxalate, tin sulphate and/or tin sulphide. The Group VA compound is acetate, bromide, chloride, 2-ethylhexanoate, fluoride, iodide, neodecanoate, nitrate, oxide, sulphide and/or titanate of bismuth or triphenylbismuth. The Group VIII compound is chloroplatinic acid, platinum chloride, platinum bromide, platinum iodide, tetramine platinum chloride, tetramine platinum nitrate, tetramine platinum hydroxide and/or tetrachlorodiamine platinum. Composition A is platinum- and tin-promoted zinc aluminate and calcium aluminate, and composition B is bismuth-promoted silica. A saturated hydrocarbon fluid, especially aliphatic hydrocarbon preferably propane, is contacted with the above composition to effect conversion to olefin. The contacting is in the presence of steam. EXAMPLE - A blend of Pt/Sn/Zn-Ca aluminate and bismuth oxide/silica catalyst composition have 19.3% conversion of propane after 3 hours, with 96.5% selectivity to propylene. This compared with 15.8% and 93.5%, respectively, for the Pt/Sn/Zn-Ca aluminate catalyst alone.