Abstract: A process using a particular catalyst in the dehydrogenation of an alkyl aromatic compound, e.g., ethylbenzene, to form a vinyl aromatic compound, e.g., styrene. The catalyst comprises a calcination product of (a) at least one iron oxide; (b) at least one carbonate, bicarbonate, oxide or hydroxide of potassium and/or cesium; (c) an oxide, carbonate, nitrate or hydroxide of cerium, or a mixture of at least two thereof; (d) an hydraulic cement; (e) an hydroxide, carbonate, bicarbonate, acetate, oxalate, nitrate, or sulfate of sodium, in an amount sufficient to provide from 0.2 to 10 percent sodium, calculated as sodium oxide, by weight of the calcined catalyst; and (f) a carbonate, sulfate, or hydroxide, of calcium or a mixture of at least two thereof, in an amount sufficient to provide from 1.5 to 20 percent calcium, calculated as calcium oxide, by weight of the calcined catalyst. The catalyst has improved moisture stability compared to catalysts in which at least one of (e) or (f) is not met.