Chromia-alumina catalysts have been used for the dehydrogenation of alkanes and alkenes to form the corresponding olefins or di-olefins. Typically the process for such dehydrogenation is a cyclic process wherein the alkanes are passed over the chromia-alumina catalyst in a reactor during which time the feedstock is dehydrogenated to the olefin or di-olefin with the concomitant generation of coke on the catalyst. Subsequently, the catalyst is regenerated by passing a heated airstream through the coked catalyst, thereby oxidizing, or burning, the coke off of the catalyst. The catalyst bed is subsequently returned to dehydrogenation service. After a large number of regeneration cycles, the activity of the regenerated catalyst decreases. This fall-off in activity is measured by reduced conversion of the saturated feedstock and also by a reduction in the yield of coke on the catalyst. A certain amount of coke formation is required to provide adequate heat to the catalyst bed during the oxidative regeneration in order to maintain the heat balance. When the activity of the regenerated catalyst has fallen enough, the catalyst must be replaced with a fresh load of catalyst.
While the prior art contains examples of chromia-alumina dehydrogenation catalysts containing minor amounts of zinc, for example U.S. Pat. Nos. 2,375,402 and 2,395,875, the zinc has generally been added as a stabilizer to improve the physical resistance of the alumina to the high temperatures of the dehydrogenation reaction and regeneration. Additionally zinc has been added to cracking catalysts to overcome the results of metal contaminants deposited on the catalyst. U.S. Pat. No. 2,901,419 is representative of those wherein the effect of the zinc addition is said to reduce the coke fomation caused by the metal contaminants. U.S. Pat. No. 2,265,641 discloses a dehydrogenation catalyst comprising at least 50% ZnO.