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Role of Promoters on Stability and Activity of Potassium Promoted Iron Oxide Dehydrogenation Catalysts

Zheng Li, Department of Chemical and Biological Engineering, Iowa State Univeristy, 3123 Sweeney Hall, Iowa State University, Ames, IA 50011 and Brent H. Shanks, Department of Chemical and Biological Engineering, Iowa State University, 2119 Sweeney Hall, Ames, IA 50011.

Potassium-promoted iron oxides are the primary catalysts used to produce styrene for dehydrogenation of ethylbenzene to styrene. Potassium serves a crucial role in enhancing the activity of the catalyst as well as improving catalyst stability. In addition to potassium, various other promoters are added to the catalyst to enhance its stability, activity and selectivity. Two promoters that were historically used in these catalyst systems were chromium (Cr) and vanadium (V). It is generally accepted that Cr is a structure stabilizer for the catalyst. While V can greatly increase the selectivity of the dehydrogenation catalyst it has a detrimental effect on the stability and activity of the catalyst. Further improvement in dehydrogenation catalysts will be predicated on producing catalytic materials with enhanced stability. Since the effects of Cr and V on stability are known and opposite, they are useful promoters for better understanding the underlying mechanism around dehydrogenation catalyst stability. In this work, the effects of Cr and V on the stability and activity of the catalyst system was investigated. The dehydrogenation reaction is complicated, with a range of gas phase compositions in addition to the potential for formation of “coke” on the catalyst surface. Therefore, experiments were performed in a thermogravimetric analyzer under H2, CO2, and ethylbenzene environments. Additionally, the function of steam was also studied. X-ray diffraction was applied to characterize the phase changes and the complementary quantitative calculations were conducted to determine their weight fraction. The results will be compared to potassium-promoted iron oxide without any other promoters.