Role of Cr and V on the stability of potassium-promoted iron oxides used as catalysts in ethylbenzene dehydrogenation

Potassium-promoted iron oxides are the most widely used catalysts for catalytic dehydrogenation of ethylbenzene to styrene. Besides potassium, other minor promoters are also added into the catalyst for different purposes, either enhancing catalyst stability or activity/selectivity. Chromium (Cr) and vanadium (V) are two historically used promoters. Cr is widely accepted to be a structure stabilizer and V can increase the selectivity to styrene but with detrimental effect on stability and activity of the catalysts. Since the effects of these two promoters are known and opposite, the effects of Cr and V on the solid state phase behavior of K-promoted iron oxide were investigated. Gas environments consisting of H2, CO2, ethylbenzene and steam were used to explore the interaction between the gas composition and the phase behavior of the doped iron oxides. The experiments were performed in a thermogravimetric analyzer under various gas environments and X-ray powder diffraction was used to quantitatively characterize the phase changes. The Cr and V promoted K–promoted iron oxide had very different responses to the different gas phase environments, but in the presence of steam and ethylbenzene Cr stabilized the iron oxide against reduction whereas V destabilized the iron oxide. These data support the idea that the promoters influence K-promoted iron oxide stability under low steam-to-ethylbenzene operation via modifying the phase behavior of the iron oxide.

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► K-promoted iron oxide stability impacted by gas phase species.
► Cr stabilizes K–Fe2O3 against reduction.
► V destabilizes K–Fe2O3 oxide via interaction with the K.
► Phase change behavior of K–Fe2O3 correlates with reaction performance.