Proton-Conducting Perovskites as Supports for Cr Catalysts in Short Contact Time Ethane Dehydrogenation

Abstract

Proton-conducting oxides, BaZrO3 (BZ) and BaCeO3 (BC), were investigated as potential support materials for Cr catalyst (0.2–0.6 wt % Cr, Cr/BZ or BC) in ethane dehydrogenation at short contact times. The catalytic activity, selectivity in ethane dehydrogenation, and carbon formation were determined. A higher ethylene formation rate was obtained on Cr/BZ in comparison to Cr/BC: 1.4 × 10–7 and 6.2 × 10–8 mol/m2 s at 575 °C at 1 min on stream for 1 g of 0.2 Cr/BZ and 0.2 Cr/BC, respectively. The selectivity was maintained above 94% over all samples in the temperature range 475–575 °C. The catalytic activity toward ethane dehydrogenation was more than 1 order of magnitude higher for the proton-conducting supports when in comparison to a Cr/γ-Al2O3 catalyst with similar surface Cr coverage. X-ray photoelectron spectroscopy (XPS) revealed an initially higher concentration of Cr6+ on Cr/BC in comparison to Cr/BZ, corresponding to a plateau of relatively high activity at short times on stream. This plateau is attributed to oxidation of surface carbon species as they form via reduction of Cr6+ to Cr3+. All of the catalysts show deactivation through carbon deposition; however, the higher activity of proton-conducting supports may enable commercial operation at reduced temperature and thus reduced coke formation. A decreased residence time led to a significant increase of ethylene concentration at the reactor outlet with an associated decrease in carbon formation. Addition of H2 to the reactant feed further suppressed carbon formation but resulted in a significant decrease in ethylene formation rate.