Defect-rich Ce1-xZrxO2 solid solutions for oxidative dehydrogenation of ethylbenzene with CO2

Abstract

The zirconium doped ceria (Ce1-xZrxO2, x = 0.0, 0.1, 0.3, 0.5, 0.9, and 1.0) was synthesized via the urea-hydrolysis assisted hydrothermal method by using (NH4)2Ce(NO3)6 and ZrO(NO3)2·2H2O as the precursors. The structural and textural properties of the oxides were characterized with pertinent techniques, and the materials were evaluated as catalysts for the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO2-ODEB) under the conditions of 550 °C, 0.1 MPa, CO2 to ethylbenzene molar ratio of 20, and W/F = 8.07 g-cat·h∙mol−1. Characterization results indicate that the single-phase cubic solid solution was formed in the cases of Ce0.9Zr0.1O2, Ce0.7Zr0.3O2, and Ce0.5Zr0.5O2. In contrast, separated tetragonal and monoclinic phases of ZrO2 were present over Ce0.1Zr0.9O2 besides the solid solution. Moreover, the relative content of defects over the surface of Ce1-xZrxO2 was continuously increased with x, but the highest amount of reducible Ce4+ was obtained over Ce0.5Zr0.5O2. Reaction results indicate that Ce1-xZrxO2 was effective for CO2-ODEB, and the highest conversion of ethylbenzene was obtained over Ce0.5Zr0.5O2. The activity of Ce1-xZrxO2 for the titled reaction is determined by both the amount of the reducible Ce4+ and the easy oxidation of Ce3+ by CO2 over the catalyst. The inhibition of the coke via the oxidation of Ce3+ by CO2 and its promotional effect on the activity are responsible for the stability of the catalyst for CO2-ODEB.