Two-step hydrothermally synthesized Ce1-xZrxO2 for oxidative dehydrogenation of ethylbenzene with carbon dioxide

Ceria, zirconia, Ce0.9Zr0.1O2, Ce0.75Zr0.25O2, and Ce0.5Zr0.5O2 samples were synthesized via the two-step hydrothermal method by using Ce(NO3)(3)center dot 6H(2)O and Zr(NO3)(4)center dot 5H(2)O as the precursors, respectively. The oxides were applied as catalysts for the dehydrogenation of ethylbenzene by using carbon dioxide as a soft oxidant (CO2-ODEB) at 550 degrees C and 0.1 MPa. Reaction results indicate that ceria was the most active catalyst while the zirconia with a cubic structure was inactive for CO2-ODEB. In the cases of the oxides by inserting Zr into CeO2, the activity indexed by either the initial ethylbenzene (EB) conversion or the calculated turnover frequency (TOF) at a time on stream of 1 h was changed in the sequence of Ce0.9Zr0.1O2> > Ce0.75Zr0.25O2> Ce0.5Zr0.5O2 while the decreasing pattern of the stability was observed in the order of Ce0.5Zr0.5O2 approximate to Ce0.75Zr0.25O2> > Ce0.9Zr0.1O2. As revealed from the characterization results of XRD and Raman, the pure cubic solid solution of Ce1-xZrxO2 without any phase separations was obtained irrespective of the compositions. By correlating the characterization results, the activity of Ce1-xZrxO2 for CO2-ODEB was determined by the amount of the Ce3+ oxidized by CO2 and the rate of Ce3+/Ce4+ redox cycles. Moreover, both the coking rate and the promoting effect of the deposited coke on CO2-ODEB were responsible for the stability of Ce1-xZrxO2.