(707f) Zr Doping Effect On CeO2 As the Catalyst in the CO2 – Ethylbenzene Reaction

Under the thermodynamic limitation , dehydrogenation of ethylbenzene (EB) to styrene (ST) with CO₂ is widely investigated. The lattice oxygen mobile capacity of catalyst is the important influencing factors in the CO₂-EB reaction. CeO₂ of the CaF₂ structure with the excellent oxygen storage/release capacity (OSC) is preferred as the catalyst. The addition of Zr⁴⁺ to the cubic structure of CeO₂ can greatly increase the OSC and improve its surface area, thermal stability, mechanical strength and surface acidity. The Zr content of Ce_xZr_1-xO₂ solid solutions strongly influence the crystal structure, the mobility of lattice oxygen and the catalytic performance. Ce_xZr_1-xO₂ solid solutions replacing the pure CeO₂ as the catalyst could be used in oxidative dehydrogenation of EB to ST with CO₂ for changing the lattice structure of CeO₂ and improving the transmission capacity of lattice oxygen.

In this work, Ce_xZr_1-xO₂ solid solutions with different Zr proportions were synthesized using hydrothermal method. The synthesized catalysts were characterized by X-ray power diffraction pattern, Raman spectroscopy and N₂-adsorption. It was found that the catalysts were solid solution mixture having specific surface area more than 100 m²/g. By the means of the H₂ temperature-programmed reduction, the lattice oxygen mobile capacity was calculated, corresponding to the order is Ce_0.5Zr_0.5O₂ > Ce_0.7Zr_0.3O₂ > Ce_0.3Zr_0.7O₂ > CeO₂. The performance of the catalysts for dehydrogenation of EB to ST was evaluated in a fixed-bed reactor under the conditions 823 K, 1 atm, and 20 of the CO₂/EB molar ratio. Results showed that the lattice oxygen mobile capacity of Ce_xZr_1-xO₂ influenced the catalytic activity and promoted activity of CO₂. The Ce_0.5Zr_0.5O₂ showed the highest activity with the EB conversion of 50% and the ST selectivity above 96%. The mechanistic model of EB dehydrogenation with CO₂ over the Ce_xZr_1-xO₂ catalysts was proposed.