Role Of CO2 As a Soft Oxidant For Dehydrogenation of Ethylbenzene to Styrene over a High-Surface-Area Ceria Catalyst

Catalytic performance and the nature of surface adsorbates were investigated for high-surface-area ceria during the ethylbenzene oxidative dehydrogenation (ODH) reaction using CO2 as a soft oxidant. The high surface area ceria material was synthesized using a template-assisted method. The interactions among ethylbenzene, styrene, and CO2 on the surface of ceria and the role of CO2 for the ethylbenzene ODH reaction have been investigated in detail by using activity test, in situ diffuse reflectance infrared and Raman spectroscopy. CO2 as an oxidant not only favored the higher yield of styrene but also inhibited the deposition of coke during the ethylbenzene ODH reaction. Ethylbenzene ODH reaction over ceria followed a two-step pathway: ethylbenzene is first dehydrogenated to styrene with H2 formed simultaneously, and then CO2 reacts with H2 via the reverse water gas shift. The produced styrene can easily undergo polymerization to form polystyrene, which is a key intermediate for coke formation. In the absence of CO2, the produced polystyrene transforms into graphite-like coke at temperatures above 500 °C, which leads to catalyst deactivation. In the presence of CO2, the coke deposition can be effectively removed via oxidation with CO2.