Unique influence of rare earth (Pr, Nd, and Er) oxide surface acidic texture over CeO₂/γ-Al₂O₃ catalysts for selective production of styrene using CO₂ flow

Abstract

Variety of rare earth oxide-doped CeO₂/γ-Al₂O₃ catalysts were prepared by a wet impregnation method and evaluated for oxidative dehydrogenation of ethylbenzene (EB) using CO₂ as soft oxidant in vapor-phase atmospheric-pressure conditions. Amongst the bare CeO₂/γ-Al₂O₃ catalysts, 15 wt% CeO₂/γ-Al₂O₃ exhibited excellent catalytic activity with noteworthy EB conversion and styrene selectivity. After incorporation of 3 wt% Er₂O₃, Pr₂O₃, or Nd₂O₃ oxide onto the 15 wt% CeO₂/γ-Al₂O₃ (15CA) catalyst, unusual catalytic properties were observed in terms of formation of active solid-solution species. The greater fraction of CO₂ molecule activation and dissociation phenomenon on the surface rare earth-doped CeO₂/γ-Al₂O₃ catalysts compared with the bare CeO₂/γ-Al₂O₃ catalyst were investigated. Among the rare earth-doped catalysts, 3ErCA showed superior mobile oxygen storage capacity and high CO₂ utilization ability, along with optimal surface acidic properties compared with the rare earth solid-solution properties of (Ce_xRE_1−xO_2−δ) Pr₂O₃ and Nd₂O₃ species. Moreover, the better catalytic activity of Er₂O₃ species can be explained on the basis of active metal–support synergistic interactions and noticeable surface acidic nature. All the catalysts were characterized by X-ray diffraction analysis, Brunauer–Emmett–Teller (BET) surface area measurements, H₂-temperature programmed reduction, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy, temperature-programmed desorption (NH₃-TPD), scanning electron microscopy (SEM), and CO₂ and O₂ pulse chemisorption techniques to elucidate the metal oxide composition and influence of rare earth clusters such as Pr₂O₃, Nd₂O₃, and Er₂O₃ oxides on the catalytic activity.