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 (CexRE1−xO2−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.