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

摘要

Variety of rare earth oxide-doped CeO2/gamma-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/gamma-Al2O3 catalysts, 15 wt% CeO2/gamma-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/gamma-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/gamma-Al2O3 catalysts compared with the bare CeO2/gamma-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-delta) 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, H-2-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 O-2 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.