Constructing well-distributed cerium oxide nanoparticles on alumina-carbon nanosheet for boosting the synthesis of imine from benzyl alcohol and aniline

Abstract

Considering the unique redox property and the excellent oxygen storage-diffusion ability of CeO₂ nanoparticles as well as the advantages of large external surface area and accelerated mass transfer due to the open structure of two-dimensional nanosheets, well-distributed CeO₂ nanoparticles supported on alumina-carbon nanosheet catalysts, which were prepared by a facile impregnation and subsequent pyrolysis procedure, were investigated for the synthesis of imine from benzyl alcohol and aniline by using air as the sole oxidant. The physical and chemical properties of the synthesized Ce/ALC catalysts were characterized by various techniques. It was found that an Al–Ce–O solid solution could be formed between supported Ce and Al within ALC during the pyrolysis procedure. The formation of Al–Ce–O solid solution is beneficial for generating more defective sites, promoting to adsorb and activate oxygen. Therefore, the activity of Ce/ALC catalyst for oxidative coupling of benzyl alcohol and aniline was enhanced with the addition of alumina. An appropriate Al/Ce ratio could obtain a large amount of surface Ce³⁺ ions, more readily available oxygen species and balanced acid-base sites, which were very crucial for achieving a high imine yield. The Ce/ALC-2 catalyst with Al/Ce ratio of ∼7 exhibited the highest catalytic activity. After 8 h of reaction at 80 °C, the benzyl alcohol conversion reached 99 % with an imine yield of 99 %, and the productivity of imine was 2.48 mmol g_cat. ⁻¹h⁻¹. The coordinatively unsaturated Ce³⁺–V_ö defects were suggested as the active sites for the oxidative coupling of benzyl alcohol and aniline. In addition, this catalyst also exhibited good stability and recyclability, which might provide an alternative strategy for the oxidative coupling reaction.