Insights into the improvement effect of Fe doping into the CeO2 catalyst for vapor phase ketonization of carboxylic acids

Abstract

The conversion of carboxylic acid through ketonization process reduces O-atoms and increases CC bonds, which can provide attractive routes for upgrading biomass feedstocks into biofuels. The key factors influencing the surface ketonization activity over CeO2-based oxides catalysts remain matters of active discourse. Here, a series of Ce1-xFexO2-δ catalysts were investigated for vapor-phase ketonization of acetic and propionic acid. The catalysts were characterized in detail using various physico-chemical techniques both before and after reaction to gain understanding of the ketonization process. The turnover frequency (TOF) based on the basic sites changed with the Fe content. The Ce0.8Fe0.2O2-δ sample showed the prominent ketonization activity with the highest TOF value. On one hand, for samples with a lower Fe addition (x<0.3), the formed CeO2-like solid solution with numerous Ce-O-Fe species showed a dramatic increase in surface oxygen vacancies. These oxygen vacancies were beneficial to catalytic performance. Moreover, the superior redox properties with weaken MO bonds of Ce-O-Fe species thereby promote the ketonization activity. On the other hand, the higher Fe addition (x>0.3) caused the damage of the Ce-O-Fe structure, thus reducing ketonization activity. Notably, the investigation of the reaction temperature regime of Ce0.8Fe0.2O2-δ sample directly proved the existence of surface redox cycle during the ketonization process.