Synthesis and characterization of a mesoporous cerium oxide catalyst for the conversion of glycerol

Abstract

CeO₂ mesoporous materials were synthesized employing the “hard and soft template” technique. Ceria catalysts have been prepared by a nanocasting procedure using SBA-15 and KIT-6 silica-based templates and Pluronic P123 and F127 for the “soft template” technique. The mesoporous CeO₂ was characterized by techniques such as N₂ physisorption, which confirmed a mesoporous size pore system and transmission electron microscopy, TEM, which confirmed the material ordered pore structure. TGA/DTA analysis was used to determine the loss of weight compared to the temperature before and after the elimination of the template. On the other hand, by means of IR spectroscopy of the Ce-KIT-6 material, the partial elimination of the Si template after the NaOH treatment was confirmed by decreasing the peaks corresponding to the vibration bands of the Si-O-Si linkages. Finally, by temperature-programmed desorption (TPD) of NH₃ and CO₂, the acid and basic strength of the catalysts were determined, respectively. All samples exhibited much higher total basicity relative to total acidity. The analysis of TPR-H₂ showed regions of low temperature (350-400ºC) where the reduction of the bulk is plausible to be initiated and of high temperature (550ºC) of superficial reduction of the ceria.The performance of the catalysts was evaluated in the dehydration reaction of glycerol in gas phase at 320 ºC. The mesoporous CeO₂ material was selective to acetol and reached a 100% conversion of glycerol. The catalyst prepared by the “soft template” technique (CeO₂-P123) was the most selective to acetol (76%) with a 12% selectivity to acrolein. With the catalyst prepared by the “hard template” technique (Ce-KIT-6), the selectivity towards acetol was 48% and 22% towards acrolein. The acid properties of CeO₂ were found to be a determining factor for the selectivity to acetol and acrolein.