Investigation of CeO2, MoO3, and Ce2(MoO4)3, Synthesized by the Pechini Method, as Catalysts for Fructose Conversion

Abstract

Cerium oxide (Ce100), molybdenum oxide (Mo100), and a material containing Ce and Mo (CeMo) were synthesized by the Pechini method, using glycerol as a polyol. These materials were applied for fructose conversion in an aqueous medium. The characterization results show the formation of cerium molybdate (Ce2(MoO4)3) for CeMo. Ce100 presented good thermal stability, and Mo100 sublimation of MoO3 and polymolybdates was verified. CeMo exhibited a mass loss of 19%, associated with the sublimation of MoO3 and polymolybdate species. Additionally, the existence of Bronsted and Lewis acid sites was confirmed, and the addition of Mo to Ce was an efficient strategy to increase the acidity. Regarding the catalytic activity (150 °C and 0.5 to 6 h), Ce100 exhibited low conversions and high selectivity to 5-hydroxymethylfurfural (5-HMF). For Mo100, high conversions, with a significant formation of insoluble materials, were detected. For CeMo, beyond the high activity, a lower formation of insoluble materials was noted. In this case, selectivity toward products from the retro–aldolic route and 5-HMF were obtained. These results indicate that the main factor influencing fructose conversion is an adequate combination of the acid sites. Recycling experiments were carried out, and stability was observed for four cycles, confirming the robustness of this system.

Recent advancements in CeO2-enabled liquid acid/base catalysis

“…In addition, CeO 2 has also been employed in the dehydration of fructose to produce 5-hydroxymethylfurfural (5-HMF), which is recognized as a bio-refining intermediate for the manufacture of alternative fuels. 74,75 Very recently, the catalytic performance for the production of 5-HMF on CeO 2 , MoO 3 , and Ce 2 (MoO 4 ) 3 was thoroughly studied. 75 It was found that an adequate combination of acid sites is of great significance to ensure both activity and selectivity to the target product.…”

“…74,75 Very recently, the catalytic performance for the production of 5-HMF on CeO 2 , MoO 3 , and Ce 2 (MoO 4 ) 3 was thoroughly studied. 75 It was found that an adequate combination of acid sites is of great significance to ensure both activity and selectivity to the target product. Both Brønsted and Lewis acidic sites were confirmed on the three catalysts, among which CeO 2 possessed the lowest number of acidic sites, exhibiting the lowest conversion of fructose and the highest selectivity to 5-HMF as a result.…”