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Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural in Aqueous Medium over Nb₂O₅-Based Catalysts.

ABSTRACT: The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water was performed in the presence of pristine Nb₂O₅ and composites containing Nb and Ti, Ce or Zr oxides. In all experiments, fructose was converted to HMF using water as the solvent. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, N₂ physical adsorption, infrared and Raman spectroscopy and temperature-programmed desorption of NH₃. Experimental parameters such as fructose initial concentration, volume of the reacting suspension, operation temperature, reaction time and amount of catalyst were tuned in order to optimize the catalytic reaction process. The highest selectivity to HMF was ca. 80% in the presence of 0.5 g·L^-1 of bare Nb₂O₅, Nb₂O₅-TiO₂ or Nb₂O₅-CeO₂ with a maximum fructose conversion of ca. 70%. However, the best compromise between high conversion and high selectivity was reached by using 1 g·L^-1 of pristine Nb₂O₅. Indeed, the best result was obtained in the presence of Nb₂O₅, with a fructose conversion of 76% and a selectivity to HMF of 75%, corresponding to the highest HMF yield (57%). This result was obtained at a temperature of 165° in an autoclave after three hours of reaction by using 6 mL of 1 M fructose suspension with a catalyst amount equal to 1 g·L^-1.

SUBMITTER: Garcia-Lopez EI

PROVIDER: S-EPMC8308375 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40-68%. In case of desilicated zeolites, at 270-290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a "1" diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature. It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of "swiss cheese". Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M-10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M-10c). The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210 °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230 °C, 250 oC and 270 °C.

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Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural in Aqueous Medium over Nb₂O₅-Based Catalysts.

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Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural in Aqueous Medium over Nb₂O₅-Based Catalysts.