Abstract
Two series of catalysts were prepared by sol-gel and microemulsion synthetic procedure (SG and ME, respectively). Each series includes both pure Mg and Zr solids as well as Mg-Zr mixed solids with 25%, 50% and 75% nominal Zr content. The whole set of catalysts was characterized from thermal, structural and surface chemical points of view and subsequently applied to the liquid-phase xylose dehydration to furfural. Reactions were carried out in either a high-pressure autoclave or in an atmospheric pressure multi-reactor under a biphasic (organic/water) reaction mixture. Butan-2-ol and toluene were essayed as organic solvents. Catalysts prepared by microemulsion retained part of the surfactant used in the synthetic procedure, mainly associated with the Zr part of the solid. The MgZr-SG solid presented the highest surface acidity while the Mg3Zr-SG one exhibited the highest surface basicity among mixed systems. Xylose dehydration in the high-pressure system and with toluene/water solvent mixture led to the highest furfural yield. Moreover, the yield of furfural increases with the Zr content of the catalyst. Therefore, the catalysts constituted of pure ZrO2 (especially Zr-SG) are the most suitable to carry out the process under study although MgZr mixed solids could be also suitable for overall processes with additional reaction steps.
Highlights
Nowadays, one of the priorities of scientists is the search for alternatives to non-renewable energies
The results described above point out that the Zr sites are responsible for the dehydration of xylose to furfural, whereas the Mg related sites are not active at this point
This only implies a slight reduction in the conversion of xylose because, as mentioned, it is the ZrO2 component that is responsible for the catalytic activity of the MgO-ZrO2 mixed oxides
Summary
One of the priorities of scientists is the search for alternatives to non-renewable energies. A renewable solution for this challenge is biomass, which can provide both energy [1] and useful chemical compounds for industry [2]. Only 3% of the produced biomass is utilized for human-derived applications [3]. The transformation of biomass into platform molecules that can be further converted into high-added value chemicals is a hot topic nowadays [4,5]. Biomass is composed by carbohydrates (75%), lignin (20%) and a mixture of triglycerides, proteins and terpenes (5%) [5]. Lignocellulose is the main constituent of plant cell walls whose hydrolysis yields a mixture of C5 and C6 sugars as well as aromatic compounds (lignin). Valorization of pentoses and hexoses, such as xylose or glucose, is very interesting from the chemical point of view [4]
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