Niobium-loaded montmorillonite was employed as a highly efficient catalyst for the catalytic conversion of glucose to 5-HMF in a biphasic solvent.

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Purpose Lead contamination is ubiquitous, and much attention has been paid due to its toxicity. The phyllomanganate birnessite is the most common Mn oxide in soils. The MnO 6 octahedral layers may have significant Mn vacancies in the hexagonal birnessites. Among heavy metal ions, birnessites possess the greatest adsorption affinity and capacity for Pb 2+ . The aim of this study was to understand the relationship between vacant Mn octahedral sites and Pb 2+ adsorption. Materials and methods Birnessite synthesis was achieved by the reduction of potassium permanganate in a strong acidic medium. Synthetic birnessite was then treated with Mn 2+ or Zn 2+ at different concentrations. Isothermal Pb 2+ adsorption on birnessite before and after treatments was measured at a solid-to-liquid ratio of approximately 1.67 g/L, and Pb 2+ concentrations ranged from 0 to 10 mmol/L with an ionic strength of 0.1 mol/L NaNO 3 . The amount of Pb 2+ adsorbed and the amount of Mn 2+ or Zn 2+ released during the whole adsorption process were obtained by comparison with a control group without adding Pb 2+ . The amount of H + released was determined from the recorded additions of standard HNO 3 /NaOH solutions. Results and discussion Mn average oxidation state (AOS) and d(110)-interplanar spacings of the birnessites remained almost unchanged as the concentration of the treating Zn 2+ increased, indicating an unchanged number of vacant Mn octahedral sites, whereas the maximum Pb 2+ adsorption decreased from 3,190 to 2,030 mmol/kg due to the presence of Zn 2+ on adsorption sites. The AOS's of the Mn 2+ -treated birnessites decreased and most of the Mn 2+ ions added were oxidized to Mn 3+ ions. The d(110)-interplanar spacing of Mn 2+ -treated birnessites increased from 0.14160 to 0.14196 nm, indicative of a decreased vacant Mn octahedral sites. Moreover, the maximum Pb 2+ adsorption of Mn 2+ -treated birnessites decreased from 3,190 to 1,332 mmol/kg, the decrease being greater than that for the corresponding Zn 2+ -treated birnessites. Conclusions Most Mn 2+ was oxidized to Mn 3+ by birnessite, with a portion of Mn 3+ located above or below vacant sites, which did not affect the number of vacant sites, and the remaining Mn 3+ migrating to occupy the vacant sites. In contrast, Zn 2+ ions are adsorbed only above or below vacant sites. Birnessite Pb 2+ adsorption capacity is determined largely by the number of vacant Mn sites.

A 5-HMF yield of 96.7% was obtained over an excellent heterogeneous catalyst NbPW-06 in DMSO at 80 °C.

Abstract:The production of bio-diesel fuels from carbohydrates is a promising alternative to fossil fuels with regard to the growing severity of the environmental problem and energy crisis. Potential bio-diesel candidates or additives, such as 5-(hydroxymethyl)-2-(dimethoxymethyl) furan (HDMF), 2-(dimethoxymethyl)-5-(methoxymethyl) furan (DMMF), and 5-(methoxymethyl)-2-furaldehyde (MMF) could be produced from the alcoholic solutions of both 5-HMF and fructose in the presence of solid acid catalysts. In the present study, a readily prepared, silica, gel-supported nitric acid (SiO 2 -HNO 3 ) catalyst was found to be exceptionally reactive for the production of HDMF from fructose. A DMSO-methanol biphasic solvent system was developed and HDMF, DMMF, and MMF were observed at 150 • C, with maximum yields of 34%, 34%, and 25%, respectively. Meanwhile, a maximum HDMF yield of 77% was obtained from 5-HMF in methanol. Moreover, a sequential, one-pot, two-step dehydration/acetalization process, involving the dehydration of fructose to 5-HMF in dimethylsulfoxide (DMSO) at 150 • C, and followed by adding a certain amount of methanol to react with the formed 5-HMF to HDMF at 100 • C, was developed to promote the yield of HDMF. The optimum yield of HDMF reached 70% with the complete conversion of fructose. The reaction mechanisms of dehydration and acetalization have been proposed for the conversion of 5-HMF to HDMF. The two-step design allows for facile catalyst recycling while supplying as a promising method for the production of biodiesel from complex carbohydrates.