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Polyoxometalate-based metal-organic frameworks (POMOFs) with bifunctional Lewis-Brønsted acid were designed by confining polyoxometalates (POMs: phosphotungstic acid (PW), phosphomolybdic acid (PMo) or silicotungstic acid (SiW)) within the Zr-MOFs. The confined POMs not only have their own Brønsted acid, but can also regulate the Lewis acid strength of the POMOFs via charge regulation, ultimately allowing the POMOFs to display superior catalytic performance in the tandem catalysis of furfural (FAL) to γ-valerolactone (GVL). Among the three catalysts (POMOF-PW, POMOF-PMo and POMOF-SiW), a complete conversion of FAL was achieved, while POMOF-PW exhibited the highest GVL yield (58.1 %) at 160 °C within 23 h. The leaching experiment and structural characterization of the catalyst before and after recycling confirmed the stability of the catalyst structure. The humin originates from the polymerization of furan ring-containing compounds driven by Brønsted acid. The adsorption configuration of the substrate molecules on the catalyst offers a new explanation for the tandem reaction process, i.e. that perpendicular adsorption performs only the first step of the tandem reaction, while the coexistence of perpendicular and horizontal adsorption permits the entire reaction process. This work gives unique insights into the tandem reaction of FAL and can guide the design of efficient tandem reaction catalysts. A synthetic strategy has been developed to construct polyoxometalate-based metal-organic framework (POMOF) with bifunctional Lewis-Brønsted acid sites by chemically confining polyoxometalates (POM) in metal-organic framework (MOF) channels. Confined POM not only endows the catalyst with Brønsted acid sites, but also enhances the acid strength of the catalyst through charge regulation, which finally promotes the catalyst to exhibit excellent catalytic performance in the multi-step cascade catalysis from furfural (FAL) to γ-valerolactone (GVL). This work also provides insight into the origin and driving sites of the by-product humin, as well as the role of the adsorption configuration in the catalytic process. A look into the future of the multi-step tandem reaction of FAL to GVL is presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Both one‐pot catalytic conversion of furfural (FAL) to isopropyl levulinate (PL) and carbonization of by‐product (humins) for electromagnetic wave absorption are discussed, which provides inspiration that humins can be applied to electromagnetic wave absorption. In the former, phosphotungstic acid (PW) is employed as a homogeneous catalyst to convert FAL to PL via a tandem reaction in one pot, with the formation of a vast amount of humins. With FAL and various intermediates as substrates, it was found that humins was a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl ester (FE) with furan rings. In addition, the in situ attenuated total reflection infrared (ATR‐IR) spectra also provided a basis for the proposed reaction route. In the latter, with the humins as raw material, P species and WO3 doped nano‐porous carbon (Humins‐700) platform formed after high‐temperature annealing is used for electromagnetic wave absorption and manifests desirable absorption performance. The minimum reflection loss (RLmin) value is −47.3 dB at 13.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth reaches 4.5 GHz (11.2–5.7 GHz). [ABSTRACT FROM AUTHOR]

A simple basic zirconium carbonate (BZC), which can be produced on a large scale in industry, was studied for hydrogen transfer of biomass-derived carboxides and exhibited excellent catalytic properties at low temperatures, especially for the conversion of furfural (FUR) to furfuryl alcohol (FFA). With the catalyst, the reduction reaction of FUR was efficiently performed at low temperatures (below 100 °C) and an FFA yield of 98.66% was obtained even at room temperature. When the temperature reached 180 °C, the yield of FFA quickly reached 90.29% within 15 minutes. During the reaction, the changes of the functional groups of the reactants and products were monitored by in situ ATR-IR spectroscopy in real time, which provided a basis for the proposed reaction mechanism. Further, the ATR-IR spectroscopy and XPS results of the different catalysts showed that BZC has the strongest acidity among all the comparative catalysts, which is consistent with its best catalytic performance. In addition, reaction kinetics were also studied. [ABSTRACT FROM AUTHOR]

Graphical abstract We prepared the catalysts through the ion-exchange of natural calcium montmorillonite with an aqueous aluminum trichloride solution. Al3+ was a good Lewis acid catalyzing the isomerization of glucose to fructose, and the partially hydrolyzed Al−OH groups acted as Brønsted acid for the dehydration of fructose to HMF, which can be extracted by THF with a high yield. Highlights • A series of Al-mont-n were prepared with ion-exchange method for conversion of carbohydrates to HMF. • The catalytic activity is dependent on the concentrations of Al3+ ion. • A high yield of HMF (80.4%) was produced from glucose. • 60.1% and 81.6% yield of HMF were obtained from the dehydration of starch and inulin, respectively. Abstract Aluminum ion-exchanged Ca-montmorillonite with different concentrations of aluminum ion were prepared and applied in the conversion of carbohydrates to 5-hydroxymethylfurfural (HMF). It was found that two types of acid sites were present in the catalyst, Lewis acid sites for isomerization of glucose and Brønsted acid sites for dehydration of fructose. With Al-mont-10 as catalyst, the yield of HMF converted from glucose was 80.4% in a biphase system (THF: NaCl solution) at 180 °C for 2.5 h. Further, the catalyst also shows excellent catalytic performance in the conversion of starch and inulin, and the yield of HMF reached 60.1% and 81.6% under identical conditions, respectively. [ABSTRACT FROM AUTHOR]

• Zirconium ion-intercalated montmorillonite was synthesized by a facile method. • The amount of Lewis and Bronsted acids could be altered by changing the concentration of zirconium ions. • One-pot cascade conversion of FAL to GVL was achieved under mild conditions. • Over 99% furfural conversion and 50.4% GVL yield were attained. A series of ultrathin metal intercalated montmorillonite (Mont) nanosheet materials were prepared and characterized for the one-pot cascade conversion of furfural (FAL) to obtain γ-valerolactone (γ-GVL). The coordination of the intercalated metal ions and the hydroxyl groups between the montmorillonite layers leads to an increase in the specific surface area and pore volume of the material, which coupled with the acidity of the metal ions themselves improves the catalytic performance of the material. Thus Zr-Mont-0.1 exhibited optimal catalytic performance with 100% conversion of FAL and 50.4% yield of GVL under mild conditions, and more importantly, the catalyst maintained its good catalytic performance after the fourth use. Meanwhile the number of Lewis and Brønsted acid sites in the Zr-Mont catalyst can be varied by adjusting the zirconium ion concentration. The proposed reaction mechanism provides initial insights into the role of metal-functionalized montmorillonite in catalyzing the reaction. In addition, the ten-fold magnification reaction confirmed the potential industrial application of the catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]