Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6–C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Furfural has been considered as one of the most promising platform molecules directly derived from biomass. The hydrogenation of furfural is one of the most versatile reactions to upgrade furanic components to biofuels. For instance, it can lead to plenty of downstream products, such as (tetrahydro)furfuryl alcohol, 2-methyl(tetrahydro)furan, lactones, levulinates, cyclopentanone(l), or diols, etc. The aim of this review is to discuss recent advances in the catalytic hydrogenation of furfural towards (tetrahydro)furfuryl alcohol and 2-methyl(tetrahydro)furan in terms of different non-noble metal and noble metal catalytic systems. Reaction mechanisms that are related to the different catalytic materials and reaction conditions are properly discussed. Selective hydrogenation of furfural could be modified not only by varying the types of catalyst (nature of metal, support, and preparation method) and reaction conditions, but also by altering the reaction regime, namely from batch to continuous flow. In any case, furfural catalytic hydrogenation is an open research line, which represents an attractive option for biomass valorization towards valuable chemicals and fuels.

Lignin in advanced energy applications: source, extraction methodolgy, structure/property relationships.

A wide majority of the organic–inorganic hybrid perovskites employed in photovoltaics contain Pb, which is a negative issue due to its high toxicity and the low stability of the Pb-based three-dimensional (3D) perovskites. The double perovskites or “elpasolites” with the formula A₂BB′X₆ arise as an alternative to avoid the use of Pb, however, not many of the theoretically predicted structures have been synthesized so far due to several synthetic issues, such as, the formation of stable side products. Herein, we report the synthesis of three double perovskites, Cs₂AgBiBr₆, MA₂TlBiBr₆ and Cs₂AgSbBr₆, through a highly efficient and reproducible mechanochemical approach: the high energy ball milling. This synthetic approach does not require the use of organic solvents, so it is a greener method compared to those reported for other double perovskites. The Cs₂AgBiBr₆ and MA₂TlBiBr₆ double perovskites were synthesized with high purity as proved by X-ray diffraction (XRD) and X-ray fluorescence (XRF) measurements. However, the Cs₂AgSbBr₆ double perovskite was obtained in mixture with Cs₃Sb₂Br₉, a side product of the reaction. Several attempts to prepare the Cs₂AgSbBr₆ double perovskite by using other synthetic methods have been unsuccessful due to the low formation enthalpy of the Cs₃Sb₂Br₉ side product and only the hydrothermal method afforded Cs₂AgSbBr₆ in mixture with other compounds. We believe that the low temperature required in the ball milling synthesis is the key factor that allows the formation of the antimony double perovskite. Cs₂AgSbBr₆ is a brown powder with a bandgap energy of 1.93 eV as shown with diffuse reflectance measurements. The three powders exhibit a very high stability with no changes at all in the crystal structure after several months of storage at room temperature and ambient humidity.