The development of new and improved processes for the synthesis of bio-based chemicals is one of the scientific challenges of our time. These new discoveries are not only important from an environmental point of view, but also represent an important economic opportunity, provided that the developed processes are selective and efficient. Bioethanol is currently produced from renewable resources in large amounts and, in addition to its use as biofuel, holds considerable promise as a building block for the chemical industry. Indeed, further improvements in production, both in terms of efficiency and feedstock selection, will guarantee availability at competitive prices. The conversion of bioethanol into commodity chemicals, in particular direct 'drop-in' replacements is, therefore, becoming increasingly attractive, provided that the appropriate (catalytic) technology is in place. The production of green and renewable 1,3-butadiene is a clear example of this approach. The Lebedev process for the one-step catalytic conversion of ethanol to butadiene has been known since the 1930s and has been applied on an industrial scale to produce synthetic rubber. Later, the availability of low-cost oil made it more convenient to obtain butadiene from petrochemical sources. The desire to produce bulk chemicals in a sustainable way and the availability of low-cost bioethanol in large volumes has, however, resulted in a renaissance of this old butadiene production process. This paper reviews the catalytic aspects associated with the synthesis of butadiene via the Lebedev process, as well as the production of other, mechanistically related bulk chemicals that can be obtained from (bio)ethanol.

The preparation method greatly influences morphology, acid–base properties and performance of SiO2–MgO catalysts. Wet-kneaded catalysts possess an improved distribution, proximity and strength of acidic-basic sites, thus leading to higher butadiene yields.

Silica-magnesia (Si/Mg=1:1) catalysts were studied in the one-pot conversion of ethanol to butadiene. The catalyst synthesis method was found to greatly influence morphology and performance, with materials prepared through wet-kneading performing best both in terms of ethanol conversion and butadiene yield. Detailed characterization of the catalysts synthesized through co-precipitation or wet-kneading allowed correlation of activity and selectivity with morphology, textural properties, crystallinity, and acidity/basicity. The higher yields achieved with the wet-kneaded catalysts were attributed to a morphology consisting of SiO2 spheres embedded in a thin layer of MgO. The particle size of the SiO2 catalysts also influenced performance, with catalysts with smaller SiO2 spheres showing higher activity. Temperature-programmed desorption (TPD) measurements showed that best butadiene yields were obtained with SiO2-MgO catalysts characterized by an intermediate amount of acidic and basic sites. A Hammett indicator study showed the catalysts' pK(a) value to be inversely correlated with the amount of dehydration by-products formed. Butadiene yields could be further improved by the addition of 1 wt% of CuO as promoter to give butadiene yields and selectivities as high as 40% and 53%, respectively. The copper promoter boosts the production of the acetaldehyde intermediate changing the rate-determining step of the process. TEM-energy-dispersive X-ray (EDX) analyses showed CuO to be present on both the SiO2 and MgO components. UV/Vis spectra of promoted catalysts in turn pointed at the presence of cluster-like CuO species, which are proposed to be responsible for the increased butadiene production.

Dehydrogenation promoters greatly enhance the performance of SiO 2 −MgO catalysts in the Lebedev process. Here, the effect of preparation method and order of addition of Cu on the structure and performance of Cupromoted SiO 2 −MgO materials is detailed. Addition of Cu to MgO via incipient wetness impregnation (IWI) or coprecipitation (CP) prior to wet-kneading with SiO 2 gave similar butadiene yields (∼40%) as when Cu was added to the already wet-kneaded catalyst. In contrast, the catalyst prepared by impregnation of Cu on SiO 2 first proved to be the worst catalyst of the series. TEM, XRD, and XPS analyses suggested that, for all catalyst materials, Cu 2+ forms a solid solution with MgO. This was confirmed by UV−vis, XANES, and EXAFS data, with Cu being found in a distorted octahedral geometry. As a result, the acid−base properties, as determined by Pyridine-and CDCl 3 −IR as well as NH 3 -TPD, are modified, contributing to the improved performance. Operando XANES and EXAFS studies of the evolution of the copper species showed that Cu 2+ , the only species initially present, is extensively reduced to a mixture of Cu 0 and Cu + , leaving only a limited amount of unreduced Cu 2+ . This formation of Cu 0 is the result of the reducing environment of the Lebedev process and is thought to be mainly responsible for the improved performance of the Cu-promoted catalysts.

Wet-kneading is a technique commonly used for the synthesis of SiO 2 −MgO catalysts for the Lebedev ethanol-to-butadiene process, with catalyst performance known to depend heavily on the preparation parameters used in this method. Here, the large influence of Mg precursor and MgO content on morphology, chemical structure (as determined by TEM(-EDX), FT-IR, XRD and solid-state 1 H− 29 Si cross-polarized MAS NMR), and on catalyst performance is demonstrated. The Mg precursor used is found to influence the extent of magnesium silicate formation during wet-kneading, as estimated from TEM and FT-IR, which, in turn, was found to correlate with catalyst performance. Accordingly, the catalyst synthesized from a nanosized Mg(OH) 2 precursor (SiO 2 −MgO (III) nano ), showing the highest degree of chemical contact between the SiO 2 and MgO components, gave the highest butadiene yield. Variation of the Mg/Si ratio in a series of SiO 2 −MgO (III) nano materials showed a volcano-type dependence of the butadiene yield on MgO content. 1 H− 29 Si CP-MAS NMR studies allowed for the identification of the type and an estimation of the amount of magnesium silicates formed during wet-kneading. Here, we argue that the structural characteristics of the hydrous magnesium silicates, lizardite and talc, formed during catalyst preparation, together with the ratio of the magnesium silicates to MgO, determine the overall acid/base properties of the SiO 2 −MgO (III) nano catalyst materials and as a result, catalyst performance.

An efficient and highly sustainable Ullmann-type homocoupling of bromo- and chloroarenes, including the more challenging electron-rich chloroarenes (e.g., 4-chloroanisole), catalyzed by in situ generated Pd colloids, is carried out in aqueous medium under relatively mild conditions (temperatures ranging from 40 to 90 degrees C). Glucose is used as a clean and renewable reductant, while tetrabutylammonium hydroxide (TBAOH) acts as base, surfactant, and phase-transfer agent, creating a favorable environment for the catalyst. Pd nanoparticle sizes, morphology, and chemical composition are ascertained by TEM and XPS analyses.

This study presents a novel process of wood modification employing humins, i.e. polydisperse furanic macromolecules formed during sugar dehydration. Humin valorization is more and more in the spotlight, thanks to the increased research efforts being placed by industries on biomass valorization. Here, a water soluble liquid fraction of humins was employed to impregnate wood and was polymerized within the wood using heat. This so-called 'humination' process was compared with the more classical furfurylation, which consists of impregnating with furfuryl alcohol (FA), and the polymerization of FA inside the wood.Confocal laser scanning fluorescence microscopy proved that furanic entities contained in the liquid fraction of humins polymerized within the wood cell walls and resulted in fluorescence similar to that seen for furfurylated wood. The humin modified wood showed lower mass increase and identical dimensional stability compared to furfurylated wood after immersion in water. Both treatments resulted in higher hydrophobicity compared to untreated wood. The elastic modulus of humin treated wood, measured by dynamic mechanical analysis (DMA), was similar to that of furfurylated wood for T < 75°C and slightly higher than untreated wood. Finally, reaction-to-fire properties were investigated. Humin treated wood showed some advantages over furfurylated wood such as longer ignition time, slower heat release rate (−13%) and lower CO formation. This study demonstrates for the first time that humins can be used as an alternative to FA for wood modification to obtain enhanced wood products. † Electronic supplementary information (ESI) available. See

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