Sustainable Alternatives for the Development of Thermoset Composites with Low Environmental Impact.

The current concerns of both society and the materials industries about the environmental impact of thermoset composites, as well as new legislation, have led the scientific sector to search for more sustainable alternatives to reduce the environmental impact of thermoset composites. Until now, to a large extent, sustainable reinforcements have been used to manufacture more sustainable composites and thus contribute to the reduction of pollutants. However, in recent years, new alternatives have been developed, such as thermosetting resins with bio-based content and/or systems such as recyclable amines and vitrimers that enable recycling/reuse. Throughout this review, some new bio-based thermoset systems as well as new recyclable systems and sustainable reinforcements are described, and a brief overview of the biocomposites market and its impact is shown. By way of conclusion, it should be noted that although significant improvements have been achieved, other alternatives ought to be researched.

Gas reactions under intrapore condensation regime within tailored metal-organic framework catalysts.

Production of 1-butene, a major monomer in polymer industry, is dominated by homogeneous protocols via ethylene dimerization. Homogeneous catalysts can achieve high selectivity but require large amounts of activators and solvents, and exhibit poor recyclability; in turn, heterogeneous systems are robust but lack selectivity. Here we show how the precise engineering of metal-organic frameworks (MOFs) holds promise for a sustainable process. The key to the (Ru)HKUST-1 MOF activity is the intrapore reactant condensation that enhances ethylene dimerization with high selectivity (> 99% 1-butene) and high stability (> 120 h) in the absence of activators and solvents. According to spectroscopy, kinetics, and modeling, the engineering of defective nodes via controlled thermal approaches rules the activity, while intrapore ethylene condensation accounts for selectivity and stability. The combination of well-defined actives sites with the concentration effect arising from condensation regimes paves the way toward the development of robust MOF catalysts for diverse gas-phase reactions.

Solvent and catalyst effect in the formic acid aided lignin-to-liquids.

The effect of the type of solvent, ethanol or water, and a Ru/C catalyst were studied in the formic acid aided lignin conversion. The best results were obtained in the presence of the Ru/C catalyst and using ethanol as solvent at 300 °C and 10 h (i.e. 75.8 wt% of oil and 23.9 wt% of solids). In comparison to the water system, the ethanol system yields a significantly larger amount of oil and, at 300 °C and 10 h, a smaller amount of solids. The main reasons for this positive effect of the ethanol solvent are i) the formation of ethanol-derived esters, ii) C-alkylations of lignin fragments and iii) the generation of more stable lignin derivatives. The Ru/C exhibits significantly higher lignin conversion activity compared to other Ni-based catalysts, especially at 300 °C, which is related to the enhanced activity of the Ru0 sites towards hydrogenolysis, hydrodeoxygenation and alkylation reactions.

Unraveling the Role of Formic Acid and the Type of Solvent in the Catalytic Conversion of Lignin: A Holistic Approach.

The role of formic acid together with the effect of the solvent type and their synergic interactions with a NiMo catalyst were studied for the conversion of lignin into bio-oil in an alcohol/formic acid media. The replacement of formic acid with H2 or isopropanol decreased the oil yield to a considerable degree, increased the solid yield, and altered the nature of the bio-oil. The differences induced by the presence of H2 were comparable to those observed in the isopropanol system, which suggests similar lignin conversion mechanisms for both systems. Additional semi-batch experiments confirmed that formic acid does not act merely as an in situ hydrogen source or hydrogen donor molecule. Actually, is seems to react with lignin through a formylation-elimination-hydrogenolysis mechanism that leads to the depolymerization of the biopolymer. This reaction competes with formic acid decomposition, which gives mainly H2 and CO2 , and forms a complex reaction system. To the best of our knowledge, this is the first time that the distinctive role/mechanism of formic acid has been observed in the conversion of real lignin feedstock. In addition, the solvent, especially ethanol, seems also to play a vital role in the stabilization of the depolymerized monomers and in the elimination/deformylation step.

The Role of the Hydrogen Source on the Selective Production of γ-Valerolactone and 2-Methyltetrahydrofuran from Levulinic Acid.

A mechanistic study of the hydrogenation reaction of levulinic acid (LA) to 2-methyltetrahydrofuyran (MTHF) was performed using three different solvents under reactive H2 and inert N2 atmospheres. Under the applied reaction conditions, catalytic transfer hydrogenation and hydrogenation with molecular H2 were effective at producing high yields of γ-valerolactone. However, the conversion of this stable intermediate to MTHF required the combination of both hydrogen sources (the solvent and the H2 atmosphere) to achieve good yields. The reaction system with 2-propanol as solvent and Ni-Cu/Al2 O3 as catalyst allowed full conversion of LA and a MTHF yield of 80 % after 20 h reaction time at 250 °C and 40 bar of H2 (at room temperature). The system showed the same catalytic activity at LA feed concentrations of 5 and up to 30 wt%, and also when high acetone concentration at the beginning of the reaction were added, which confirmed the potential industrial applications of this solvent/catalyst system.

One-Pot 2-Methyltetrahydrofuran Production from Levulinic Acid in Green Solvents Using Ni-Cu/Al2 O3 Catalysts.

The one-pot hydrogenation of levulinic acid to 2-methyltetrahydrofuran (MTHF) was performed using a series of Ni-Cu/Al2 O3 catalysts in green solvents, such as water and biomass-derived alcohols. Ni/Al2 O3 provided the highest activity, whereas Cu/Al2 O3 was the most selective, reaching a 75 % MTHF yield at 250 °C after 24 h reaction time. Synergetic effects were observed when bimetallic Ni-Cu/Al2 O3 catalysts were used, reaching a 56 % MTHF yield in 5 h at 250 °C for the optimum Ni/Cu ratio. Remarkably, these high yields were obtained using non-noble metal-based catalysts and 2-propanol as the solvent. The catalytic activity and selectivity results are correlated to temperature programmed reduction (TPR), XRD, and STEM characterization data, identifying the role associated with mixed Ni-Cu particles in addition to monometallic Cu and Ni.

Selective oxidation of n-butanol using gold-palladium supported nanoparticles under base-free conditions.

The base-free selective catalytic oxidation of n-butanol by O2 in an aqueous phase has been studied using Au-Pd bimetallic nanoparticles supported on titania. Au-Pd/TiO2 catalysts were prepared by different methods: wet impregnation, physical mixing, deposition-precipitation and sol immobilisation. The sol immobilisation technique, which used polyvinyl alcohol (PVA) as the stabilizing agent, gave the catalyst with the smallest average particle size and the highest stable activity and selectivity towards butyric acid. Increasing the amount of PVA resulted in a decrease in the size of the nanoparticles. However, it also reduced activity by limiting the accessibility of reactants to the active sites. Heating the catalyst to reflux with water at 90 °C for 1 h was the best method to enhance the surface exposure of the nanoparticles without affecting their size, as determined by TEM, X-ray photoelectron spectroscopy and CO chemisorption analysis. This catalyst was not only active and selective towards butyric acid but was also stable under the operating conditions.

Hydrodeoxygenation of the angelica lactone dimer, a cellulose-based feedstock: simple, high-yield synthesis of branched C7 -C10 gasoline-like hydrocarbons.

Dehydration of biomass-derived levulinic acid under solid acid catalysis and treatment of the resulting angelica lactone with catalytic K2 CO3 produces the angelica lactone dimer in excellent yield. This dimer serves as a novel feedstock for hydrodeoxygenation, which proceeds under relatively mild conditions with a combination of oxophilic metal and noble metal catalysts to yield branched C7 -C10 hydrocarbons in the gasoline volatility range. Considering that levulinic acid is available in >80 % conversion from raw biomass, a field-to-tank yield of drop-in, cellulosic gasoline of >60 % is possible.