Towards the upgrading of fermentation broths to advanced biofuels: a water tolerant catalyst for the conversion of ethanol to isobutanol

The conversion of methanol/ethanol mixtures to isobutanol with the pre-catalyst trans-[RuCl2(dppm)2] (1) is tolerant to the addition of water to the system, achieving an isobutanol yield of 36% at 78% selectivity with water concentrations typical of that of a crude fermentation broth.</p

Robust synthesis of epoxy resin-filled microcapsules for application to self-healing materials

Mechanically and thermally robust microcapsules containing diglycidyl ether bisphenol A-based epoxy resin and a high-boiling-point organic solvent were synthesized in high yield using in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. Microcapsules were characterized in terms of their size and size distribution, shell surface morphology and thermal resistance to the curing cycles of commercially used epoxy polymers. The size distribution of the capsules and characteristics such as shell thickness can be controlled by the specific parameters of microencapsulation, including concentrations of reagents, stirrer speed and sonication. Selected microcapsules, and separated core and shell materials, were analysed using thermogravimetric analysis and differential scanning calorimetry. It is demonstrated that capsules lose minimal 2.5 wt% at temperatures no higher than 120°C. These microcapsules can be applied to self-healing carbon fibre composite structural materials, with preliminary results showing promising performance

Homogeneous Ethanol to Butanol Catalysis - Guerbet Renewed

The catalytic conversion of (bio)ethanol into butanol is an attractive route to upgrade the modest fuel characteristics of this widely available bioderived substrate into a molecule that has properties much closer to conventional gasoline. The Guerbet reaction, known for more than 100 years, provides an ideal mechanism for this transformation. However, despite the apparently simple nature of this reaction for ethanol, it provides formidable challenges, especially in terms of achieving high selectivity. There have been advances in both heterogeneous and homogeneous catalysis in this regard, and this Perspective focuses on the very recent reports of homogeneous catalysts that describe encouraging results in terms of achieving high selectivity, mechanistic understanding, and widening scope

Thermally induced reversible and reprogrammable actuation of tough hydrogels utilising ionoprinting and iron coordination chemistry

Ionoprinting has proven itself as a technique capable of enabling repeated post-synthesis programming of hydrogels into a variety of different shapes, achieved through a variety of different actuation pathways. To date, the technique of ionoprinting has been limited to conventional brittle hydrogels, with reversible actuation requiring a change in submersion solution. In this study, ionoprinting has been combined for the first time with a tougher interpenetrating network polymer (IPN) hydrogel with dual pH and temperature responsiveness. This new methodology eliminates the brittle material failure typically occurring during shape change programming and actuation in hydrogels, thus allowing for the realisation of more highly strained and complex shape formation than previously demonstrated. Critically, the temperature responsiveness of this system enables actuation between an unfolded (2D) and a folded (3D) shape through an external stimuli; enabling reversible actuation without a change in submersion solution. Here, the reversible thermally induced actuation is demonstrated for the first time through the formation of complex multi-folded architectures, including an origami crane bird and Miura folds, from flat hydrogel sheets. The robustness of the IPN hydrogel is demonstrated through multiple reprogramming cycles and repeated actuation of a single hydrogel sheet formed into 3D shapes (hexagon, helix and zig-zag). These advancements vastly improve the applicability of ionoprinting extending its application into areas of soft robotics, biomedical engineering and enviro intelligent sensors

Rhenium Complexes Bearing Tridentate and Bidentate Phosphinoamine Ligands in the Production of Biofuel Alcohols via the Guerbet Reaction

We report a variety of rhenium complexes supported by bidentate and tridentate phosphinoamine ligands and their use in the formation of the advanced biofuel isobutanol from methanol and ethanol. Rhenium pincer complexes 1–3 are effective catalysts for this process, with 2 giving isobutanol in 35% yields, with 97% selectivity in the liquid fraction, over 16 h with catalyst loadings as low as 0.07 mol %. However, these catalysts show poorer overall selectivity, with the formation of a significant amount of carboxylate salt solid byproduct also being observed. Production of the active catalyst 1d has been followed by 31P NMR spectroscopy, and the importance of the presence of base and elevated temperatures to catalyst activation has been established. Complexes supported by diphosphine ligands are inactive for Guerbet chemistry; however, complexes supported by bidentate phosphinoamine ligands show greater selectivity for isobutanol formation over carboxylate salts. The novel complex 7 was able to produce isobutanol in 28% yield over 17 h. The importance of the N–H moiety to the catalytic performance has also been established, giving further weight to the hypothesis that these catalysts operate via a cooperative mechanism

Cooperative Lewis pairs based on late transition metals: activation of small molecules by platinum(0) and B(C6F5)3

A Lewis basic platinum(0)–CO complex supported by a diphosphine ligand and B(C6F5)3 act cooperatively, in a manner reminiscent of a frustrated Lewis pair, to activate small molecules such as hydrogen, CO2, and ethene. This cooperative Lewis pair facilitates the coupling of CO and ethene in a new way

Optimisation of epoxy blends for use in extrinsic self-healing fibre-reinforced composites

AbstractA range of epoxy blends were investigated to determine their mechanical properties and suitability for use as healing agents for the repair of fibre-reinforced polymer (FRP) composites. Key requirements for an effective healing agent are low viscosity, and good mechanical performance. A base epoxy resin was selected and blended with a variety of diluents and a toughening agent, and the physical and mechanical properties of the resulting polymers were investigated. Single lap shear strengths of up to 139% of the base epoxy values were demonstrated, while double cantilever beam testing showed specimens healed with optimised epoxy blends can provide recoveries in fracture toughness of up to 269%, compared to 56% in specimens healed with the base epoxy resin. Cross-ply FRP laminate tensile specimens were used to highlight the potential to recover stiffness decay caused by intraply cracking. Following infusion of the damage via embedded vascules, the toughened epoxies were capable of providing complete recovery of stiffness

Transition metal cooperative Lewis pairs using platinum(0) piphosphine Mmonocarbonyl complexes as Lewis bases

The platinum(0)-diphosphine complex [Pt(CO)(L1)] (3, where L1 = 1,2-C6H4(CH2PtBu2)2) and its diphosphinite analogue [Pt(CO)(L2)] (11, where L2 = 1,2-C6H4(OPtBu2)2) act as Lewis bases in conjunction with the main group Lewis acid B(C6F5)3 to form frustrated or cooperative Lewis pairs. These systems activate dihydrogen, ethene/carbon monoxide, and phenylacetylene, leading to products that depend on the exact ligand used. These subtle changes to ligand structure influence reactivity, most notably in hydrogen activation where a variety of dinuclear species of the type [(diphos)Pt(μ-H)3Pt(diphos)]+ or [(diphos)Pt(μ-H)(μ-CO)Pt(diphos)]+ are observed. Activation of ethene with the Lewis pair leads to a previously reported coupling product and the mechanism is probed. The basicity of [Pt(CO)(L)] is demonstrated by deprotonation of phenylacetylene. Preliminary studies with an analogous palladium complex [Pd(CO)(L1)] 33 suggests related chemistry may be exploited for this metal. These results provide further examples of cooperative Lewis pair behavior in which one of the components is based on a transition metal complex

Radical-initiated P,P-metathesis reactions of diphosphanes: evidence from experimental and computational studies

By combining the diphosphanes Ar2P–PAr2, where Ar = C6H5, 4-C6H4Me, 4-C6H4OMe, 3,5-C6H3(CF3)2, it has been shown that P,P-metathesis generally occurs rapidly under ambient conditions. DFT calculations have shown that the stability of unsymmetrical diphosphanes Z2P–PZ′2 is a function of the difference between the Z and Z′ substituents in terms of size and electronegativity. Of the mechanisms that were calculated for the P,P-metathesis, the most likely was considered to be one involving Ar2P˙ radicals. The observations that photolysis increases the rate of the P,P-metatheses and TEMPO inhibits it, are consistent with a radical chain process. The P,P-metathesis reactions that involve (o-Tol)2P–P(o-Tol)2 are anomalously slow and, in the absence of photolysis, were only observed to take place in CHCl3 and CH2Cl2. The role of the chlorinated solvent is ascribed to the formation of Ar2PCl which catalyses the P,P-metathesis. The slow kinetics observed with (o-Tol)2P–P(o-Tol)2 is tentatively attributed to the o-CH3 groups quenching the (o-Tol)2P˙ radicals or inhibiting the metathesis reaction sterically

Manganese diphosphine and phosphinoamine complexes are effective catalysts for the production of biofuel alcohols via the Guerbet reaction

We report a variety of manganese-based catalysts containing both chelating diphosphine (bis(diphenylphosphino)methane (dppm: 1, 2, and 7) or 1,2-bis(diphenylphosphino)ethane (dppe: 3)), and mixed-donor phosphinoamine (2-(diphenylphosphino)ethylamine (dppea: 4–6)) ligands for the upgrading of ethanol and methanol to the advanced biofuel isobutanol. These catalysts show moderate selectivity up to 74% along with turnover numbers greater than 100 over 90 h, with catalyst 2 supported by dppm demonstrating superior performance. The positive effect of substituting the ligand backbone was also displayed with a catalyst supported by C-phenyl-substituted dppm (8) having markedly improved performance compared to the parent dppm catalysts. Catalysts supported by the phosphinoamine ligand dppea are also active for the upgrading of ethanol to n-butanol. These results show that so-called PNP-pincer ligands are not a prerequisite for the use of manganese catalysts in Guerbet chemistry and that simple chelates can be used effectively