Highly Efficient Hydrogenation of Levulinic Acid into γ-Valerolactone using an Iron Pincer Complex

Homogeneous Catalyzed Direct Conversion of Furfural to Gamma-Valerolactone

Herein, we report the direct conversion of biomass-derived furfural to γ-valerolactone (GVL) in a one-pot system, using the combination of Ru-MACHO-BH and a Brønsted acid (H3PO4). A GVL yield of 84 % is achieved under mild reaction conditions using 1 mol% of Ru-MACHO-BH and 3.8 M H3PO4(aq) at 100 °C for 7 hours.

Metal-Ligand Cooperativity in Iron Dinitrogen Complexes: Proton-Coupled Electron Transfer Disproportionation and an Anionic Fe(0)N2 Hydride

Metal-ligand cooperativity and redox-active ligands enable the use of open-shell first-row transition metals in catalysis. However, the fleeting nature of the reactive intermediates prevents direct inspection of the relevant catalytic species. By employing phosphine α-iminopyridine (PNN)-based complexes, we show that chemical and redox metal-ligand cooperativity can be combined in the coordination sphere of iron dinitrogen complexes. These systems show dual activation modes either through deprotonation, which triggers reversible core dearomatization, or through reversibly accepting one electron by reducing the imine functionality. (PNN)Fe(N₂) fragments can be obtained under mildly reducing conditions. Deprotonation of such complexes induces dearomatization of the pyridine core while retaining a terminally coordinated N₂ ligand. This species is nevertheless stable in solution only below -30 °C and undergoes unusual ligand-assisted redox disproportionation through proton-coupled electron transfer at room temperature. The origin of this phenomenon is the significant lability of the α-imine C-H bonds in the dearomatized species, where the calculated bond dissociation free energy is 48.7 kcal mol^-1. The dispropotionation reaction yields an overreduced iron compound, demonstrating that the formation of such species can be triggered by mild bases, and does not require harsh reducing agents. Reaction of the dearomatized species with dihydrogen yields a rare anionic Fe hydride that binds dinitrogen and features a rearomatized core.

Earth-abundant 3d-transition-metal catalysts for lignocellulosic biomass conversion

Transformation of biomass to chemicals and fuels is a long-term goal in both science and industry. However, high cost is one of the major obstacles to the industrialization of this sustainable technology. Thus, developing catalysts with high activity and low-cost is of great importance for biomass conversion. The last two decades have witnessed the increasing achievement of the use of earth-abundant 3d-transition-metals in catalysis due to their low-cost, high efficiency and excellent stability. Here, we aim to review the fast development and recent advances of 3d-metal-based catalysts including Cu, Fe, Co, Ni and Mn in lignocellulosic biomass conversion. Moreover, present research trends and invigorating perspectives on future development are given.

Hydrogenative Cyclization of Levulinic Acid to γ-Valerolactone with Methanol and Ni-Fe Bimetallic Catalysts

A series of Ni-Fe/SBA-15 catalysts was prepared and tested for the catalytic hydrogenation of levulinic acid to γ-valerolactone, adopting methanol as the only hydrogen donor, and investigating the synergism between Fe and Ni, both supported on SBA-15, towards this reaction. The characterization of the synthesized catalysts was carried out by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), H2-TPD (hydrogen temperature-programmed desorption), XPS (X-ray photoelectron spectroscopy), and in situ FT-IR (Fourier transform–infrared spectroscopy) techniques. H2-TPD and XPS results have shown that electron transfer occurs from Fe to Ni, which is helpful both for the activation of the C=O bond and for the dissociative activation of H2 molecules, also in agreement with the results of the in situ FT-IR spectroscopy. The effect of temperature and reaction time on γ-valerolactone production was also investigated, identifying the best reaction conditions at 200 °C and 180 min, allowing for the complete conversion of levulinic acid and the complete selectivity to γ-valerolactone. Moreover, methanol was identified as an efficient hydrogen donor, if used in combination with the Ni-Fe/SBA-15 catalyst. The obtained results are promising, especially if compared with those obtained with the traditional and more expensive molecular hydrogen and noble-based catalysts.

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.

Surface engineering in PbS via partial oxidation: towards an advanced electrocatalyst for reduction of levulinic acid to γ-valerolactone

Development of mild and efficient strategies for biomass conversion is of great significance, and design of advanced catalysts is crucial for biomass valorization. Herein, we designed PbS-based electrocatalysts through a surface engineering strategy via partial oxidation, and the degree of surface oxidation of PbS to PbSO₄ could be easily tuned by calcination temperature. It was discovered that the prepared electrocatalysts could efficiently catalyze reduction of biomass-derived levulinic acid (LA) to γ-valerolactone (GVL) using water as the hydrogen source. Especially, the electrocatalyst calcined at 400 °C (PbS-400) showed outstanding performance with a current density of 13.5 mA cm^-2 and a GVL faradaic efficiency of 78.6%, which was far higher than the best results reported up to date. Moreover, GVL was the only product from LA reduction, indicating the excellent selectivity. Mechanism investigation showed that LA was converted through electrocatalytic hydrogenation of carbonyl groups of LA and subsequent intramolecular esterification.

Towards practical earth abundant reduction catalysis: design of improved catalysts for manganese catalysed hydrogenation

Rational design using kinetic studies has led to a 3-fold-increase in the reaction-rates compared to an already-promising lead catalyst for the reduction of ketones and esters.