Lignin First: Confirming the Role of the Metal Catalyst in Reductive Fractionation

Rhodium nanoparticles embedded on the interior of hollow porous carbon nanospheres, able to sieve monomers from polymers, were used to confirm the precise role of metal catalysts in the reductive catalytic fractionation of lignin. The study provides clear evidence that the primary function of the metal catalyst is to hydrogenate monomeric lignin fragments into more stable forms following a solvent-based fractionation and fragmentation of lignin.

Utility of Core-Shell Nanomaterials in the Catalytic Transformations of Renewable Substrates

In recent years, core-shell nano-catalysts have received increasing attention due to their tunable properties and broad applications in catalysis. Control of the two components of these materials allows their catalytic properties to be tuned to various sustainable processes in synthetic and energy-related applications. This Concept article describes recent state-of-the-art core-shell materials and their application as heterogeneous catalysts for a range of sustainable catalytic transformations, focusing on two important classes of renewable substrates, CO₂ and biomass. In the discussion, emphasis is directed to the role of the constituent parts of the core-shell structure and how they can be manipulated to enhance activity.

Acceptorless dehydrogenation and hydrogenation of N- and O-containing compounds on Pd3Au1(111) facets

Catalytic dehydrogenation and hydrogenation of amines and alcohols are important in the synthesis of fine chemicals. Despite several efficient homogeneous catalysts having been identified, highly active heterogeneous catalysts remain elusive, although they would meet an unmet need. Here, we show that bimetallic Pd-Au nanoparticles with Pd-to-Au molar ratios of 3:1 immobilized on multiwall carbon nanotubes (Pd3Au1/CNT) display high catalytic activity in the oxidant-free and acceptorless dehydrogenation and hydrogenation of N- and O-containing heterocyclic compounds, amines/imines, and alcohols/ketones. Transmission electron microscopy analysis demonstrates the preferential exposure of Pd3Au1(111) facets on the Pd3Au1/CNT catalyst. Mechanistic insights combining experimental data with density functional theory calculations reveal that the Pd3Au1(111) surface enhances both dehydrogenation and hydrogenation reactions and provides a rationale for the observed enhancements.

Sustainable, Reshapable Surfactant-Polyelectrolyte Plastics Employing Water as a Plasticizer

Natural polymers such as those present in foods contain abundant noncovalent intra- and intermolecular interactions, notably hydrogen bonds, which make them rigid when dry, but on exposure to water soften, due to disruption of these interactions. This softening process allows them to be reshaped. Food-derived materials, however, have limited practical use due to their high brittleness and gradual degradation. Nevertheless, inspired by such properties, surfactant-polyelectrolyte-based polymers that contain abundant ionic interactions and can be repeatedly reshaped using water as plasticizer are described. The polymers, on the basis of main chain anionic poly(styrene sulfonates) combined with phosphonium surfactant, are readily synthesized with well-defined lamellar domains through interfacial metathesis reactions. The polymers present typical stress-strain characteristics of plastics, and their modulus undergoes a decrease of ca. 3 orders of magnitude upon shear and stretch forces after plasticizing with water. Since recycling of plastics generally involves complicated and energy-intensive processes (that leads to the majority of plastics being land-filled or incinerated), it is envisaged that reshapable polymers, such as those described here, could reduce the amount of plastic waste as they can be remolded as and when required, thus reducing pollution and the depletion of resources, ultimately contributing to a more sustainable society.

Metal-Sulfide Catalysts Derived from Lignosulfonate and their Efficient Use in Hydrogenolysis

Catalytic lignosulfonate valorization is hampered by the in situ liberation of sulfur that ultimately poisons the catalyst. To overcome this limitation, metal sulfide catalysts were developed that are able to cleave the C-O bonds of lignosulfonate and are resistant to sulfur poisoning. The catalysts were prepared by using the lignosulfonate substrate as a precursor to form well-dispersed carbon-supported metal (Co, Ni, Mo, CoMo, NiMo) sulfide catalysts. Following optimization of the reaction conditions employing a model substrate, the catalysts were used to generate guaiacyl monomers from lignosulfonate. The Co catalyst was able to produce 23.7 mg of 4-propylguaiacol per gram of lignosulfonate with a selectivity of 84 %. The catalysts operated in water and could be recycled and reused multiple times. Thus, it was demonstrated that an inexpensive, sulfur-tolerant catalyst based on an earth-abundant metal and lignosulfonate efficiently catalyzed the selective hydrogenolysis of lignosulfonate in water in the absence of additives.

Indirect CO2 Methanation: Hydrogenolysis of Cyclic Carbonates Catalyzed by Ru-Modified Zeolite Produces Methane and Diols

We report a ruthenium-modified zeolite which efficiently transforms propylene carbonate to propylene glycol and methane, under solvent-free conditions. The catalyst achieved high product selectivity and no significant ageing effect was observed after multiple cycles. The resulting liquid product (water-containing glycol) can be directly used as anti-freeze solution and the gas phase can directly be used as an energy carrier in the form of H₂ -enriched methane. This process efficiently bridges energy storage and an important chemical synthesis under sustainable (CO₂ consuming) conditions.

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

The strategies and challenges in the preparation of fully renewable materials prepared from CO₂ and biomass enabled by catalysis are presented.

Efficient cleavage of aryl ether C-O linkages by Rh-Ni and Ru-Ni nanoscale catalysts operating in water

Rh–Ni and Ru–Ni nanocatalysts efficiently catalyze the hydrogenolysis of C–O bonds under mild operating conditions in water.

Bimetallic Ru–Ni and Rh–Ni nanocatalysts coated with a phase transfer agent efficiently cleave aryl ether C–O linkages in water in the presence of hydrogen. For dimeric substrates with weaker C–O linkages, i.e. α-O-4 and β-O-4 bonds, low loadings of the precious metal (Rh or Ru) in the nanocatalysts quantitatively afford monomers, whereas for the stronger 4-O-5 linkage higher amounts of the precious metal are required to achieve complete conversion. Under the optimized, relatively mild operating conditions, the C–O bonds in a range of substituted ether compounds are efficiently cleaved, and mechanistic insights into the reaction pathways are provided. This work paves the way to sustainable approaches for the hydrogenolysis of C–O bonds.