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

Discovery of a Highly Active Catalyst for Hydrogenolysis of C-O Bonds via Systematic, Multi-metallic Catalyst Screening

Hydrogenolysis of C-O bonds is a highly challenging reaction with the most efficient catalysts based on bimetallic assemblies. Systematic studies to identify the optimum metal combination have not been performed and, therefore, we designed a method to screen multi-metallic catalysts, including all water stable transition metals, using diphenyl ether as a model substrate. Bimetallic Pd-Pt (70 : 30) nanoparticles were the most efficient, catalyzing the hydrogenolysis of the C-O bond in diphenyl ether at 95 degrees C and 1 atm of hydrogen in quantitative yield. This research provides insights into the activity of multi-metallic catalysts in hydrogenolysis reactions. The catalyst was successfully applied in the reductive fractionation of bio-mass affording key products in near-quantitative yields

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-polyelectrolytebased 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

Synthesis of Cross-linked Ionic Poly(styrenes) and their Application as Catalysts for the Synthesis of Carbonates from CO2 and Epoxides

A series of dicationic styrene-functionalized imidazolium-based salts, in which the two imidazolium rings are bridged by a functionalized spacer, are prepared. The salts are polymerized to afford cross-linked imidazolium-based ionic polystyrene materials, which, owing to the presence of the functionalized spaces, should be highly active organocatalysts for the cycloaddition of CO2 to epoxides to afford cyclic carbonates (CCE reaction). The catalytic activities of the polymers are evaluated in the CCE reaction. The most active catalyst incorporates a diol functionality and is active at 80 degrees C and a pressure of 4bar at a loading of 5mol%, which is comparable to the most active organocatalysts. Moreover, high yields can be obtained under atmospheric pressure upon increasing the temperature to 120 degrees C. Under harsher conditions, the catalyst is highly active at a loading one order of magnitude lower, highlighting the importance of benchmark conditions for the CCE reaction. Moreover, the polymer catalysts are advantageous because they can be used at low catalyst loadings, the carbonate product is easily isolated in pure form, and loss of activity of the recovered polymer catalyst is not observed during reuse

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

[Image: see text] 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

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

Oxidative cleavage of -O-4 bonds in lignin model compounds with a single-atom Co catalyst

Single-atom catalysts are emerging as primary catalysts for many reactions due to their 100% utilization of active metal centers leading to high catalytic efficiencies. Herein, we report the use of a single-atom Co catalyst for the oxidative cleavage of the -O-4 bonds of lignin model compounds at a low oxygen pressure. Under the optimized reaction conditions, the conversion of 2-(2-methoxyphenoxy)-1-phenylethanol up to 95% with high selectivities was achieved with a variety of substrates investigated. The reusability of the Co catalyst with a high catalytic efficiency indicates its potential application in the oxidative cleavage of C-O bonds

Anchoring single platinum atoms onto nickel nanoparticles affords highly selective catalysts for lignin conversion

Due to the highly complex polyphenolic structure of lignin, depolymerization without a prior chemical treatment is challenging, and new catalysts are required. Atomically dispersed catalysts are able to maximize the atomic efficiency of noble metals, simultaneously providing an alternative strategy to tune the activity and selectivity by alloying with other abundant metal supports. Here, we report a highly active and selective catalyst comprising monodispersed (single) Pt atoms on Ni nanoparticles supported on carbon (denoted as Pt1Ni/C, where Pt-1 represents single Pt atoms), designed for the reductive depolymerization of lignin. Selectivity toward 4-n-propylsyringol and 4-n-propylguaiacol exceeds 90%. The activity and selectivity of the Pt1Ni/C catalyst in the reductive depolymerization of lignin may be attributed to synergistic effects between the Ni nanoparticles and the single Pt atoms