Cleavage of aromatic ether bonds through hydrogenolysis is one of the most promising routes for depolymerisation and transformation of lignin into value-added chemicals. Instead of using pressurized ...hydrogen gas as hydrogen source, some reductive organic molecules, such as methanol, ethanol, isopropanol as well as formates and formic acid, can serve as hydrogen donor is the process called catalytic transfer hydrogenolysis. This is an emerging and promising research field but there are very few reports. In this paper, a comprehensive review of the works is presented on catalytic transfer hydrogenolysis of lignin and lignin model compounds aiming to breakdown the aromatic ethers including α-O-4, β-O-4 and 4-O-5 linkages, with focus on reaction mechanisms. The works are organised regarding to different hydrogen donors used, to gain an in-depth understanding of the special role of various hydrogen donors in this process. Perspectives on current challenges and opportunities of future research to develop catalytic transfer hydrogenolysis as a competitive and unique strategy for lignin valorisation are also provided.
Catalytic transfer hydrogenolysis offers a new promising pathway to lignin cleavage. The up-to-date contributions in this emerging research field is reviewed to get an in-depth understanding of the unique mechanisms. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In coordination chemistry, catalytically active metal complexes in a zero‐ or low‐valent state often adopt four‐coordinate square‐planar or tetrahedral geometry. By applying this principle, we have ...developed a stable Pt1 single‐atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)‐modified active carbon. This was achieved by anchoring Pt on the four‐fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square‐planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.
An atomically dispersed Pt1 catalyst has been developed with a high catalyst loading where each Pt atom is anchored on supported phosphomolybdic acid with distorted square‐planar coordination geometry. The catalyst is highly active for nitrobenzene and cyclohexanone hydrogenation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we ...report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al
2
O
3
, likely stabilized by coordinatively unsaturated pentahedral Al
3+
centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al
2
O
3
and control samples, this system exhibits significantly enhanced stability and performance for
n
-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period.
Production of renewable chemicals with established market and high value is highly desirable in biomass utilization. Herein, glucosamine, an amino sugar with various applications, was generated in a ...single step by the acid‐catalyzed transformation of chitin. Aprotic polar solvents were mixed with water to promote the hydrolysis as well as the deacetylation reactions, significantly enhancing product yield and/or reducing the concentration and amount of acid catalyst required. By employing the optimized co‐solvent system, glucosamine was achieved with 80 % yield at 175 °C in 1 h from ball‐milled chitin, in sharp contrast with the pure water system with the same acid concentration in which less than 1 % glucosamine was obtained. Correlations between the promotional effect and various solvent property parameters were discussed and proposed, providing guidance on the choice of solvent for further optimization of the co‐solvent system for similar applications.
Food additives from chitin: Glucosamine, an amino sugar with various applications in medicine, nutritional supplements, food and beverages, was generated in high yield by co‐solvent promoted, acid‐catalyzed transformation of chitin in a one‐step procedure. The optimized gave glucosamine in 80 % yield at 175 °C in 1 h from ball‐milled chitin, in sharp contrast with the pure water system with the same acid concentration in which less than 1 % glucosamine was obtained.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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•EP particles as a novel bacteria carrier on crack-healing in concrete was studied.•EP particles exert more positive effects on the healing capacity over EC particles.•Microstructures ...of the mineral precipitations on the crack surface were analyzed.•Completely healed crack widths were maximized in EP-B specimens.
Immobilization has been reported to be an efficient approach for bacteria-based self-healing concrete to maintain the high-efficiency mineral-forming capacity of incorporated bacteria over a period of time. However, the relatively high-cost, local unavailability, and low adsorption capacity of the current bacteria carriers make them impractical for potential implementation in large-scale concrete structures. In this study, the feasibility of expanded perlite (EP) as a novel bacteria carrier on quantifying cracks-healing in concrete via immobilization of Bacillus cohnii was demonstrated. The effects of two other self-healing techniques, i.e., direct introduction of bacteria and expanded clay (EC) immobilized bacteria, on the efficiency of crack-healing were also investigated. Experimental results showed that specimens incorporated with EP-immobilized bacteria exhibited the most efficient crack-healing after each healing time. The values of completely healed crack widths were up to 0.79mm after 28days of healing, which is larger than the value of 0.45mm for specimens incorporated with EC-immobilized bacteria. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) analysis confirmed that mineral precipitations on their crack surfaces are calcite crystals. The findings obtained in this study may provide a scientific basis for the potential implementation of expanded perlite, as a new microorganism carrier, in bacteria-based self-healing concrete.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Research on single‐atom catalysts (SACs), or atomically dispersed catalysts, has been quickly gaining momentum over the past few years. Although the unique electronic structure of singly dispersed ...atoms enables uncommon—sometimes exceptional—activities and selectivities for various catalytic applications, developing reliable and general procedures for preparing stable, active SACs in particular for applications under reductive conditions remains a major issue. Herein, the challenges associated with the synthesis of SACs are highlighted semiquantitatively and three stabilization techniques inspired by colloidal science including steric, ligand, and electrostatic stabilization are proposed. Some recent examples are discussed in detail to showcase the power of these strategies in the synthesis of stable SACs without compromising catalytic activity. The substantial further potential of steric, ligand, and electrostatic effects for developing SACs is emphasized. A perspective is given to point out opportunities and remaining obstacles, with special attention given to electrostatic stabilization where little is done so far. The stabilization strategies presented herein have a wide applicability in the synthesis of a series of new SACs with improved performances.
Conventional knowledge from colloidal science can be employed to stabilize isolated metal atoms for catalytic applications. Critical challenges in the field of single‐atom catalysis alongside recent advances in developing strategies to overcome stability issues and future directions are showcased and discussed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this paper, NiRu, NiRh, and NiPd catalysts were synthesized and evaluated in the hydrogenolysis of lignin C–O bonds, which is proved to be superior over single-component catalysts. The optimized ...NiRu catalyst contains 85% Ni and 15% Ru, composed of Ni surface-enriched, Ru–Ni atomically mixed, ultrasmall nanoparticles. The Ni85Ru15 catalyst showed high activity under low temperature (100 °C), low H2 pressure (1 bar) in β-O-4 type C–O bond hydrogenolysis. It also exhibited significantly higher activity over Ni and Ru catalysts in the direct conversion of lignin into monomeric aromatic chemicals. Mechanistic investigation indicates that the synergistic effect of NiRu can be attributed to three factors: (1) increased fraction of surface atoms (compared with Ni), (2) enhanced H2 and substrate activation (compared with Ni), and (3) inhibited benzene ring hydrogenation (compared with Ru). Similarly, NiRh and NiPd catalysts were more active and selective than their single-component counterparts in the hydrogenolysis of lignin model compounds and real lignin.
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IJS, KILJ, NUK, PNG, UL, UM
Protective ligands are key components of ligand‐protected metal nanoclusters (NCs), as they offer good stability and multiple functionalities to the metal NCs in solution. Herein, we demonstrated ...that the ligand landscape on the NC surface could also be used to modulate the catalytic active sites of metal NCs in solution thus to direct the catalytic reaction towards desirable products through a different pathway. We found that thiolate ligands, namely, p‐mercaptobenzoic acid (p‐MBA), in Au25(p‐MBA)18 NCs could influence the reaction pathway in the catalytic hydrogenation of 4‐nitrophenol in solution. In particular, the well‐defined ligand structure of Au25(p‐MBA)18 NCs in solution provided a unique environment for the coadsorption of two substrate molecules (4‐nitrophenol) on the Au NC surface, and this ligand modulation could activate a reaction pathway involving the formation of azobenzene intermediates from the two adsorbed substrate molecules, which are missing in nanogold catalysts without protective ligands. The discovery of this alternative reaction pathway highlights the importance of ligands on nanogold catalysts in modulating their active sites and directing their catalytic reaction pathways in solution and provides good opportunities to tailor the selectivity of ligand‐protected metal NC catalysts.
The road less traveled: We demonstrate that the ligand landscape on a nanocluster (NC) surface can be used to modulate the catalytic active sites of metal NCs in solution thus to direct the reaction towards desirable products through a pathway different from that commonly reported. We highlight the importance of ligands on nanogold catalysts to tailor the active site exposure and selectivity of ligand‐protected metal NC catalysts.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper describes chitin liquefaction in ethylene glycol (EG) under the catalysis of sulfuric acid for the first time. Up to 75% of chitin was liquefied at 165 °C within 90 min by using 8 wt % of ...acid (refer to the mass of EG). The major products (30% yield) were identified to be hydroxyethyl-2-amino-2-deoxyhexopyranoside (HADP) and hydroxyethyl-2-acetamido-2-deoxyhexopyranoside (HAADP) by GC-MS and confirmed by NMR. Kinetic studies were conducted based on which a plausible mechanism for product formation was proposed. HADP was dominant during the reaction, whereas HAADP formed fast at an initial stage and then most of it was hydrolyzed to HADP. Unreacted chitin residues with different reaction times were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and solid state NMR. The FTIR results showed that negligible deacetylation reaction occurred, supporting the assumption that HADP was produced from the hydrolysis of HAADP rather than directly from chitin polymer chains. The XRD analysis revealed the gradual decrease in crystallinity with the increase in reaction time, indicating the damage of the crystalline domain by the liquefaction process. The simple, cheap, and efficient liquefaction of chitin opens up a new route to produce chemicals and materials from waste in the fishing industry.
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IJS, KILJ, NUK, PNG, UL, UM
10.
Formic acid-mediated liquefaction of chitin Zhang, Jiaguang; Yan, Ning
Green chemistry : an international journal and green chemistry resource : GC,
01/2016, Volume:
18, Issue:
18
Journal Article
Peer reviewed
We report pure formic acid-mediated liquefaction of chitin for the first time. Formic acid exhibited a remarkable ability in the functionalization and depolymerization of ball-milled chitin as well ...as proto-chitin in raw shrimp shells. Up to 60% combined yield of a series of structurally identified monomeric products was obtained after reaction at 100 degree C for 12 h. The product stream could also converge to a single compound, 5-(formyloxymethyl)furfural (FMF), in 35% yield after a longer reaction time. The product evolution was monitored by electrospray ionization mass spectrometry (ESI-MS), and the key finding is that the liquefaction involves several major chemical events in the following sequence: (1) the process starts with partial formylation of the hydroxyl groups in chitin side chains generating soluble polymeric derivatives; (2) formic acid catalyzes polymer chain breakage in a non-conventional, non-hydrolytic pathway forming dehydrated monomers and oligomers; (3) as formylation continues, water accumulates in the system, which induces more monomer and oligomer generation via hydrolysis, and the formation of rehydrated products. As such, water is constantly generated via formylation and subsequently consumed in hydrolysis and rehydration, making the process a self-sustained one.
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