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The selective oxidation of monosaccharides into sugar acids is an important reaction for the production of biomass-based chemicals, but the design of an efficient catalyst remains a big challenge. Herein we report a series of efficient and stable surface functionalized carbon nanotube supported palladium catalysts for the selective oxidation of monosaccharides into sugar acids at room temperature. The palladium nanoparticles supported on alkaline carbon nanotubes (Pd/CNT-N) showed the highest reaction activity. The maximum gluconic acid yield of 98.3% and xylonic acid yield of 95.8% were obtained at 30 °C within 180 min. DFT calculations revealed that the mechanism of xylose oxidation to xylonic acid involved the activation of OH−, adsorption of xylose, dissociation of the formyl C–H bond in xylose, formation of chemisorbed xylonic acid, and desorption of xylonic acid. The activation energy barrier for xylose oxidation over Pd/CNT-N is lower than that of Pd/CNT-O, explaining that the basic groups on CNT are more beneficial for accelerating monosaccharide oxidation and enhancing the sugar acid selectivity. This work not only presents a new facile route to produce sugar acid at room temperature, but also provides a basis to design and develop efficient catalysts with surface functionalized supports for various catalytic reactions.

The conversion of lignocellulose into a value-added chemical with high selectivity is of great significance but is a big challenge due to the structural diversities of biomass components. Here, we have reported an efficient approach for the one-step conversion of raw lignocellulose into diethyl maleate by the polyoxometalate ionic liquid [BSmim]CuPW12O40 in ethanol under mild conditions. The results reveal that all of the fractions in biomass, i.e., cellulose, lignin and hemicellulose, were simultaneously converted into diethyl maleate (DEM), achieving a 329.6 mg g−1 yield and 70.3% selectivity from corn stalk. Importantly, the performance of the ionic liquid catalyst [BSmim]CuPW12O40 was nearly twice that of CuHPW12O40, which can be attributed to the lower incorporation of the Cu2+ site in [BSmim]CuPW12O40. Hence, this process opens a promising route for producing bio-based bulk chemicals from raw lignocellulose without any pretreatment.

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 β-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.

Lignocellulosic materials were conventionally treated as wastes for disposal, but have now become very important in modern life due to their great roles in the supply of renewable resources. Recently, significant attention has been paid to the dissolution of cellulose, hemicellulose, and lignin, and the production of chemicals and fuels from these feedstocks. It has been demonstrated that lignocellulose has great potential from a sustainable economy perspective and this field has been developing rapidly. Thus, it is critical to review the recent progress in studies on the utilization of lignocellulosic materials. In particular, this work was designed to highlight recent computation-based studies on the chemistry of lignocellulosic materials, from the structural and energetic properties of individual lignocellulose components to their reaction mechanisms in various systems. Importantly, this review summarizes some major simulation studies on the utilization of cellulose, hemicellulose, and lignin via dissolution, catalytic conversion, and pyrolysis by using density functional theory, first-principles calculation, molecular dynamics simulation, and conductor-like screening models. It has been shown that the theoretical and computational investigations play a key role in the understanding of the efficient utilization of lignocellulose.

Lignin selective depolymerization is a crucial step in high-value utilization of this natural aromatic polymer. In this study, we provide a novel and efficient hydrogenolysis process for organosolv lignin selective decomposition and char elimination over non-noble metallic nickel supported on zirconium phosphate (Ni/ZrP). With the optimized catalyst of 15%Ni/ZrP-2.0, 87.3% lignin conversion could be obtained with less than 5.2% char formation under mild condition of 260 °C for 4 h. Product analysis demonstrates that 15.1 wt% phenolic monomer yield is given at the relatively low hydrogen pressure of 2.0 MPa. In particular, 40.4% of these volatile products were identified to be para ethyl phenol (a yield of 6.1 wt%), a versatile compound which is currently originating from the petrochemical industry. Further comparative structure characterization of the original and regenerated lignin shows that the efficient cleavage of carbon bonds between C8 and C9 in the p-coumarate moiety of H-lignin (pCA8 unit) is mainly responsible for this excellent yield of para ethyl phenol. In addition, this process yields 48 wt% nonvolatile products, which mainly consist of phenolic dimers and trimers, indicating its great potential to be a good starting material for high quality aromatic fuel production via simple upgradation techniques.

Selective oxidation of biomass-based monosaccharides into value-added sugar acids is highly desired, but limited success of producing D-xylonic acid has been achieved. Herein, we report an efficient catalyst system, viz., Au nanoparticles anchored on the inner walls of hollow Al2O3 nanospheres (Au@h-Al2O3), which could catalyze the selective oxidation of D-xylose into D-xylonic acid under base-free conditions. The mesoporous Al2O3 shell as the adsorbent first adsorbed D-xylose. Then, the interface of Au nanoparticles and Al2O3 as active sites spontaneously dissociated O2, and the exposed Au nanoparticle surface as the catalytic site drove the transformation. With this catalyst system, the valuable D-xylonic acid was produced with excellent yields in the aerobic oxidation of D-xylose. Extensive investigation showed that Au@h-Al2O3 is an efficient catalyst with high stability and recyclability.

Selective valorization of lignin to achieve high value and commodity chemicals is attracting increasing attention. In this work, an efficient and reusable metal-based ionic liquid (MBIL) was developed for the selective tailoring of p-coumaric acid ester (pCA), a typical p-hydroxyphenyl (H) unit, into methyl p-hydroxycinnamate (MPC). Under optimized conditions and in the presence of catalyst [Bmim][FeCl4], a volatile aromatic product of 10.5 wt% was obtained, of which, 70.5% separated as pure MPC with an isolated yield of 71.1 mg g−1. FT-IR, 13C NMR, ANO and 2D HSQC demonstrated that the H unit was preferentially tailored from lignin, of which, 86.0 wt% of the H structure unit is cut off from lignin, with 70.6% being selectively converted to MPC. Further investigation demonstrated that MBIL prefers to tailor ester bonds compared to ether bonds using model compounds, and the superior catalytic ester bond cleavage performance exhibited by [Bmim][FeCl4] can be ascribed to the relatively narrow energy gap between the lignin ester bond and [FeCl4]− anion and to the comparatively low absolute binding energy between the cation and anion through DFT calculations.

Catalytic transformation of readily available widely distributed and renewable non-food lignocelluloses to value-added chemicals has been recognized as an efficient approach for the alleviation of the increasing energy crisis and climate change. An efficient catalytic transformation process for agricultural residual lignocelluloses in cooperative ionic liquid pairs was achieved. The promotion of the dissolution equilibrium, combined with rapid, in situ acid-catalyzed degradation of cellulose and hemicellulose, resulted in significantly greater conversion of the biomass to biochemicals and selective delignification through further comparative analyses of the raw materials, products and residues by GC-MS, GPC, FT-IR, SEM and elemental characterization.

A 100% conversion of cellulose to industrially useful chemicals is, for the first time, achieved in a single pot reaction by the use of cooperative ionic liquid pairs for combined dissolution and catalytic degradation of cellulose, which overcomes the long intrinsic phase problem in the conversion of biomass to chemicals. © 2011 The Royal Society of Chemistry.