Upgrading of Crude Duckweed Bio-Oil in Subcritical Water

In the present work, crude bio-oil derived from the hydrothermal liquefaction (HTL) of duckweed (<i>Lemna sp.</i>) was treated in subcritical water at different reaction environment (H₂,CO), temperature (330–370 °C), time (2,4 h), and Pt/C sulfide (Pt/C–S) catalyst loading (0–20 wt %), aiming to find how these parameters affect the products yield and properties of the treated oil. The results demonstrated that treating the crude duckweed bio-oil in subcritical water with or without catalyst under either H₂ or CO environment effected several desirable changes in the oil. Compared to H₂, using CO as initial gas led to treated oil with higher yield, lower viscosity, and higher hydrogen, and could also achieve larger energy recovery. Higher temperatures and longer reaction times produced treated oil with better quality but at the expense of reducing oil yield, respectively, due to the increased coke and gas formation. Larger catalyst loading was also favorable in realizing high quality treated oil, but it also promoted the production of coke and water-soluble material. During the treatment, the oxygenates in the crude duckweed bio-oil were more reactive than that of the nitrogenates, especially with catalyst. The higher heating values of the treated oils were estimated within the range 34.3–38.2 MJ/kg. CO₂ was the dominant gas formed under either CO or H₂ environment. Thus, this study suggested that the crude bio-oil from the HTL of duckweed can be effectively upgraded in subcritical water

Highly Active and Selective Photocatalytic Oxidation of Organosilanes to Silanols

Silanols are ubiquitous building blocks for organic synthesis and material fabrication. To date, a number of stoichiometric and catalytic methods have been developed for the direct oxidation of Si–H to Si–OH bonds. A common challenge in the oxidation of silanes is to combine both catalytic activity and selectivity. Herein, we report a highly active and selective photocatalytic approach for the oxidation of organosilanes to silanols. Using plasmonic Au-TiO2 as a photocatalyst for dimethylphenylsilane oxidation enables complete conversion (>99% yield) and high selectivity (98.3%) with catalytic activity up to 121.8 g g–1. The observed activity substantially exceeds those of most reported homogeneous and heterogeneous catalysts. Silanol synthesis could be achieved under mild conditions in either aqueous or solvent-free conditions and allows the oxidation of a broad scope of sterically hindered hydrosilanes in excellent yield and selectivity. The general concept of photocatalytic synthesis of valuable silanols is further demonstrated by five photocatalysts

Conversion of CO₂ into Organic Carbonates over a Fiber-Supported Ionic Liquid Catalyst in Impellers of the Agitation System

Herein, a fiber-supported imidazolium-based ionic liquid catalyst in impellers of the agitation system was developed for efficient cycloaddition of CO2 with epoxides under metal- and solvent-free conditions. The fiber-supported ionic liquid catalyst was designed collectively and synthesized systematically, and it was characterized in detail on the physicochemical properties via various technologies during both the preparation and utilization processes. Moreover, the influence of ionic liquid structures and reaction conditions on the cycloaddition was inspected, and the fiber catalyst-mediated CO2 conversion proceeded smoothly (100 °C and 1 MPa) in a gram-scale for the synthesis of organic carbonates in good to quantitative yields. Notably, the novel fiber catalyst in impellers of the agitation system also displayed prominent recyclability (21 cycles), and the protocol could be operated concisely with a good prospect for industrial applications

Fiber-Supported Poly(quaternaryammonium Bromide)s as Supported-Phase Transfer Catalysts in the Spinning Basket Reactor

In this paper, a newly developed fiber-supported poly­(quaternaryammonium bromide)­s, which served as an efficient and recyclable supported phase-transfer catalyst in the spinning basket reactor for a series of nucleophilic substitutions, is reported. The fiber catalysts were designed and synthesized systematically from commercially available polyacrylonitrile fiber, and the properties of fiber samples at different stages were characterized in detail by sorts of technologies. Moreover, the nucleophilic substitutions mediated with fiber-supported phase-transfer catalyst exhibited high efficiency to afford a range of substituted products in excellent yields (91–98%) under mild conditions, and on this basis, a solid–liquid phase-transfer catalysis mechanism was proposed. Markedly, the spinning basket reactor with fiber catalyst in its impellers revealed prominent recyclability at least for 15 cycles, and the concise method of operation also exerted a good perspective application in chemical industry

Chemoenzymatic Hunsdiecker-Type Decarboxylative Bromination of Cinnamic Acids

In this contribution, we report chemoenzymatic bromodecarboxylation (Hunsdiecker-type) of α,ß-unsaturated carboxylic acids. The extraordinarily robust chloroperoxidase from Curvularia inaequalis (CiVCPO) generated hypobromite from H2O2 and bromide, which then spontaneously reacted with a broad range of unsaturated carboxylic acids and yielded the corresponding vinyl bromide products. Selectivity issues arising from the (here undesired) addition of water to the intermediate bromonium ion could be solved by reaction medium engineering. The vinyl bromides so obtained could be used as starting materials for a range of cross-coupling and pericyclic reactions

Vanadium-Containing Chloroperoxidase-Catalyzed Versatile Valorization of Phenols and Phenolic Acids

The downstream product transformation of lignin depolymerization is of great interest in the production of high-value aromatic chemicals. However, this transformation is often impeded by chemical oxidation under harsh reaction conditions. In this study, we demonstrate that hypohalites generated in situ by the vanadium-containing chloroperoxidase from Curvularia inaequalis (CiVCPO) can halogenate various electron-rich and electron-poor phenol and phenolic acid substrates. Specifically, CiVCPO enabled decarboxylative halogenation, deformylative halogenation, halogenation, and direct oxidation reactions. The versatile transformation routes for the valorization of phenolic compounds showed up to 99% conversion and 99% selectivity, with a turnover number of 60,700 and a turnover frequency of 60 s–1 for CiVCPO. This study potentially expands the biocatalytic toolbox for lignin valorization

Hierarchically Hollow MnO₂@CeO₂ Heterostructures for NO Oxidation: Remarkably Promoted Activity and SO₂ Tolerance

Thermochemical approaches of oxidizing NO to NO2 have been considered as the critical steps governing NOx purification technologies. However, developing efficient materials with boosted NO oxidation activity and strong SO2 resistance at low temperature still remains a significant challenge. This contribution discloses a versatile and scalable methodology for the design of hollow MnO2@CeO2 heterostructures for NO oxidation. Due to its hollow core–shell nanostructure with a high density of active oxygen vacancies and improved charge-transfer efficiency induced by the heterojunction interface, the resulting material exhibits remarkable low-temperature catalytic activity in NO oxidation (T50 at 196 °C and T92 at 275 °C), achieving over 69 °C of temperature reduction in comparison with the commercial Pt/Al2O3 catalyst (T50 at 275 °C). Remarkably, the SO2 tolerance of the hollow core–shell material is greatly enhanced due to the block accessibility of the mesoporous CeO2 shell (ECeO2,SO2 = −1.78 eV vs EMnO2,SO2 = −1.04 eV). This work exemplifies an alternative perspective in the design of high-performance hollow core–shell nanostructured catalysts for atmospheric pollutant purification and industrial thermal catalysis processes

Modulating the Electrocatalytic Performance of Palladium with the Electronic Metal–Support Interaction: A Case Study on Oxygen Evolution Reaction

The present work reports a general approach to improve the electrocatalytic property of noble metal through regulating its electron status by introducing the electronic metal–support interaction (EMSI). As a case study, the catalytic activity of metallic Pd toward oxygen evolution reaction (OER) in alkaline solution has been significantly promoted by stabilizing Pd^δ+ oxidic species at the interface of the Pd–metal oxide support with the help of EMSI effect, suggesting an intrinsic advantage of Pd^δ+ in driving OER. We further demonstrate that the chemical state of Pd^δ+ can be easily modulated in the range of 2+ to 3+ by changing the metal oxide support, interestingly, accompanied by a clear dependence of the OER activity on the oxidation state of Pd^δ+. The high Pd³⁺ species-containing Fe₂O₃/Pd catalyst has fed an impressively enhanced OER property, showing an overpotential of 383 mV at 10 mA cm^–2 compared to those of >600 mV on metallic Pd and 540 mV on Fe₂O₃/glassy carbon. The greatly enhanced OER performance is believed to primarily derive from the distinctive improvement in the adsorption of oxygenated intermediates (e.g., *OH and *OOH) on metal-oxide/Pd catalysts. Moreover, similar EMSI induced improvements in OER activity in alkaline solution are also achieved on both of the Fe₂O₃/Au and Fe₂O₃/Pt, which possess the oxidic species of Au³⁺, and Pt²⁺ and Pt⁴⁺, respectively