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The ruthenium catalysed cross-metathesis of terpenoids with methyl acrylate and methyl methacrylate was used to prepare new terpenoids and to improve, to a large extent, the synthesis of known terpenoids. In particular, the cross-metathesis of mono-unsaturated terpenoids was very efficient whereas the transformation of terpenoids incorporating two double bonds was more difficult due to side reactions. The cross-metathesis reactions were carried out under environmentally friendly conditions either in dimethyl carbonate or under solvent-free conditions. [ABSTRACT FROM AUTHOR]

“The best catalyst is no catalyst.” With growing public concern over global warming and the amount of greenhouse gases, it is important to reduce the amount of chemicals and eliminate waste, to obtain better results in a simple, selective, safe, and environmentally benign fashion compared to conventional tedious chemical synthesis. Herein, we disclose an environmentally benign, rapid, catalyst/promoter/coupling reagent-free cyclization procedure of free amino acids to furnish exclusively cyclic dipeptides (2,5-diketopiperazines, DKPs) in excellent or even quantitative yield, along with their solid state self-assembling properties. This process is extremely simple and highly efficient with little or no traditional synthetic skills and without any chromatographic purification. Synthesis of structurally diverse DKPs has been achieved with a dramatic decrease in the reaction time, the amount/number of solvents used, a significant increase in the yield and nearly complete elimination of waste. As a result, this is an excellent example for the environmentally benign, clean and green chemistry concept. The most exciting outcome of our investigation is an unusual case of chiral self-recognition encountered upon the cyclization of rac-pipecolic acid, which resulted in the formation of the meso-product exclusively. [ABSTRACT FROM AUTHOR]

Chemical catalytic conversion of biomass-derived sugars to lactic acid has attracted considerable attention due to the cheap, abundant and renewable nature of biomass and its huge potential application in the synthesis of biocompatible and biodegradable polylactic acid resins. However, this route is still a huge challenge in view of the transformation efficiency. This paper reports a series of Zn-based catalysts, which are facile and cheap to prepare and highly efficient for the conversion of biomass-derived carbohydrates to ethyl lactate (EL). The microstructure, active site composition and surface properties were characterized by TEM, HRTEM, XRD, NH3-TPD, CO2-TPD, Py-IR, and XPS. The catalytic performance of catalysts in the conversion of biomass-derived carbohydrates to ethyl lactate (EL) and the effect of water content were investigated. It was found that the Zn species played a decisive role in regulating the strengths of the acidic and basic sites to match the rate of each reaction in the tandem reactions. The basic sites are beneficial for isomerization and retro-aldol condensation, while the temperature-responsive released H+ protons are responsible for the dehydration of triose to methylglyoxal, a rate-determining step in the conversion of triose to EL. Addition of a small amount of water could enhance the release of the protons and thus accelerate the dehydration reaction, but excessive water would favor the formation of humins. Using ZnSi-2 as a catalyst under optimal conditions, yields as high as 74.5% of EL from glucose, 81.0% from fructose, 70.9% from mannose, and 80.3% from sucrose could be achieved with tens of times higher productivity than the previously reported values in the literature. DFT calculations revealed that Zn(OEt)Cl, Zn(OH)Cl, and Zn(OH)(OEt) were probably the active components. In addition, the stability of the catalyst as well as the deactivation and regeneration was also studied. The findings in this research provide new insights into the exploration of efficient catalysts for biomass conversion to value-added chemicals. [ABSTRACT FROM AUTHOR]

The production of ammonia under ambient conditions has been a long-standing challenge for the chemical industry. The electroreduction of nitrate presents a promising solution for nitrate wastewater treatment and decentralized ammonia production. However, traditional Ag-based catalysts suffer from nitrate-to-nitrite conversion, leading to toxicity concerns and hampering ammonia preparation. In this study, we synthesized an innovative Ag–Cu–P catalyst that effectively tunes the d-band centre and electronic structure. The catalyst exhibited a remarkable NH4+ yield rate of 566.30 μmol cm−2 h−1 at −0.3 V (vs. RHE), reducing nitrite content to below the drinking water standard. Characterization results revealed a distinctive fern leaf-like morphology, providing an expanded active surface area. The challenge of facile nitrate conversion to nitrite on Ag-based catalysts has been addressed through the implementation of electronic structure modulation in this work. Theoretical calculations confirmed the substantial reduction in the energy barrier by modulating the d-band centre and electronic structure, facilitating the conversion of nitrite to ammonia. The regulation and analysis of d-band centres yielded valuable insights for catalyst material design. Meanwhile, direct evidence for potential intermediates has also been presented through in situ spectroscopy. These findings hold significant potential for practical applications, such as enhanced wastewater treatment and decentralized ammonia production, and provide support in the pressing need for sustainable ammonia synthesis under ambient conditions. [ABSTRACT FROM AUTHOR]

Hexamethylenediamine (HMDA), a crucial precursor of nylon-66, can be synthesized from caprolactam (CPL) via a two-step route involving CPL ammoniation and 6-aminocapronitrile (ACN) hydrogenation. Based on theoretical calculations and experimental screening, mesoporous alumina was selected which served as a highly active and cost-efficient catalyst for CPL ammoniation, catalysing the ring-opening of amides by C–N bond breakage and subsequent amide dehydration to nitrile. A 57.9% CPL conversion and 98.3% ACN selectivity were achieved at 320 °C with stability over 480 hours. The subsequent hydrogenation of ACN using the commercial RANEY® Ni catalyst yielded 100% HMDA, requiring milder conditions and half the hydrogen compared to adiponitrile processes. Overall, this research highlights a green HMDA production pathway, employing CPL as a feedstock. [ABSTRACT FROM AUTHOR]

2,5-Furandicarboxylic acid (FDCA) is one of the most promising biodegradable substitutes for fossil-derived terephthalic acid (PTA) and adipic acid. The production of FDCA from biomass-derived 5-hydroxymethylfurfural (HMF) is significant and has attracted great attention. However, the major challenge lies in the development of a non-precious metal-based catalyst system without employing a homogeneous base. Herein, we successfully prepared an atomically dispersed Fe–N–C/γ-Al2O3 catalyst, which affords superior catalytic performance in terms of activity and stability with a FDCA yield of 99.8% and reusability of five recycle times in the catalytic oxidation of HMF to FDCA under base-free mild conditions. Based on controlled experiments and complementary characterization studies, we found that the atomically dispersed medium-spin Fe–N5 active sites together with the surface acidic/basic sites of alumina synergistically enhanced the catalytic activity and selectivity towards FDCA under base-free conditions. Our process eliminates the employment of expensive oxidants and corrosive bases, leading to economic and green biomass transformations. [ABSTRACT FROM AUTHOR]

Single atom-based catalysts (SACs), due to their exceptional electrocatalytic behavior, have been explored for numerous applications such as the oxygen reduction reaction, thermo-catalytic CO2 reduction, and other catalytic activities. Ammonia is one of the most used chemical compounds, and its electrochemical synthesis is a promising alternative as it is simple and cost-effective and shows selective tunability towards the synthesis. Utilizing single-atom electrocatalysts with comparatively low metal mass loading yet exceptional activity could be a better approach to maximize ammonia production. Herein, we report a practically viable magnesium SAC (MgNxC) for the promising reduction of nitrate to ammonia. The catalyst was prepared using green leaf extracts of Spinacia oleracea via simple one-step pyrolysis. We optimized their synthesis temperature to scrutinize the effect of SAC formation and their variation on the catalysis efficacy. The MgNxC650 catalyst, anchored on a defective graphitic matrix, exhibits the best-optimized potential of −0.58 V vs. RHE, a faradaic efficiency of 81.5 ± 2.9% and a yield rate of 392.5 ± 41.2 μmol h−1 mg−1cat. with excellent repeatability. A comprehensive study of the nature of the heterojunction formed at the reactive interface of MgNxC catalysts was carried out by Mott–Schottky analysis to probe the band structure of the intrinsically induced metal–semiconductor junction in the MgNxC catalysts, followed by the analysis of parameters like flat band potential and carrier density correlation. DFT is employed to optimize the most stable reactive site and various reaction pathways for favorable nitrate reduction reaction with probable reaction intermediates were explored. Collectively, our work demonstrates a simple, cost-effective, and convenient way to synthesize SACs. Moreover, it provides clear evidence that chlorophyll moieties can be used as a template to prepare metal catalysts singly anchored on the graphitic carbon matrix. [ABSTRACT FROM AUTHOR]

Biomass provides a promising source of carbon for obtaining environment-friendly carbon materials, but obtaining heteroatom-doped carbon materials (HDCMs) from biomass directly by a green method still remains challenging. This study successfully synthesized nitrogen and phosphorus co-doped porous carbon materials (Y-NPC) by the simple in situ pyrolysis of renewable yeast mixed with water from 800 to 950 °C. Various characterization methods show that nitrogen and phosphorus are doped into the carbon skeleton and mainly exist in the forms of graphite-N, pyridine-N, C–P, P–N, and P–O states. The catalyst Y-NPC-900 °C with a 3D hierarchical porous structure and high P–N content exhibited superior nitro hydrogenation performance and reaction stability using molecular hydrogen and hydrazine hydrate as hydrogen sources under mild conditions. Density functional theory (DFT) calculations and experiments attributed the exceptional catalytic performance to hydrogen activation and the good adsorption ability of substrates over N, P co-doped carbon (NPC). Therefore, this research proposes an eco-friendly and simple synthesis strategy for in situ N, P co-doping metal-free carbon catalysts derived from biomass, showing the significance of N, P co-doping and single N- or P-monodoping in the charge distribution of carbon materials. [ABSTRACT FROM AUTHOR]

We have developed a straightforward electrochemical protocol for direct α-amidation and α-pyrazolation of N-alkoxy- and N-aryloxycarbonyl pyrrolidines with amides or pyrazoles. Unlike previously reported methods, this protocol does not require pre-prepared amidation reagents, thereby shortening the synthesis route and boosting atom economy. Various functional groups are tolerated, and the reaction proceeds at room temperature in only 2.5 h without assistance from chemical oxidants or catalysts. [ABSTRACT FROM AUTHOR]

The field of converting methane into valuable products using renewable energy sources under ambient conditions is both appealing and highly demanding. The inherent inertness of methane (CH4) necessitates the selective breaking of its first C–H bond while avoiding excessive oxidation, in order to transform CH4 into high-value products. Herein we present a novel approach for creating a highly concentrated Ni0/Ni2+-on-Cu interface using an O2 cold plasma in situ method to enhance the activity and stability of the CH4OR to low-carbon alcohol. The Cu@Ni–NiO electrocatalyst exhibits excellent performance for the CH4OR to low-carbon alcohol, showcasing a high faradaic efficiency (FE) of 86.7%, an impressive low-carbon alcohol yield of 1215.2 μmol g−1 h−1, remarkable durability (66 h) and a notable C2H5OH selectivity of 59.8% at 1.9 V vs. RHE. The ATRSEIRAS spectroscopy and DFT calculations further reveal that the synergistic effect of the Ni0/Ni2+-on-Cu interface can enhance the *O and *CH2 generation on Ni0, and the *CH2 spillover from Ni0 to Ni2+ atoms can also improve the C–C coupling reaction. Additionally, the in situ treatment with O2 cold plasma can enhance the formation of NiO, leading to a high concentration of the Ni0/Ni2+-on-Cu interface, which effectively prevents the oxidation of Ni0 during the CH4OR process. Furthermore, we developed a general oxidation strategy for the direct synthesis of transition metal nitrides by O2 cold plasma treatment of Ni0. Compared with the previous methods used for the preparation of NiO, the Ni-based metal oxide synthesis method offers several advantages, including simplicity and practicality, low cost, high throughput, pollution-free nature, low energy consumption and the capability to prepare metal oxides with controllable coordination number of the O atom. This work provides new insights into the highly efficient CH4OR process and presents an innovative, cost-effective method for preparing electrocatalysts. [ABSTRACT FROM AUTHOR]

The design and development of self-supporting multifunctional catalysts for efficient water splitting and long-life rechargeable zinc-air batteries (ZABs) is of great significance for energy conversion. Different from previously reported metal layered double hydroxides (LDHs) grown on metal phosphides, herein, we synthesize a CoNi-LDH precursor with a larger exposed surface area on a stainless-steel mesh (SSM), followed by direct surface phosphating to form NiCoP@CoNi-LDH. The obtained NiCoP@CoNi-LDH/SSM demonstrated enhanced HER, OER and ORR properties compared to the CoNi-LDH/SSM precursor, and comparable to or even superior to those of commercial catalysts. Moreover, when applied as the aircathode of a ZAB, it can continue to operate for a long lifetime of more than 1500 h during charge and recharge testing at a current density of 10 mA cm−2, with a low voltage gap of only 0.81 V before 900 h. Additionally, the assembled ZAB can efficiently drive a two-electrode water-splitting experiment. The acquired voltage is only 1.579 V when the output current density is 10 mA cm−2, which is much lower than that of the CoNi-LDH/SSM precursor (1.719 V), or even the commercial Pt/C/SSM∥RuO2/SSM (1.626 V) electrode pair. After deeply analyzing the insight into the influence of the surface phosphating, we confirmed that both the generated NiCoP@CoNi-LDH heterojunction and the formed NiCoP nanoneedle enhanced the inherent multifunctional properties of NiCoP@CoNi-LDH/SSM. This work provides a superior trifunctional catalyst, and we believe that it will advance a novel idea for the design of efficient multifunctional nanomaterials. [ABSTRACT FROM AUTHOR]

Furfural is a large-volume and widely available biomass-derived platform compound, and its transformation into valuable pentanediols is important for the sustainable production of bio-based polymers. Herein, we report a new catalyst system composed of Pt–Fe bimetallic nanoparticles highly dispersed on a commercial magnesium titanate (MT) support. HAADF-STEM, CO-DRIFTS and XPS characterization studies revealed that Pt was in the metallic state with a particle size of 1–2 nm, while Fe existed as Fe2+ and was decorated on the Pt particles. The electron transfer from Fe to Pt weakened the hydrogenation activity of the furan ring and meanwhile promoted selective ring-opening to 1,2-pentanediol (1,2-PeD). Reaction kinetics studies revealed the reaction rate with respect to hydrogen pressure was close to zero order, which allowed the reaction to proceed at a hydrogen pressure as low as 0.1 MPa. Under mild conditions of 140 °C and 0.1 MPa, the 0.1Pt0.05Fe/MT catalyst offered by far the highest production rate of 178 mol 1,2-PeD per mol Pt per hour, and the Pt–Fe bimetallic catalyst was stable during 200 h of time-on-stream, showing great potential for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, 2-methylquinoline compounds were synthesized continuously from nitroarenes and the ethanol/water system by a simple hydrogen transfer reaction in the presence of the Ru–Fe/γ-Al2O3 catalyst. This new simple synthesis reaction was heterogeneous and continuous. At the same time, green solvents were used, and strong acids, oxidants, and other environmentally harmful substances were not added, which conformed to the principles of green chemistry. Through the impregnation method, the nanocatalysts with a smaller particle size and uniform dispersion were obtained on the γ-Al2O3 particles (1–2 mm) and had good activity. The effects of the alcohol water volume ratio, pressure, flow rate and Ru–Fe mass ratios on the yields of 2-methylquinoline compounds in the reaction were investigated. The reaction can proceed smoothly for nitroarenes with different substituents, and a moderate to good yield (46%–88%) was obtained. [ABSTRACT FROM AUTHOR]

The highly efficient synthesis of benzoxazole, benzothiazole and benzimidazole has attracted much attention due to their superior biological activities. However, developing environmentally friendly and poisoning-resistant catalysts in heterogeneous catalytic systems remains a critical challenge. Herein, an atomically dispersed Co1/NC catalyst was fabricated by facile pyrolysis of a zeolitic imidazolate framework (ZnCo-ZIF). The Co1/NC catalyst exhibited excellent oxidation catalysis, sulfur-resistance and reusability performance. The mass specific activity (MSA) of Co1/NC was up to 42.0 mol2-PBO molCo−1 h−1, much higher than that of the Co/NC nano-catalyst (15.6 mol2-PBO molCo−1 h−1). Mechanism studies showed that O2 was activated by atomically dispersed Co active species to form 1O2 and ˙O2−, which were responsible for the dehydrogenation of the key imine intermediates to produce 2-phenylbenzoxazole (2-PBO). The current work represents a novel feasible strategy for the synthesis of bioactive heterocyclic compounds using efficient, stable and green heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

Furfural is an industrial renewable platform chemical, which can be converted to useful furanics such as α-angelica lactone, carboxylic acids such as levulinic acid and valeric acid, or to higher carbon content products via condensation routes for producing drop-in fuel replacements and chemicals with diverse applications. These important conversion processes may be carried out in selective fashions, although they require adequate catalysts. They were successfully carried out using versatile, stable silica-wrapped niobium oxide nanostructured catalysts. For example, α-angelica lactone was converted in an integrated fashion to ethyl levulinate in 90% yield, and the esterification of levulinic and valeric acids gave ethyl levulinate in quantitative yield and ethyl valerate in 90% yield, respectively, at 140 °C. Catalytic, mechanistic and kinetic modelling studies shed light on the influence of the materials properties on the catalytic performances. These catalysts outperformed pure Nb2O5, as well as hydrothermally synthesized composites consisting of Nb2O5 nanoparticles embedded in a mesoporous siliceous matrix. [ABSTRACT FROM AUTHOR]

Lignin is composed of phenylpropyl alcohol through the C–O and C–C bonds, where β-O-4 accounts for the majority. Self-transfer hydrogenolysis (STH) is a promising method to produce valuable chemicals and fuels from lignin by cleaving the β-O-4 bond without exogenous hydrogen, but all the reported work used noble metal-based catalysts. In this work, a highly efficient Ni/C catalyst was derived from a Ni-containing metal–organic framework (Ni-MOF), and its self-transfer hydrogenolysis performance towards ether bonds in lignin model compounds was evaluated using 2-phenoxy-1-phenylethanol as a model compound in detail. It was found that the catalyst pyrolyzed under a nitrogen atmosphere at 500 °C (Ni-NDC-500) was very efficient for the reaction. Moreover, it could also catalyze the reaction of native lignin into monomers effectively without exogenous hydrogen. In addition, Ni-NDC-500 was recycled three times without an obvious reduction of the activity. [ABSTRACT FROM AUTHOR]

The nucleophilic ring opening of epoxides by carboxylic acids is an indispensable transformation for materials science and coating technologies. Due to this industrial significance, improvements in operational energy consumption and catalyst sustainability are highly desirable for this transformation. Herein, an efficient, environmentally benign and non-toxic halide free cooperative catalyst system based on an iron(III) benzoate complex and guanidinium carbonate is reported. The novel catalyst system shows improved activity over onium halide catalysts under neat conditions and in several solvents, including anisole and nBuOAc. Detailed mechanistic studies using FeCl3/DMAP as a catalyst revealed the importance of a carboxylate bridged cationic trinuclear μ3-oxo iron cluster and guanidinium carbonate or DMAP as a carboxylate reservoir due to its superior activity. [ABSTRACT FROM AUTHOR]

The biorenewable carbohydrate-derived rigid building block of isosorbide (ISB) has demonstrated potential in high-performance polymer materials; however, a controllable eco-friendly preparation technology is not yet available. For this purpose, a sustainable strategy to synthesize ISB-based polycarbonate (PIC) has been established by adopting the CO2-based compound dimethyl carbonate (DMC) as a monomer and ionic liquids (ILs) as metal-free catalysts. The molecular weight of PICs can be readily controlled by varying the cation structure of IL catalysts. Control experiments, density functional theory (DFT) calculations, and Kamlet–Taft solvent parameters indicated that the H-bond donor/acceptor (HBD/HBA) ability of IL catalysts played a dominant role in regulating catalytic activity. PIC molecular weight can be modulated by modifying the inherent difference in reactivity of endo-OH and exo-OH in ISB, wherein the chain length or substituent group of cations can regulate the HBD/HBA ability of IL catalysts and anions can specifically activate the carbonyl carbon of DMC. The experimental results revealed that a task-specific [Pmim][OAc] catalyst exhibited the highest catalytic activity, which is attributed to its significant role in considerably lowering the disparity in reactivity between endo-OH and exo-OH. For this DMC route, the [Pmim][OAc] catalyst offered a PIC with the highest molecular weight of 57 200 g mol−1 reported to date. Furthermore, a well-supported polymerization mechanism was proposed, in which [Rmim][OAc]'s anion–cation synergistically catalyzed ISB and DMC to prepare PIC. Our findings offer a clear pathway for designing efficient metal-free catalysts to enable the sustainable synthesis of high molecular weight PICs, thus expediting the industrialization of the DMC route. [ABSTRACT FROM AUTHOR]

The wide application of lithium-ion batteries (LIBs) for electric vehicles forebodes a future decommissioning tide of spent LIBs. Therefore, the recycling of spent LIBs has garnered significant attention, primarily due to the scarcity of resources and the detrimental effects of environmental pollution. However, traditional recycling technologies such as pyrometallurgy and hydrometallurgy methods are limited by their high energy consumption, high pollution, and complicated separation processes. Herein, we propose a novel and general approach to convert a series of spent LiNi1−x−yCoxMnyO2 (NCM) cathodes into Ni–Co–Mn hydroxide (NCM-OH) catalysts for the oxygen evolution reaction (OER) using deep eutectic solvents to extract valuable metals, followed by an in situ precipitation process using oxalic acid and a final self-templating process in an alkaline solution. The NCM-OH catalyst obtained from the spent LiNi0.33Co0.33Mn0.33O2 cathode is found to possess a nanoflake-assembled microrod structure with a large surface area (385.8 m2 g−1) and high porosity, which is endowed with abundant active sites and gas channels for the electrocatalytic reaction and mass transfer process. As a result, the NCM-OH catalyst for the oxygen evolution reaction exhibits a low overpotential of 273 mV at a current density of 10 mA cm−2 with a Tafel slope of 50.46 mV dec−1 as well as satisfactory stability. The effect of the composition on the catalytic performance is also evaluated by comparing different Ni1−x−yCoxMny hydroxide catalysts derived from commercially prevailing spent cathodes. This work provides a promising strategy for recycling spent LIBs into electrocatalyst materials for the OER. [ABSTRACT FROM AUTHOR]

To replace the noble metals used in hydrodeoxygenation (HDO) catalysts, guaiacol HDO was conducted using various transition metal-loaded catalysts. Co/TiO2 was highly active for guaiacol HDO, enabling a more economic removal of the methoxy groups compared to the Ru/TiO2 catalyst, resulting in superior cyclohexanol selectivity. When a WO3 promoter was added to the Co catalyst to enhance its oxygen removal ability, the conversion of guaiacol was severely reduced because the co-impregnated WOx species decreased the number of exposed Co sites. To avoid this phenomenon, Co and WO3 were isolated by physically mixing Co/TiO2 and WO3/TiO2, where 100% conversion and oxygen removal could be achieved under 10 bar H2 at 250 °C. The cause of the catalyst deactivation was systematically investigated by magnetic separation of the physical mixture of the catalysts after the reaction, followed by a series of characterization studies. Temperature-programmed-oxidation mass spectroscopy and Raman spectroscopy revealed that the deposition of carbonaceous species was the main contributor to the deactivation of WO3/TiO2, and the catalytic activity could be successfully recovered by simple calcination at 400 °C. This study provides insights into the development of economical and efficient physically mixed HDO catalysts using transition metals, and contributes to the understanding of the deactivation and regeneration of physically mixed HDO catalysts. [ABSTRACT FROM AUTHOR]

In 2011, Zhang's research team, in cooperation with Li and Liu, reported the Pt1/FeOx atomically dispersed catalysts for the first time in the world, and based on this, proposed the concept of "single-atom catalysts". Single-atom catalysts (SACs) have a wide range of industrial application prospects in the catalytic synthesis of fine chemicals due to their high atomic utilization rate and special catalytic activity. With the deepening of the research, the preparation methods of SACs emerge in an endless stream, but it is still an urgent problem to realize the industrial production of highly stable SACs prepared in small batches (gram level) or even in large batches (kilogram level). In this review paper, several typical solvent-free green synthetic strategies (e.g., ball milling, physical mixing, gas migration, and pyrolyzing coordination polymers (including MOFs)) for the batch preparation of SACs are introduced. And typical catalytic application of SACs in green synthesis of fine chemicals by means of oxidation reaction, hydrogenation reaction, coupling reaction and other reactions are also introduced. This is the first review paper focusing on the mass preparation techniques of SACs and their applications in fine chemicals production. [ABSTRACT FROM AUTHOR]

The isomerization–dehydration cascade conversion on the saccharide platform is a pivotal route for biomass valorization, although it exhibits a specific reaction complexity that makes achieving an efficient conversion a highly technical challenge. The rational design of novel versatile solid acids is deemed to be the key to improving the cascade catalytic performance. In this paper, a dual-functional carbon-based solid acid catalyst (DFCSA) with tunable Brønsted/Lewis acid sites was developed for the cascade conversion of saccharides. The combined modification of H3PO4 and HNO3 on the carbon substrate contributed to the grafting of protonated moieties with a reasonably porous structure. With the aid of AlPO4, which has an orthorhombic crystal structure, the newly developed catalyst was able to achieve good performance for the subsequent hydrothermal conversion. Under optimal conditions, glucose and xylose were transformed with high product yields: 38.2 mol% levulinic acid and 69.7 mol% furfural, respectively. In addition, the catalyst displayed excellent hydrothermal stability, with only a slight degradation in activity after 10 cycles, which was ascribed mainly to the high thermal stability of AlPO4 and the firm grafting of the surface functional groups. As shown by the kinetic analysis, the DFSCA catalyst had a higher conversion rate and lower activation energy in the cascade conversion of xylose than that of glucose, leading to a better yield of furfural. [ABSTRACT FROM AUTHOR]

Deliberate engineering of built-in electric fields (BEFs) can facilitate electron transfer and promote asymmetrical charge distribution, thereby regulating the adsorption/desorption of reaction intermediates. Herein, an oxygen-deficiency-rich MnO-CeO2 is synthetized supported on a carbon sphere (MnO-CeO2@Cs), adeptly crafted with a prominent work function difference (ΔΦ) and robust BEF, targeting the electrocatalytic oxygen reduction reaction (ORR). Empirical and theoretical results substantiate that the BEF triggers interfacial charge redistribution, fine-tuning the adsorption energy of oxygen intermediates and hastening reaction kinetics. Consequently, the MnO-CeO2@Cs showcases commendable performance (E1/2 = 0.80 V and jL = 5.5 mA cm−2), outshining its single-component counterparts. Impressively, the MnO-CeO2@Cs-based zinc–air batteries (ZABs) boast an exemplary power density of 202.7 mW cm−2 and enduring stability of 297 h. Additionally, the solid-state ZAB commands a peak power density of 67.4 mW cm−2, underscoring its potential in flexible ZAB applications. This work delineates a strategic avenue to harness interfacial charge redistribution, aiming to enhance the catalytic performance and longevity of energy conversion/storage apparatuses. [ABSTRACT FROM AUTHOR]

The enhancement of 3D character in chemical scaffolds has become an unavoidable space and a key component for diverse applications. Herein, we report a simple phenol-derived catalyst with synergistic involvement of electronic and electrostatic sites to access spirocyclic carbonates from spiroepoxy oxindoles and carbon dioxide. The metal-free and co-catalyst free catalytic system demonstrates excellent activity in synthesizing diverse spirocyclic carbonates with good conversions (up to 99%) under ambient reaction conditions. Volumetric and NMR investigations enabled the synergistic role of the key chemical functionalities in the catalyst and elucidated the probable reaction mechanism. The calculated values of different green metrics revealed the suitability and practical applicability of the catalytic system. [ABSTRACT FROM AUTHOR]

The Friedel–Crafts arylation is among the most known organic reactions, usually being promoted by a Lewis acid, that have been employed for the synthesis of bis-indolyl methanes. Herein, we report a mild, inexpensive, green and organocatalytic protocol for the promotion of a Friedel–Crafts-type reaction between indoles and aldehydes, where N-heterocyclic iod(az)olium salts are utilized as halogen-bonding catalysts, leading to the double addition of the indole motif. A variety of aliphatic and aromatic aldehydes were converted into diarylmethanes in good to high yields, while the scope of indoles was also investigated. Water was employed as the solvent, while the reaction time was short. The reaction mechanism was also studied. [ABSTRACT FROM AUTHOR]

Herein we evaluate the promotive effect of Au and Sn incorporation into supported Pd nanoparticles for the direct synthesis of H2O2 from molecular H2 and O2. The introduction of both secondary metal modifiers was found to result in a significant enhancement in catalytic performance, although, in the case of the PdSn system, it was identified that relatively large quantities of the secondary metal were required to rival the activity observed over optimal Au-containing formulations, with the 0.25%Pd–2.25%Sn/TiO2 catalyst offering comparable H2O2 synthesis rates to the optimised 0.25%Pd–0.25%Au/TiO2 formulation. The introduction of Sn was found to considerably improve Pd dispersion, correlating with an improvement in selective H2 utilisation. Notably, the optimal PdSn catalyst identified in this work achieves superior H2O2 selectivities compared to the PdAu analogue and is able to rival the performance of state-of-the-art materials. [ABSTRACT FROM AUTHOR]

The selective depolymerization of PET plastics to p-xylene (xylene) is very challenging owing to the full deoxygenation of the terephthalic acid monomer and the retainment of the benzene ring through saturation. In this study, the modification of Co–Al catalysts by introducing a second metal (Fe, Cu, Ni, or Zn) was conducted to tailor the activity of the cobalt species for the conversion of PET to xylene. The results indicated that the CoFe alloy in the Co–Fe–Al catalyst weakened the adsorption/activation of H2, achieving xylene yields of >99.0% from PET. Co–Fe–Al suppressed the ring hydrogenation of the benzene ring, while Co–Al and Co–Ni–Al catalyzed the hydrogenation of the benzene ring and cleavage of the C–C bond in the intermediates. Benzene ring-containing intermediates showed a high affinity for Co–Ni–Al and Co–Al, facilitating their hydrogenation. Co–Fe–Al could preferably adsorb and activate the oxygen-containing functionalities of the intermediates for the deoxygenation reactions. The hydrogenolysis reaction of C–OH in intermediates, like 1,4-benzenedimethanol (Ea: 137.8 kJ mol−1), was the rate-determining step, while the hydrogenation of the carboxylic intermediates was much easier. [ABSTRACT FROM AUTHOR]

Despite the remarkable advances in the research field of asymmetric catalytic oxidation reactions via hypervalent iodines with simple procedures, high level of efficiency and stereoselectivity and the development of their highly scalable, environmentally benign, and sustainable protocols under the greener organocatalysis paradigm for further industrial translations remains a long-standing challenge in synthetic organic chemistry and process engineering over the past few decades. Herein, we design and synthesize a new library of conformationally flexible and recyclable aryl iodine catalysts by utilization of (i) industrial waste (chloramphenicol base) as the scaffold and (ii) inexpensive amino acid residue (threonine) as the chiral source. Our chiral aryl iodine(III) catalysts bearing H-bond donors and a tunable chiral pocket have been successfully applied in diverse, robust asymmetric oxidative transformations, e.g., dearomatization, spirolactonization, direct C(sp2)–H/C(sp3)–H cross coupling, and fluoridation. Our processes feature a column isolation-free approach, easy-handling operation, and upscaling synthesis with the catalysts being facilely recycled, in particular via precipitation. [ABSTRACT FROM AUTHOR]

In this work, the reaction pathways of one-step glycerol hydrodeoxygenation in the gas phase are exploited under flow conditions over molybdena-based catalysts (8.7 wt% Mo/black carbon). Hydrodeoxygenation (HDO) experiments with possible reaction intermediates along with temperature-programmed surface reaction spectroscopy (TPSR) experiments demonstrated two possible reaction pathways. The major one involves propylene formation via hydrodeoxygenation of 2-propen-1-ol which is considered to be the main intermediate of the reaction. In the secondary route, propanal formed via 2-propen-1-ol isomerization is further converted to 1-propanol. XPS measurements in fresh-reduced and reduced-used catalysts revealed that molybdena exists as multivalent species mostly as Mo5+, Mo4+ and Mo3+, the presence of which seems to be crucial for the desired pathway of successive HDOs towards propylene. TPSR tests using methanol as the probe molecule showed that redox and acid sites co-exist on the surface of reduced molybdena catalysts, and this bifunctionality is mostly served by the undercoordinated molybdena species. The long-term catalyst test at 280 °C and 60 bar pressure under glycerol hydrodeoxygenation conditions demonstrated that the catalyst remains stable in terms of activity and selectivity for the first 10 h with a gradual drop afterwards. Regeneration of the catalyst for a short time under hydrogen flow proved to be sufficient to fully recover the initial activity and product selectivity. [ABSTRACT FROM AUTHOR]

para-Xylene (PX) is a basic building block of polyethylene terephthalate, which is currently produced from petroleum resources. Developing a renewable route to PX is highly desirable to address both economic and environmental concerns. Several attempts used noble metal catalysts, e.g. Pd/Al2O3, to synthesize PX from biomass-derived 4-methyl-3-cyclohexene-1-carboxaldehyde (4-MCHCA), but suffered from a severe decarbonylation reaction, resulting in toluene as the main product. In this paper, we report an FeOx modification strategy to suppress the decarbonylation reaction on a Pd/Al2O3 catalyst, leading to a drastic shift in selectivity towards PX with a yield up to 81% via a cascade dehydroaromatization–hydrodeoxygenation (DHA–HDO) pathway. Characterization and control experiments revealed that the electron density of Pd sites decreased in an FeOx-modified Pd/Al2O3 catalyst compared to Pd/Al2O3, thus tuning the preferential adsorption mode of the substrate from η2-(C,O), the key transition state of the decarbonylation reaction, to the η1-(O) mode that favors the hydrodeoxygenation process. Notably, this designed catalyst is highly stable and is readily applicable in the selective synthesis of a broad range of desired aromatic chemicals via the same DHA–HDO pathway from cyclohex-3-enecarbaldehyde derivatives. Overall, this work develops a controllable catalyst modification strategy that tailors an efficient catalyst for petroleum-independent bio-PX synthesis. [ABSTRACT FROM AUTHOR]

Iron-catalysed 1,2-acyl migration of tertiary α-azido ketones and 2-azido-1,3-dicarbonyl compounds provides a simple and atom-economical approach toward enamides and isoquinolones. This paper reports two catalyst systems for these transformations which employ iron(II) complexes [Fe(dpbz)]Br2 (dpbz = 1,2-bis(diphenylphosphino)benzene) and FeBr2/Et3N, respectively. [Fe(dpbz)]Br2 was found to be highly effective at converting 2-azido-2,3-dihydro-1H-inden-1-ones to isoquinolones. The reagent combination of FeBr2/Et3N, on the other hand, exhibited a broader catalytic scope, owing to the beneficial effect of Et3N. This latter catalyst system enables 2-azido-2-methyl-1,3-dicarbonyl compounds to be converted to the corresponding enamides under mild conditions in good yields. [ABSTRACT FROM AUTHOR]

We disclose a metal-free, iodine-catalyzed oxidative C–H sulfenylation and selenation of alkenes, particularly 1,1-diarylethenes with diorganyl dichalcogenides in water for the cost-effective, highly atom-economical, and sustainable synthesis of valuable vinyl sulfides and selenides including some aggregation-induced-emission (AIE) active molecules. The transformation required only 10 mol% iodine as the catalyst and a very small amount of a green oxidant, H2O2 (0.3 equiv.), to afford the desired products in moderate to high yields of up to 96% under mild reaction conditions, i.e. 50 °C and an aerobic atmosphere. The products were further synthetically diversified to various novel classes of organic molecules. The notable advantages of this method over the previously developed ones for the C–H chalcogenation of 1,1-diarylalkenes are (a) a metal-free, energy-efficient, cost-effective and sustainable protocol for the synthesis of both vinyl sulfides and selenides, (b) use of inexpensive reagents such as iodine as the catalyst and H2O2 as the green oxidant, (c) water as the green reaction medium and water as the only byproduct, (d) a straightforward scale-up process up to the gram scale without any compromise on the reaction outcome, (e) very clean reactions (100% conversion) in multiple cases to afford pure vinyl sulfides/selenides without the requirement of a huge organic-solvent consuming column chromatographic purification technique, and (f) excellent green chemistry metrics such as high atom economy (>96%), atom efficiency (≥87%), carbon efficiency (>88%), and reaction mass efficiency (≥81%), a very low E-factor (≤4.5 g waste per g product), here the byproduct is nothing but water, and a very high EcoScale score (≥82) which revealed that this method is excellent in the context of green chemistry. Moreover, the catalyst iodine could be recovered after the reaction and recycled without any compromise on the reaction outcome which makes the process highly sustainable. Mechanistic studies revealed a radical pathway for this transformation. [ABSTRACT FROM AUTHOR]

Electrochemical valorization of bulk chemicals to produce value-added fine chemicals is highly attractive and deemed to be a green and economic way to optimize traditional industrial synthesis. The electrochemical methanol upgrading (EMU) process which converts methanol to value-added formate exhibits an expectation of high profit and adherence to the tenets of green chemistry, and it has received substantial interest aimed at discovering highly efficient catalysts with satisfactory operational stability. In this work, focusing on enriching and activating the high-valence cobalt active sites, a hierarchically nanoporous nitrogen-doped carbon-supported Co/CoO hybrid catalyst grown on cobalt foam (Co–N–C/CoO/CF) was fabricated. The high porosity and conductive microchannels could synergistically enrich the local high-valence Co active sites and boost the in situ generation of such sites via an electrochemical pre-oxidation process. Benefitting from the synergy of multiple structural benefits, the Co–N–C/CoO/CF catalyst exhibits robust EMU performance. An ultralow potential of 1.309 V versus a reversible hydrogen electrode can be identified to drive a 50 mA cm−2 EMU current density, and a high faradaic efficiency (FE) of 98.2% can be achieved. In addition, with the merits of high structural stability, excellent operational stability can be achieved for Co–N–C/CoO/CF with negligible degradation in either current density or FE for at least 120 h, making the catalyst the most stable catalyst to date for methanol-to-formate upgrading. Its high activity and excellent operational stability make the Co–N–C/CoO/CF catalyst a promising candidate for green and economic formate electrosynthesis via partial methanol electro-oxidation. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) can be recovered as high-purity bis(2-hydroxyethyl terephthalate) (BHET) monomer by glycolysis in the presence of Fe3O4 nanoparticles (NPs). In this study, Fe3O4 NPs of various shapes, sizes, and surface areas were synthesized using different colloidal synthesis methods, and the conversion of PET glycolysis and BHET yield were compared. Spinel ferrite NPs, including Fe3O4, were synthesized using the coprecipitation (CP), thermal decomposition (TD), and the hydrothermal (H) methods. Among the NP catalysts, Fe3O4-CP exhibited the best glycolysis performance with a PET conversion of ∼100% and BHET yield of 93.5% at 195 °C for 2 h owing to its high surface area (146.6 m2 g−1). The larger the surface area and the better the dispersion, the higher the glycolysis activity. The glycolysis performance of the mixed spinel ferrite NPs was similar to that of the Fe3O4 NPs, indicating that replacing Fe2+ in the Fe3O4 NPs with other transition metals, M2+, did not significantly change the glycolysis performance. BHET monomers produced from commercial waste PET bottles in large quantities contained trace amounts of metal contaminants, because PET production uses various metal-based additives and catalysts. Amberlite IRC-120, a cation-exchange resin, effectively removed metal impurities from BHET. This study provides an effective strategy for producing recycled PET (r-PET) by waste PET glycolysis. [ABSTRACT FROM AUTHOR]

The catalytic hydrosilylation of alkenes is a major industrial reaction and a very efficient and atom-economical way to obtain functional organosilane compounds and cross-linked materials. Platinum-based catalysts are currently preferred in the industry despite the low availability and high cost of platinum but considerable efforts are being directed to replace Pt with non-noble metals. In this context, we developed a robust and highly active non-noble metal catalytic system using commercially available MnBr(CO)5. It was successfully employed in olefin hydrosilylation reactions using various functional olefins and industrially relevant silanes such as 1,1,1,3,5,5,5-heptamethyltrisiloxane (MDHM) and polymethylhydrosiloxanes (PMHS). This system tolerates unpurified substrates and can be used in green solvents (H2O, anisole) under ambient air, selectively yielding the anti-Markovnikov hydrosilylated products (yields up to >99%) at 70 °C using 2 mol% catalyst. MnBr(CO)5 was also successfully employed for the synthesis of cross-linked materials using dienes, carbonyl and epoxide containing substrates with low Mn loadings (0.3 mol%) at 70 °C under ambient air. [ABSTRACT FROM AUTHOR]

Investigation of catalytic hydrogenation of CO2 to CO via the reverse water-gas shift (RWGS) was undertaken using Ni/SiO2-based catalysts. Among the array of catalysts tested, the Ni/SiO2 catalyst derived from the reduction of silicalite-1-encapsulated, ligand-protected Ni2+ (Ni0.2@S-1-red) exhibited promising performance. This catalyst demonstrated a CO2 conversion rate approaching the equilibrium conversion of RWGS, a selectivity for CO exceeding 99%, and a high space time yield of CO (9.7 mol gNi -1 h-1). The outcomes observed can be attributed to several factors, such as the highly dispersed Ni0 and Niδ+ species, as well as the presence of bridging oxygen of the Ni-O-Si structure, on which CO2 can be adsorbed moderately. The moderately bonded CO2 on Ni0.2@S-1-red allows for the efficient desorption of its reduced intermediate, i.e. *CO, resulting in the generation of gaseous CO at a rapid rate, consequently preventing its deep hydrogenation to CH4. Complementary Density Functional Theory (DFT) calculations were performed and revealed that CO molecules have poor adsorption and higher adsorption energy on the Ni@S-1 surface compared to the S-1 surface. This supports the rapid desorption of *CO and the observed high selectivity of CO. Moreover, the structure-activity correlation analysis further supports the claim of Ni0.2@S-1-red as a promising RWGS catalyst. [ABSTRACT FROM AUTHOR]

Indirect CO2 hydrogenation to methanol and ethylene glycol is a green, efficient, and economical technique for converting CO2 into high-value chemicals to address the intractable environmental crisis caused by CO2 emissions. However, traditional methods for screening and optimizing catalysts in this process mainly depend on experience and repeated 'trial-and-error' experiments, which are resource-, time- and cost-consuming tasks. Therefore, this study developed a machine learning framework for predicting the conversion ratio of ethylene carbonate and the yield of methanol and ethylene glycol from the indirect CO2 hydrogenation technology to accelerate the catalyst screening and optimization processes. The initial dataset was visualized by conducting principal component analysis and improved to ensure sufficient information variables for the machine learning model to distinguish between catalyst types. After comparing the optimized results of three algorithms, the neural network with two hidden layers is the core of the machine learning model of the indirect CO2 hydrogenation process. It was then further optimized by a feature engineering method coupled with feature importance analysis and the Pearson correlation matrix. It indicates that the optimized neural network model has higher performance, especially in predicting ethylene carbonate conversion and product yields. Compared with other input features, the space velocity and hydrogen/ester ratio are the two most important factors affecting the conversion ratio of ethylene carbonate and the yield of methanol and ethylene glycol. Based on the results of the feature importance analysis, a multi-objective optimization model with a genetic algorithm was employed to screen the most suitable catalyst. Compared with other catalysts, more efforts should be devoted to the optimized xMoOx–Cu/SiO2 catalyst for the industrialization of indirect CO2 hydrogenation technology after experimental verification. [ABSTRACT FROM AUTHOR]

Hemoproteins have recently emerged as attractive biocatalysts for catalyzing carbene-mediated cyclopropanation, a synthetically valuable reaction not found in nature. In this study, we present a hemoglobin-catalyzed strategy for the highly stereoselective synthesis of nitrile-substituted cyclopropanes. This method offers efficiency and environmental friendliness by utilizing an asymmetric olefin cyclopropanation reaction catalyzed by wild-type Vitreoscilla hemoglobin in the presence of in situ generated diazoacetonitrile. A diverse range of nitrile-substituted cyclopropanes could be synthesized in water with exceptional stereoselectivity, achieving up to 99.9% de and ee and high turnover numbers of up to 3232. By employing this sustainable approach, not only can various chiral nitrile-substituted cyclopropanes be efficiently obtained, but also the practical application of hemoglobin in organic synthesis can be expanded. [ABSTRACT FROM AUTHOR]

The utilization of stimuli-responsive hydrogels as bifunctional catalysts for an aqueous sequential organic transformation to prepare chiral organic molecules is not only environmentally friendly, but also complements the synthetic limitations of mutually contradictory multistep reactions. However, finding a solution to the incompatible issue arising from complicated multicomponent cross-interactions in sequential transformations is a significant challenge. To address this issue, we have developed a core–shell-structured hydrogel as a site-isolated bifunctional catalyst. This catalyst features thermoresponsive poly(N-isopropylmethacrylamide) with a switching function via a reversible transition between its hydrogel and solution phases that perfectly matches a temperature-tuned base-catalyzed aldol condensation/oxa-Michael addition at 70 °C and the ruthenium-catalyzed dynamic kinetic resolution asymmetric transfer hydrogenation (DKR-ATH) process at 40 °C. As we envisioned, through the harmonization of the conflicting sequential reactions, this aldol condensation/oxa-Michael addition/DKR-ATH cascade process can be achieved by transitioning from being incompatible to compatible, enabling direct access to chiral chromanols with 1,3-positioned dual stereocenters from commercially available ortho-hydroxyl arylketones and aldehydes. Mechanistic investigations, which involve monitoring the cascade reaction and analyzing the deuterium-labeling experiments, reveal a domino-like aldol condensation/oxa-Michael addition/DKR-ATH sequential route comprising an initial aldol condensation/oxa-Michael addition followed by the subsequent DKR-ATH process. [ABSTRACT FROM AUTHOR]

Both polyoxometalates (POMs) and organic small molecular catalysts show excellent performance in chemical synthesis. The incorporation of nanoscale POMs and organocatalysts allows the full expression of their respective merits and enables elusive reactions to be achieved in one catalytic system. However, the covalent combination of such two components has been rarely explored. Here, we have successfully designed and synthesized a bifunctional nanomolecular catalyst L -Pro-Mn-Anderson by grafting L -proline onto an Mn-Anderson POM for the first time, and catalytic experiments show that L -Pro-Mn-Anderson can realize the one-pot alcohol oxidation/three-component reaction to synthesize two types of heterocyclic compounds (5-aryl-pyrimido[4,5-b]quinoline-dione derivatives and pyrazolo[3,4-b] pyridine derivatives) in high yields up to 97%. The detailed characterization of the catalyst and the catalytic mechanism has shown that L -Pro-Mn-Anderson exhibits synergistic effects that combine both organic and inorganic catalytic functions, and the covalent linkage improves the overall redox activity of the molecular catalyst. This study opens up a new way for the design and application of covalently combined organic–inorganic molecular catalysts toward de novo organic synthesis. [ABSTRACT FROM AUTHOR]

Biomass-derived fatty acids are essential feedstock for producing liquid fuels and value-added chemicals with significantly low CO2 footprints. Herein, Ti3C2Tx and ZnO–Ti3C2Tx catalysts were synthesized and demonstrated for the selective hydrodeoxygenation reaction (HDO) of methyl oleate (MO) as a model compound. The synthesized ZnO–Ti3C2Tx catalyst showed 100% conversion of MO with >90% selectivity for the HDO product (n-C18). In addition, the pure Ti3C2Tx demonstrated 100% conversion with a selectivity of 67% for n-C17 hydrocarbon via the decarboxylation route. The highest reduction of CO2 footprint is achieved at 280 °C and 30 bar H2 pressure under solvent-free conditions using ZnO–Ti3C2Tx. The catalyst is recyclable and reusable for five test cycles. The high catalytic selectivity of the ZnO–Ti3C2Tx catalyst towards HDO is attributed to the synergic effect of the Ti and ZnO active sites and the thermally stable structure. This study offers an efficient route for converting edible and non-edible vegetable oils to biofuels by controlling CO2 production. [ABSTRACT FROM AUTHOR]

The use of molecular oxygen is unquestionably the green path to the selective oxidation of alcohols to aldehyde and ketones. However, this reaction class poses safety problems associated with mixing oxygen with organic substrates. Continuous membrane reactors offer an attractive solution, owing to their ability to keep the oxygen phase separated from the liquid substrate, while controlling the dosing of oxygen during reaction. In this work, we demonstrate a slurry loop membrane reactor for continuous oxidations as well as hydrogenations. The catalyst slurry was circulated around a loop, to which a saturator containing a flat Teflon AF-2400 membrane was connected, along with a crossflow filter to keep the catalyst particles within the loop. Under a recycle flowrate 100 times higher than the inlet, the residence time distribution was found to be comparable to that of an ideal CSTR. A remarkably high kLa of 1.2 s−1 was achieved under a moderate specific power input of 2.4 kW m−3 during styrene hydrogenation. Continuous aerobic oxidations of various primary and secondary alcohols were carried out for 6–7 h at 90–120 °C and 2–6 bar, using a 1 wt% Au-Pd/TiO2 powder catalyst, leading to conversions between 17% and 75%. The reactor could also be operated in batch mode, achieving higher conversions, while scaled-up operations produced aldehyde yields of 0.4–19 g with only 88 mg of catalyst. Overall, the slurry loop membrane reactor provides significant advantages in terms of catalyst usage and process safety for aerobic oxidations. [ABSTRACT FROM AUTHOR]

In recent years, chemical recycling to monomer (CRM) has emerged as an advanced strategy to deal with post-consumer plastics. However, because it usually takes a long time to react at a relatively high temperature, CRM suffers from side reactions and energy consumption issues. In this work, a Brønsted–Lewis acid ionic liquid/polyhydroxy-compound system ([Et3NH][ZnCl3]/pentaerythritol) was developed as a bifunctional reagent for dissolving poly(p-dioxanone) (PPDO) and highly efficiently catalysing its CRM. In situ addition of the polyhydroxy-compound significantly prevented the formation of byproduct, i.e., cyclic PPDO, by converting it back to depolymerizable linear PPDO. Therefore, both the CRM efficiency and selectivity were obviously improved. At 160 °C, PPDO was almost fully depolymerized to the PDO monomer in only 8 minutes with 99.9% GC purity of yield. Moreover, [Et3NH][ZnCl3]/pentaerythritol could be reused at least 5 times without post-processing and its chemical structure and efficiency remained intact. According to the kinetic study, the activation energy of depolymerization was calculated to be 64.81 kJ mol−1, half lower than the traditional method. Based on NMR titration, the catalytic mechanism was discussed. Importantly, according to the assessment of the energy economy factor, environmental factor, and environmental energy impact factor, the strategy developed in this work is better than all of the related works in greenness. [ABSTRACT FROM AUTHOR]

The catalytic hydrolysis/alcoholysis of biomass carbohydrates into levulinic acid/levulinate esters (alkyl levulinates) as green biofuels and value-added chemicals holds great promise for achieving the goals of sustainable chemistry. Bifunctional catalysts with Brønsted- and Lewis-acidic sites have been widely reported to boost the efficiency of both processes. However, current understanding of the origin of the enhancement in alcoholic media is still in its infancy compared to that in aqueous media. Herein, we investigate the reaction process of glucose in methanol using a representative bifunctional catalyst (aluminum phosphotungstate) and its Brønsted-acid form (phosphotungstic acid), respectively. Isotopic labeling experiments were first applied to monitor the potential intermediates in glucose methanolysis. Coupling with mass spectrometric analysis and theoretical calculations, it has been revealed that Al3+ ions may accelerate the rate-limiting step by inducing ring opening of the key intermediate, methyl- D -glucopyranoside (MDGP), to D -glucose dimethyl acetal, rather than the prevalent speculation of facilitating the isomerization of MDGP to methyl fructoside. These findings refresh and reinforce our knowledge of the mechanism behind catalytically producing alkyl levulinates from biomass carbohydrates and provide a basis for the rational design of superior catalysts for biomass valorization. [ABSTRACT FROM AUTHOR]

A unique electrochemical four-component reaction of terminal alkynes, (thio)xanthenes, nitriles, and water has been established in the absence of any catalyst or external oxidant. This electrochemical reaction features high atom economy and mild conditions, affording oxazole derivatives in moderate to good yields. [ABSTRACT FROM AUTHOR]

Electricity-to-chemical production from a hybrid microbial–inorganic catalytic system relies upon biocompatible and efficient catalysts for hydrogen evolution reactions (HERs). Herein, metal-free nitrogen-doped carbon nanosheets (NC) with no metal leaching and little generation of reactive oxygen species were synthesized to develop an efficient hybrid catalytic system for converting CO2 to poly-β-hydroxybutyrate. A yield of 538 mg L−1 with an electricity-to-organic efficiency of 10.5% was obtained, which outcompetes most of the previous achievements. The coupling of NC with Ralstonia eutropha H16 reduced the HER overpotential by 200 mV. It was attributed to the doped N atoms facilitating the immobilization of bacteria on the catalysts to enhance hydrophilicity. Besides, the [NiFe]-hydrogenase from R. eutropha accelerates the desorption of H2 and may provide an effective HER catalytic center on the catalysts. This study reveals the synergistic interactions between metal-free catalysts and R. eutropha H16 to promote H2 production and CO2 conversion. [ABSTRACT FROM AUTHOR]

Herein we describe the syntheses of a series of molybdate and polyoxomolybdate ionic liquids (ILs), their full spectroscopic characterisation (FT-IR, 1H-, 13C-, 31P-, and 95Mo-NMR and ICP-MS), a comparison of their properties, and their applications as bifunctional catalysts for CO2 insertion into epoxides. The synthetic procedures to obtain ILs rely on anion exchange and acid–base reactions, including an innovative route for the synthesis of molybdate ionic liquids (Mo-ILs) using a halide-free organic IL precursor. The use of Mo-ILs as catalysts for CO2 fixation was investigated using 1,2-epoxyhexane as a model substrate. In the presence of 2.5 mol% of tetrabutylammonium molybdate, hexane carbonate was obtained in up to 86% yield at T = 120 °C, p0(CO2) = 30 bar in t = 9 h, under solventless conditions and without any added halide co-catalysts. The substrate scope was broadened to other 12 terminal and internal epoxides; moreover, the reaction was scaled up to 2 g of the substrate and catalyst recyclability was demonstrated up to 5 recycles. [ABSTRACT FROM AUTHOR]

The pursuit of hydrogen peroxide (H2O2) production via two-electron electrochemical oxygen reduction reaction (ORR) is hampered by the lack of high-performance electrocatalysts. In this work, a series of single metal (i.e., Fe, Co, Ni, and Cu) atom catalysts anchored into N-doped carbon nanosheets (NCNSs) are evaluated for H2O2 production at pH-universal electrolytes. The catalytic performance of the samples, including current density, H2O2 selectivity, turnover of frequency (TOF), and faradaic efficiency, are characterized by electrochemical measurements. The generation of H2O2 is monitored by a UV-vis spectrophotometer. Among the samples, Cu/NCNSs exhibits the best catalytic performance with a ring current density of 2.15 mA cm−2, TOF of 15.8 s−1 at 0.1 V vs. reversible hydrogen electrode, Tafel slope of 88 mV dec−1, and H2O2 selectivity of 100% at 0.57 V in alkaline media. Importantly, the Cu/NCNSs yields H2O2 selectivity of 81% at 0.05 V in acidic electrolytes. In contrast, Cu nanoparticles possess an inferior current density and much lower H2O2 selectivity via the 4e− ORR pathway. Further quantitative analysis of H2O2 demonstrates that the Cu/NCNSs catalyst has an H2O2 production rate of 5.1 mol gcatalyst−1 L−1 h−1 in alkaline media at 0.4 V, which is larger than those in acidic media (3.2 mol gcatalyst−1 L−1 h−1) and neutral media (2.2 mol gcatalyst−1 L−1 h−1) at −0.2 V. Such performance of Cu/NCNSs renders it as one of the best catalysts for H2O2 production. [ABSTRACT FROM AUTHOR]

Directly converting biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-bis(alkoxymethyl)furans (BAMFs) via a one-pot process in alcohol systems is a very important approach for the synthesis of high-quality biofuels; however, this approach is highly challenging because it simultaneously involves the cascading Meerwein–Ponndorf–Verley (MPV) reduction and etherification reactions. Thus, designing an acid–base bifunctional catalyst is extremely desirable. Herein, we employed a glucose-based carbonaceous solid acid as a cheap organic ligand to prepare a series of new-type sulfonated zirconium–carbon coordination catalysts (Zr-GC-SO3H-X) via a simple solvothermal self-assembly method. By regulating the usage proportion of zirconium ions and organic ligand, Zr-GC-SO3H-1.0, possessing a proper Lewis/Brønsted acid ratio as well as strong Lewis acid–base (Zr4+–O2−) and Brønsted acid (–SO3H) sites, showed the optimum acid–base synergistic effects, so it displayed the highest catalytic performance. When the one-pot reductive etherification (OPRE) of HMF was performed in isopropanol, 2,5-bis(isopropoxymethyl)furan (BIPMF) yield could reach 95.8% in 6 h at 180 °C. Additionally, the analysis results of reaction processes demonstrated that the MPV reduction reaction of HMF was much easier than its etherification reaction in the presence of Zr-GC-SO3H-1.0, so initially forming 2,5-bis(hydroxymethyl)furan (BHMF) and then forming 2-hydroxymethyl-5-(isopropoxymethyl)furan (HIPMF) were the predominant reaction pathway for the OPRE of HMF to BIPMF. More significantly, Zr-GC-SO3H-1.0 also exhibited excellent universality and catalyzed the high-yield synthesis of various BAMFs in ethanol, n-propanol, n-butanol and sec-butanol. Conclusively, this work provided momentous references to construct high-efficiency catalysts for the OPRE of HMF. [ABSTRACT FROM AUTHOR]