Catalyst Solvent Research Articles

Enhancing the selective catalytic oxidation of lignocellulosic biomass to formic acid using hydrogen peroxide and a reusable MgAl hydrotalcite-derived as a catalyst in a green solvent

Biofuels or liquid fuels derived from natural matter, are one of the most intriguing yet divisive alternatives for petroleum-based fuels. The most common approach to produce biofuels is to transform plant sugars and other carbohydrates into oxygen-deficient chemicals. A growing relevance has been devoted in the direct synthesis of platform molecules from biomass resources, using one-pot or cascade techniques via adequate catalytic system tuning and improvement of the reaction conditions which have merged as a beneficial strategy from an economic and ecological standpoint. In a similar vein, the major objective of this contribution was to investigate and enhance the conditions for a selective oxidation of lignocellulosic biomass-derived cellulose to yield formic acid (FA), the latter is one of the most coveted liquid hydrogen carriers and among the key compounds used in the pharmaceutical, cosmetic, and leather industries. Both oxidizing aqueous hydrogen peroxide and calcined heterogeneous hydrotalcite catalyst have been employed at an atmospheric pressure for this purpose. The effect of reaction time, temperature, amount of catalyst and oxidant on the product's yield and selectivity have been investigated. The oxidation of a plant-derived cellulosic fiber at 70 °C using an H2O2 excess (7 mmol) provided an impressive result with a high yield and TON of 61.0 %, 12.30 respectively, the latter was confirmed to be relatively close to the one from the oxidation of pure cellulose. Furthermore, the reusability of the catalyst has also been studied which was demonstrated to result in the same yields for one reuse and 3 recycles.

Catalytic hydrothermal liquefaction of Azolla filiculoides into hydrocarbon rich bio-oil over a nickel catalyst in supercritical ethanol

Hydrothermal liquefaction (HTL) is one of the most promising thermochemical techniques for converting wet biomass into crude oil-like products (bio-oil). In this study, Catalytic hydrothermal liquefaction of Azolla filiculoides (AZ) was performed over a various loading of nickel (Ni) on magnesium oxide (MgO) catalyst for the higher and quality bio-oil production. The key operating parameters such as temperature, reaction holding time, amount of Ni on MgO supports catalyst, and reaction solvents were investigated in the presence of a hydrogen environment. There was a 12.8 wt% increase in bio-oil yield and a 6.3 wt% decrease in biochar yield with addition of 15 wt% Ni catalysts compared to the non-catalytic reaction bio-oil yield (44.0 wt%). Results confirmed the highest total bio-oil yield of 56.8 wt% was attained at 280 °C with the catalyst amount of 15 wt% at a residence time of 45 min. Gas chromatography-mass spectrometry (GC-MS), FT-IR, CHNS, TGA, and NMR analyses were performed on the bio-oil, identifying 32.8 % long-chain hydrocarbons (C12-C16) along with small amounts of alcohols, alkanes, and esters. The boiling point distribution revealed that bio-oil produced using the Ni/MgO catalyst contained a significantly higher proportion of diesel-range hydrocarbons (42.4 %). Furthermore, the bio-oil yield under ethanol solvent and Ni catalysts showed higher heating value (HHV) 42.2 MJ/kg. Overall in the presence of Ni hydrogenation efficient catalysts on MgO in the liquefaction reaction promoted the deoxygenation and hydrogenation reaction.

A New Route for the Synthesis of Trichloromethyl-1H-Benzo[d]imidazole and (1,2,3- Triazol)-1H-Benzo[d]imidazole Derivatives via Copper-Catalyzed N-Arylation and Huisgen Reactions

Abstract: In this study, functionalized 2-(trichloromethyl)-1H-benzo[d]imidazole derivative with good yields was synthesized using a copper-catalyzed N-arylation reaction of 2-iodoaniline and trichloroacetonitrile. This reaction was performed by employing the catalytic value of copper (I) and 1,10-phenanthroline as the ligand in tetrahydrofuran solvent at 23°C. In the following, the reaction of the final product with phenylacetylene and sodium azide (Huisgen reaction) using the copper catalyst in water solvent at 23°C led to the synthesis of new (1,2,3-triazol)-1H-benzo[d]imidazole derivatives with the principles of green chemistry and suitable efficiency. The availability of raw materials and suitable catalysts, mild reaction conditions, and easy purification are among the advantages of this method for the synthesis of various multi-substituted benzo[d]imidazole and 1,2,3-triazole derivatives.

Ultra-Stretchable Composite Organohydrogels Polymerized Based on MXene@Tannic Acid-Ag Autocatalytic System for Highly Sensitive Wearable Sensors.

Conductive hydrogels have attracted widespread attention in the fields of biomedicine and health monitoring. However, their practical application is severely hindered by the lengthy and energy-intensive polymerization process and weak mechanical properties. Here, a rapid polymerization method of polyacrylic acid/gelatin double-network organohydrogel is designed by integrating tannic acid (TA) and Ag nanoparticles on conductive MXene nanosheets as catalyst in a binary solvent of water and glycerol, requiring no external energy input. The synergistic effect of TA and Ag NPs maintains the dynamic redox activity of phenol and quinone within the system, enhancing the efficiency of ammonium persulfate to generate radicals, leading to polymerization within 10min. Also, ternary composite MXene@TA-Ag can act as conductive agents, enhanced fillers, adhesion promoters, and antibacterial agents of organohydrogels, granting them excellent multi-functionality. The organohydrogels exhibit excellent stretchability (1740%) and high tensile strength (184kPa). The strain sensors based on the organohydrogels exhibit ultrahigh sensitivity (GF=3.86), low detection limit (0.1%), and excellent stability (>1000 cycles, >7 days). These sensors can monitor the human limb movements, respiratory and vocal cord vibration, as well as various levels of arteries. Therefore, this organohydrogel holds potential for applications in fields such as human health monitoring and speech recognition.

Metal-Free Switchable Chemo- and Regioselective Alkylation of Oxindoles Using Secondary Alcohols.

In this study, we have disclosed N-alkylation and C-alkylation reactions of 2-oxindoles with secondary alcohols. Interestingly, these chemoselective reactions are tunable by changing the reaction conditions. Utilization of protic solvent and Brønsted acid catalyst afforded C-alkylation, whereas, aprotic solvent and Lewis acid catalyst afforded N-alkylation of 2-oxindoles in good to excellent yields. Regioselectivity is achieved by protecting the N-center of the oxindole and C5 alkylated product is furnished exclusively. This protocol is notable because it demonstrates functionalization at the C7 position of oxindole without the need for any directing group at the N-center. Further, a new protocol has been reported for C-H oxygenation at the benzylic position of one of the C5 alkylated derivative.

New insight into dehydration reaction of xylose and hemicellulose to furfural over dual-acid deep eutectic solvent catalysts

Furfural (FF) is one of the most important platform molecules in the conversion of xylose and hemicellulose. However, the conversions of xylose and hemicellulose to FF with Brønsted acid (B-acid) and Lewis acid (L-acid) as catalysts suffer from harsh reaction conditions and low yield, respectively. B-L acid deep eutectic solvents (B-L ADESs), which consist of both B-acid and L-acid, were designed to catalyze the reaction of xylose and hemicellulose to FF under mild conditions. Surprisingly, B-L ADES exhibits excellent catalytic activity for the preparation of FF from xylose and hemicellulose, which exceeds most results reported thus far. Furthermore, it is proved from the kinetics perspective and density functional theory (DFT) calculations that the synergistic action of B-L acids has lower activation energy and higher FF yield than that of B-acid and L-acid alone. The strategy of B-L acid combination provides a theoretical basis for the subsequent design of sustainable catalysts.

Synthesis of spiroindoline derivatives and biphenyl compounds in green solvent via a “capture–release” mechanism using modified polyacrylonitrile fiber as a catalyst

Green synthesis of critical bioactive molecules and fine chemicals is attracting increasing interest. This study investigates the use of two distinct functionalized polyacrylonitrile (PAN) fibers (PANEDBPF and PANEDBP-Pd0F) as effective catalysts in a green solvent comprising ethanol and water. Firstly, a PAN fiber was modified using 2-(diphenylphosphino) ethylamine, a strongly nucleophilic phosphine compound, to obtain PANEDBPF. Spiroindoline derivatives were obtained in 98 % yields when the reaction was conducted using 5 mol% of PANEDBPF as the catalyst at 70 °C for 30 min. Next, we loaded PdNPs onto PANEDBPF to obtain PANEDBP-Pd0F. When the Suzuki coupling reaction was conducted at room temperature (25 °C) using 0.5 mol% of PANEDBP-Pd0F, the products were obtained in an extremely high yield of 99 %. Additionally, the unique enrichment of the substrate by the functionalized fibers during the reaction and the subsequent release of the product from the microenvironment conform to the “capture–release” reaction mode of catalysis. Both PANEDBPF and PANEDBP-Pd0F demonstrated good gram-scale amplification, repeatability, catalytic activity, and stability. Hence, they are highly promising candidates for green chemistry applications.

Oxidative Upcycling of Polyethylene to Long Chain Diacid over Co-MCM-41 Catalyst.

Plastic pollution is an emerging global threat due to lack of effective methods for transforming waste plastics into useful resources. Here, we demonstrate a direct oxidative upcycling of polyethylene into high-value and high-volume saturated dicarboxylic acids in high carbon yield of 85.9 % in which the carbon yield of long chain dicarboxylic (C10-C20) acids can reach 58.9% over cobalt-doped MCM-41 molecular sieves, in the absence of any solvent or precious metal catalyst. The distribution of the dicarboxylic acids can be controllably adjusted from short-chain (C4-C10) to long-chain ones (C10-C20) through changing cobalt loading of MCM-41 under nanoconfinement. Highly and sparsely dispersed cobalt along with confined space of mesoporous structure enables complete degradation of polyethylene and high selectivity of dicarboxylic acid in mild condition. So far, this is the first report on highly selective one-step preparation of long chain dicarboxylic acids. The approach provides an attractive solution to tackle plastic pollution and a promising alternative route to long chain diacids.

Oxidative Upcycling of Polyethylene to Long Chain Diacid over Co‐MCM‐41 Catalyst

AbstractPlastic pollution is an emerging global threat due to lack of effective methods for transforming waste plastics into useful resources. Here, we demonstrate a direct oxidative upcycling of polyethylene into high‐value and high‐volume saturated dicarboxylic acids in high carbon yield of 85.9 % in which the carbon yield of long chain dicarboxylic (C10‐C20) acids can reach 58.9% over cobalt‐doped MCM‐41 molecular sieves, in the absence of any solvent or precious metal catalyst. The distribution of the dicarboxylic acids can be controllably adjusted from short‐chain (C4‐C10) to long‐chain ones (C10‐C20) through changing cobalt loading of MCM‐41 under nanoconfinement. Highly and sparsely dispersed cobalt along with confined space of mesoporous structure enables complete degradation of polyethylene and high selectivity of dicarboxylic acid in mild condition. So far, this is the first report on highly selective one‐step preparation of long chain dicarboxylic acids. The approach provides an attractive solution to tackle plastic pollution and a promising alternative route to long chain diacids.

Boosting catalytic performance of Amberlyst‐15 by modulating surface properties for synthesis of 5-hydroxymethylfurfural from high-concentration fructose

The large-scale production of 5-hydroxymethylfurfural (HMF), a “sleeping giant” in sustainable chemistry, is frequently hampered by the severe formation of humins during the acid-catalyzed dehydration of high-concentration fructose. In this work, we demonstrate that the HMF yield could be remarkably enhanced by boosting the catalytic performance of a commercially used Amberlyst-15 solid acid organocatalyst, wherein the formation of humins could be effectively inhibited. We show that the modification of Amberlyst-15 with a typical cationic surfactant (i.e., cetyltrimethylammonium bromide (CTAB)) via charge interaction between sulfonic acid groups and quaternary ammonium cations led to an improved surface hydrophobicity and a reduced Brønsted acid density on the modified catalyst, thereby contributing to a complete suppression of HMF rehydration and remarkable suppression of humin formation via paths of both etherification-dehydration-condensation and degradative-condensation of fructose and/or HMF. As a result, the catalytic conversion of fructose over the CTAB-modified Amberlyst-15 catalyst in a low-boiling mixed solvent composed of 1,4-dioxane and H2O at 140 °C within 2 h led to high HMF yields in range of 53.3 ∼ 63.1 mol% in converting high-concentration fructose (10.0 ∼ 50.0 wt%), wherein an average enhancement of 20 mol% in product yield was achieved when compared with that over un-modified Amberlyst-15. Moreover, the adsorption of humins on solid catalyst was significantly reduced due to the enhanced surface hydrophobicity and alleviated formation of humins, which accounted for a stable catalytic performance of the modified Amberlyst-15 catalyst for at least five runs. This work highlights the rational adjustment of the surface wettability of a commercial solid acid catalyst to suppress the undesired humin formation for future HMF biorefinery.

Efficient Hydrochlorination of Acetylene by the Ag–Ru Bimetallic Catalyst in a Deep Eutectic Solvent

Efficient Hydrochlorination of Acetylene by the Ag–Ru Bimetallic Catalyst in a Deep Eutectic Solvent

Performance assessment of novel catalytic spouted-bed vapor jet flow heat exchanger in amine-based carbon capture process

This study introduced a spouted bed and jet flow catalytic heat exchanger (SBJ-EX). This novel non-agitated technology can potentially integrate with a conventional desorption column to enhance heat transfer and CO2 desorption performance in amine-based post-combustion carbon capture systems. As its first research in the carbon capture field, this work experimentally evaluated key factors including overall heat transfer coefficient, logarithmic mean temperature difference, temperature distribution along the reactor, and cyclic loading under varied parameters such as inlet temperature of the heating oil, inlet solvent temperature, rich CO2 loadings, and mass of catalysts to simulate real-world operating conditions using benchmark MEA solvent and solid acid catalyst HZSM-5. Compared to conventional plate heat exchangers, the SBJ-EX demonstrated over a 70 % enhancement in heat transfer performance due to its effective overall heat transfer coefficient. It also exhibited impressive CO2 desorption performance even at lower temperatures with sufficient catalysts. Unlike agitated-type heat exchangers, the SBJ-EX could minimize catalyst attrition and offer more excellent stability. In contrast to fixed-bed catalyst desorbed columns, this equipment offered a more compact design for quicker and simpler catalyst replacement to reduce downtime for operators significantly. The SBJ-EX can also function as an optional backup or add-on unit to provide operators with flexibility. This work further discussed advantages and challenges of the SBJ-EX operation. This work enriched the future research outlook for this technology, and contributed a commercially viable approach to catalysts in carbon capture processes.

Recent advances in polyethylene glycol as a dual‐functional agent in heterocycle synthesis: Solvent and catalyst

AbstractReactant solubility, which dictates achievable concentrations, and the stability of reaction intermediates (excited states), solvents modulate the potential energy landscape and influence reaction rates. Consequently, solvent selection is pivotal in optimizing process productivity, economic feasibility, and environmental footprint. At present, organic synthesis pivots around the idea of sustainability. In particular, PEG‐400, a popular solvent and phase transfer catalyst, is considered greener as it can be reused several times without significant loss in its catalytic activity, which checks the box regarding sustainability. This review highlights the emerging potential of Polyethylene Glycol 400 (PEG‐400) as a dual‐threat agent in sustainable organic synthesis. We explore its efficacy as a catalyst, promoting various reactions under mild conditions and often eliminating the need for traditional metal catalysts. Additionally, PEG‐400's role as a green solvent is addressed, emphasizing its biodegradability, low toxicity, and ability to facilitate reactions without hazardous Volatile Organic Compounds (VOCs). The review examines recent research on PEG‐400 mediated reactions, showcasing its effectiveness in diverse transformations, thus exploring the potential of PEG 400 as a facilitator for heterocycle synthesis in both multicomponent reactions and stepwise approaches. It identifies exciting research directions that promise to expand the boundaries of polymer‐based solvents in heterocyclic chemistry.

Asymmetric Aldol Reactions Catalyzed by Polymeric Self-Assembly with Side-Chain Dipeptide Pendants.

To explore the role of proline amide moieties in polymer-supported organocatalysts, side-chain l-proline-l-alanine (Pro-Ala) dipeptide-containing block copolymers were synthesized, and their catalytic potential for the aldol reaction was explored. The dipeptide monomer (Boc-Pro-Ala-HEMA) was polymerized to prepare block copolymers in the presence of hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) and hydrophobic poly(methyl methacrylate) (PMMA) macro-chain transfer agents. Boc group expulsion from the block copolymers produced double hydrophilic PPEGMA-b-P(Pro-Ala-HEMA) (1b) and amphiphilic PMMA-b-P(Pro-Ala-HEMA) (1c) polymers. The solution behaviors of the polymers were studied by various physical techniques, which showed the formation of self-assembled aggregates of 1c in water and N,N-dimethylformamide (DMF)/water solvent mixtures. These polymers are used as organocatalysts during the aldol reaction of cyclohexanone and 4-nitrobenzaldehyde in different solvent polarities, catalyst loadings, temperatures, and reaction times. This work emphasizes superior catalytic activity of 1c at lower catalyst loadings (5%) while maintaining high conversion (95%) and enantioselectivity (94%) across multiple recycling cycles in DMF/water at a 3:1 ratio (v/v).

Niobium-based single-atom catalyst promoted fractionation of lignocellulose in choline chloride-lactic acid deep eutectic solvent

Pretreatment is the key step to convert lignocelluloses to sustainable biofuels, biochemicals or biomaterials. In this study, a green pretreatment method based on choline chloride-lactic acid deep eutectic solvent (ChCl-LA) and niobium-based single-atom catalyst (Nb/CN) was developed for the fractionation of corn straw and further enzymatic hydrolysis of cellulose. With this strategy, significant lignin removal of 96.5 % could be achieved when corn straw was pretreated by ChCl-LA (1:2) DES over Nb/CN under 120 °C for 6 h. Enzymatic hydrolysis of the cellulose-enriched fraction (CEF) presented high glucose yield of 92.7 % and xylose yield of 67.5 %. In-depth investigations verified that the high yields of fractions and monosaccharides was attributed to the preliminary fractionation by DES and the deep fractionation by Nb/CN. Significantly, compared to other reported soluble catalysts, the synthesized single-atom catalyst displayed excellent reusability by simple filtration and enzymatic hydrolysis. The recyclability experiments showed that the combination of ChCl-LA DES and Nb/CN could be repeated at least three times for corn straw fractionation, moreover, the combination displayed remarkable feedstock adaptability.

Palladium Complexes Derived from Waste as Catalysts for C-H Functionalisation and C-N Bond Formation

Three-way catalysts (TWCs) are widely used in vehicles to convert the exhaust emissions from internal combustion engines into less toxic pollutants. After around 8–10 years of use, the declining catalytic activity of TWCs causes them to need replacing, leading to the generation of substantial amounts of spent TWC material containing precious metals, including palladium. It has previously been reported that [NnBu4]2[Pd2I6] is obtained in high yield and purity from model TWC material using a simple, inexpensive and mild reaction based on tetrabutylammonium iodide in the presence of iodine. In this contribution, it is shown that, through a simple ligand exchange reaction, this dimeric recovery complex can be converted into PdI2(dppf) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), which is a direct analogue of a commonly used catalyst, PdCl2(dppf). [NnBu4]2[Pd2I6] displayed high catalytic activity in the oxidative functionalisation of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of an oxidant, PhI(OAc)2. Near-quantitative conversions to the desired product were obtained using a catalyst recovered from waste under milder conditions (50 °C, 1–2 mol% Pd loading) and shorter reaction times (2 h) than those typically used in the literature. The [NnBu4]2[Pd2I6] catalyst could also be recovered and re-used multiple times after the reaction, providing additional sustainability benefits. Both [NnBu4]2[Pd2I6] and PdI2(dppf) were also found to be active in Buchwald–Hartwig amination reactions, and their performance was optimised through a Design of Experiments (DoE) study. The optimised conditions for this waste-derived palladium catalyst (1–2 mol% Pd loading, 3–6 mol% of dppf) in a bioderived solvent, cyclopentyl methyl ether (CPME), offer a more sustainable approach to C-N bond formation than comparable amination protocols.

Mechanism of initiation of ethylene cationic polymerization in the presence of an aluminum chloride aquacomplex in heptane with a stoichiometric composition of 1:1:1:2 at the quantum level

In this paper, the mechanism of ethylene initiation in the presence of an aluminum chloride – water catalyst in a heptane solvent of stoichiometric composition 1:1:1:2 was studied using the ab initio RHF theoretical quantum chemical method. The activation energy and thermal effect of this reaction were obtained. These data can be useful for further research in the field of cationic polymerization, and can also be used in the development of new technological processes of polyethylene with specified physicochemical properties characteristic of fiber optics.

Sonocatalysis green synthesis of indeno[1,2‐b]indolone derivatives using CuFe2O4@CS‐SB nanocomposite as a reusable catalyst under mild conditions

In this literature, the synthesis of indeno[1,2‐b]indolone from starting materials of ninhydrin, derivatives of aniline, and dimedone by using copper ferrite anchored to chitosan bearing Schiff base (CuFe2O4@CS‐SB) as a catalyst in water solvent under ultrasound irradiation was described. This catalyst was designed, fabricated, and characterized by the FT‐IR, 1H NMR, XRD, SEM, TGA, mapping scan, EDX, and BET techniques. This prepared acidic, effective heterogeneous catalyst catalyzed green synthesis of indeno‐indolone derivatives in a very short reaction times between 1 and 7 min with excellent yields between 95% and 99%. Also, the FT‐IR, 1H NMR, and melting point analyses are used to identify the synthesis of the indolones as organic products.

The Emerging Role of Polyethylene Glycol-Water (PEG-H2O) as the Benign Mixed Solvent System in Organic Synthesis

Abstract: Polyethylene glycol (PEG) has become a popular solvent and green catalyst for a variety of chemical reactions. It is a stable and biodegradable polymeric catalyst used in organic synthesis because it may be recycled numerous times without significantly losing its catalytic activity. Recently, the use of PEG-H2O mixed solvent systems in organic synthesis has gained popularity. This article presents an overview of PEG-H2O solvent system-mediated organic reactions, with a main focus on the importance of the solvent system. The study also focuses on recent developments in the PEG-H2O solvent system-mediated synthesis of a number of heterocy-clic compounds. Important characteristics of these PEG-H2O solvent systems include high atom economies, gentle reaction conditions, faster reaction rates, readily isolated side products and high yields. Results from various reactions showed that the choice of proper ratio of PEG: H2O solvent system plays a key role in product yields.

Synthesizing Hypercrosslinked Polymers with Deep Eutectic Solvents to Enhance CO2 /N2 Selectivity.

Hypercrosslinked polymers (HCPs) are widely used in ion exchange, water purification, and gas separation. However, HCP synthesis typically requires hazardous halogenated solvents e. g., dichloroethane, dichloromethane and chloroform which are toxic to human health and environment. Herein we hypothesize that the use of halogenated solvents in HCP synthesis can be overcome with deep eutectic solvents (DES) comprising metal halides-FeCl3 , ZnCl2 that can act as both the solvent hydrogen bond donor and catalyst for polymer crosslinking via Friedel Crafts alkylation. We validated our hypothesis by synthesizing HCPs in DESs via internal and external crosslinking strategies. [ChCl][ZnCl2 ]2 and [ChCl][FeCl3 ]2 was more suitable for internal and external hypercrosslinking, respectively. The specific surface areas of HCPs synthesized in DES were 20-60 % lower than those from halogenated solvents, but their CO2 /N2 selectivities were up to 453 % higher (CO2 /N2 selectivity of poly-α,α'-dichloro-p-xylene synthesized in [ChCl][ZnCl2 ]2 via internal crosslinking reached a value of 105). This was attributed to the narrower pore size distributions of HCPs synthesized in DESs.