Subsequent Reaction Cycles Research Articles

Rapidly solidified Al-Cu-Co quasicrystalline alloy: microstructure and catalytic properties

This study presents the characterisation and evaluation of the catalytic potential of an alloy with a composition referring to the quasicrystal from the Al-Cu-Co system. The material was synthesised through a melt-spinning process, providing rapid solidification conditions and a favourable material form of thin ribbons. Microstructural and chemical analyses were performed using scanning electron microscopy, X-ray diffraction and transmission electron microscopy methods. The obtained results confirmed the presence of a major phase which was a decagonal quasicrystal in the form of globular grains and additional crystalline phases occurring along the grain boundaries. The catalytic potential of the materials was explored using phenylacetylene hydrogenation. The catalyst, obtained by pulverising the ribbons, demonstrated catalytic activity with over 40% phenylacetylene conversion and selectivity exceeding 60% for styrene production under mild reaction conditions. The recovered catalyst displayed a stable phase composition, as confirmed by X-ray diffraction, and unchanged morphology, indicating the possibility of catalyst reuse for subsequent reaction cycles. The presented results provide insight into the experimental verification of the catalytic properties of the developed environmentally friendly catalysts.

Covalent bonding of N-hydroxyphthalimide on mesoporous silica for catalytic aerobic oxidation of p-xylene at atmospheric pressure.

The surface of SBA-15 mesoporous silica was modified by N-hydroxyphthalimide (NHPI) moieties acting as immobilized active species for aerobic oxidation of alkylaromatic hydrocarbons. The incorporation was carried out by four original approaches: the grafting-from and grafting-onto techniques, using the presence of surface silanols enabling the formation of particularly stable O-Si-C bonds between the silica support and the organic modifier. The strategies involving the Heck coupling led to the formation of NHPI groups separated from the SiO2 surface by a vinyl linker, while one of the developed modification paths based on the grafting of an appropriate organosilane coupling agent resulted in the active phase devoid of this structural element. The successful course of the synthesis was verified by FTIR and 1H NMR measurements. Furthermore, the formed materials were examined in terms of their chemical composition (elemental analysis, thermal analysis), structure of surface groups (13C NMR, XPS), porosity (low-temperature N2 adsorption), and tested as catalysts in the aerobic oxidation of p-xylene at atmospheric pressure. The highest conversion and selectivity to p-toluic acid were achieved using the catalyst with enhanced availability of non-hydrolyzed NHPI groups in the pore system. The catalytic stability of the material was additionally confirmed in several subsequent reaction cycles.

Label-free and sensitive fluorescent sensing of ten-eleven translocation enzyme via cascaded recycling signal amplifications

The sensitive detection of ten-eleven translocation (TET) dioxygenase is of significance for understanding the demethylation mechanism of 5-methylocytosine (5mC), which is responsible for a wide range of biological functions that can affect gene expression in eukaryotic species. Here, a non-label and sensitive fluorescence biosensing method for TET assay using TET1 as the model target molecule is established on the basis of target-triggered Mg2+-dependent DNAzyme and catalytic hairpin assembly (CHA)-mediated multiple signal amplification cascades. 5mC sites in the hairpin DNA probe are first oxidized by TET1 into 5-carboxycytosine, which are further reduced by pyridine borane into dihydrouracil, followed by its recognition and cleavage by the USER enzyme to liberate active DNAzyme and G-quadruplex sequences from the probe. The DNAzyme further cyclically cleaves the substrate hairpins to trigger subsequent CHA reaction and DNAzyme cleavage cycles for yielding many G-quadruplex strands. Thioflavin T dye then intercalates into G-quadruplexes to cause a magnificent increase of fluorescence for high sensitivity assay of TET1 with 47 fM detection limit. And, application of this method for TET1 monitoring in diluted serum has also been confirmed.

Blast furnace gas decarbonisation through Calcium Assisted Steel‐mill Off‐gas Hydrogen production. Experimental and modelling approach

The Calcium Assisted Steel-mill Off-gas Hydrogen production process (CASOH) is able to upgrade and decarbonise blast furnace gases (BFG), which is the main source of CO2 emissions in integrated steel making plants. The three main reaction stages of the process (i.e. H2 production via calcium-assisted water-gas-shift of BFG, Cu oxidation and CO2 sorbent regeneration) have been investigated in a lab-scale fixed bed reactor, using readily available functional materials (i.e. a commercial Cu-based catalyst and calcined limestone for the CO2 capture). The reactivity and stability of the materials have been studied after multiple cycles resembling the operating conditions expected in a TRL7 CASOH pilot plant under construction. A one-dimensional reactor model has been developed to simulate in detail the CASOH process and successfully validated with the experimental results obtained in the packed-bed reactor. Synthetic BFG mixed with steam has been converted into a product gas containing up to 40 vol% of H2 in N2 during the CASOH stage at atmospheric pressure and average temperatures in the bed around 650 ºC. During the Cu oxidation stage, the O2 contained in inlet air has been completely converted leading to moderate temperatures in the oxidation front (i.e. around 800 ºC). The oxidation at 4 bar has minimized the CO2 leakage during this stage. Finally, the reduction of CuO with simulated BFG and CH4 has produced in-situ sufficient heat to partially calcine at temperatures around 880ºC the CaCO3 present in the reactor leaving the solids ready for subsequent reaction cycles, while a CO2-rich gas is produced. The experimental and modelling results obtained in this work will be used to firstly design the experimental campaigns at the TRL7 CASOH pilot, and subsequently to interpret and scale up the pilot results using the validated model.

Light-controlled enzymatic synthesis of γ-CD using a recyclable azobenzene template.

Cyclodextrins (CDs) are important molecular hosts for hydrophobic guests in water and extensively employed in the pharmaceutical, food and cosmetic industries to encapsulate drugs, flavours and aromas. Compared with α- and β-CD, the wide-scale use of γ-CD is currently limited due to costly production processes. We show how the yield of γ-CD in the enzymatic synthesis of CDs can be increased 5-fold by adding a tetra-ortho-isopropoxy-substituted azobenzene template irradiated at 625 nm (to obtain the cis-(Z)-isomer) to direct the synthesis. Following the enzymatic reaction, the template can then be readily recovered from the product mixture for use in subsequent reaction cycles. Heating induces thermal cis-(Z) to trans-(E) relaxation and consequent dissociation from γ-CD whereupon the template can then be precipitated by acidification. For this study we designed and synthesised a set of three water-soluble azobenzene templates with different ortho-substituents and characterised their photoswitching behaviour using UV/vis and NMR spectroscopy. The templates were tested in cyclodextrin glucanotransferase-mediated dynamic combinatorial libraries (DCLs) of cyclodextrins while irradiating at different wavelengths to control the cis/trans ratios. To rationalise the behaviour of the DCLs, NMR titrations were carried out to investigate the binding interactions between α-, β- and γ-CD and the cis and trans isomers of each template.

Hydrolyzed Arabic gum-grafted-polyacrylonitrile@ zinc ferrite nanocomposite as an efficient biocatalyst for the synthesis of pyranopyrazoles derivatives

A catalytic methodology for the effective synthesis of pyrazolopyrazole derivatives using a combination of hydrolyzed Arabic gum-g-polyacrylonitrile/ZnFe2O4 (Hyd AG-g-PAN/ZnFe2O4) catalyst, malononitrile, and aromatic aldehyde, hydrazine hydrate, and ethyl acetoacetate is described. This protocol relies on the use of environment-friendly heterogeneous catalyst based on zinc ferrite magnetic particles in combination with Arabic gum (AG) as the backbone, N, N methylene bisacrylamide (MBA) as a crosslinking agent, ammonium persulfate (APS) as an initiator, and alkaline solution for hydrolyzation. This bio-based catalyst with a soft three-dimensional cross-linked framework contains distinct acidic and basic sites and could be applied as a powerful catalyst for the one-pot synthesis of pyranopyrazoles derivatives. Using an external magnet, the superparamagnetic nanocomposite could be easily separated. Furthermore, the catalyst can well be utilized at least six times in subsequent reaction cycles before losing its activity. FT-IR, EDX, TGA, FESEM, VSM, and XRD methods were used to characterize the produced catalyst. Taking 0.01 g of catalyst at 80 °C in a green solvent of water/ethanol, the greatest output of dihydropyrano [2,3-c] pyrazole was 96% in 15 min. A simple technique, short reaction time, high yield, and the catalyst's reusability and stability are just a few of the study's advantages.

Evaluation and kinetic study of alkaline ionic liquid for biodiesel production through transesterification of sunflower oil

Biodiesel production is performed in the industry by alkaline transesterification of oils with a low amount of free fatty acids. In order to reduce the disposal of conventional catalysts used industrially, ionic liquids (ILs) have been studied to be applied as catalysts in transesterification since they can be recovered and reused in subsequent reaction cycles. In this work, the ionic liquid choline hydroxide (ChOH) was successfully applied as a catalyst for the transesterification reaction of triacylglycerols present in sunflower oil with methanol. A kinetic modeling study under the specific conditions of 2 wt% catalyst dosage, 1:10 oil/methanol molar ratio, for 0–120 min at 35–65 ℃ was conducted, and liquid–liquid extraction with water/butanol was evaluated as a process to recover the IL. A 95.0% ester yield content was achieved in this work for a short reaction time (30 min). Furthermore, the results of the kinetic study demonstrated that a first-order model was the best fit for the reaction with a rate constant (k) estimated as 0.1182 min−1 and activation energy (Ea) of 13.64 kJ/mol. For the tested conditions, the complete recovery of the IL using liquid–liquid extraction did not occur since it is noted the presence of ChOH in both phases.

Bifunctional nano-catalyst produced from palm kernel shell via hydrothermal-assisted carbonization for biodiesel production from waste cooking oil

A highly mesoporous activated carbon derived from palm kernel shell was successfully prepared by hydrothermal-assisted carbonization (HTC) by improving the degradation of lignocellulosic composition and increase the porous texture of carbon structure. Additional NaOH treatment increased the surface area of the catalyst which enhanced the loading of the active site. Further impregnation of HTC based activated carbon with K2CO3 and CuO via wet impregnation provided bifunctional characteristics suitable for simultaneous esterification and transesterification processes. The physicochemical properties of the prepared catalysts were conducted through the state-of-the-art techniques including N2 adsorption-desorption analysis, functional group determination, surface morphology study, electron dispersive x-ray mapping, elemental distribution analysis, amount of basicity and acidity strength and thermal degradation behavior analysis. The investigation found that the chemical treatment with NaOH significantly increased the surface area from 3.57 to 3368.60 m2/g and impregnation with K2CO3 and CuO offered higher amount of basicity of 5.73 mmol/g and acidity of 1.48 mmol/g, respectively. These properties enhanced the simultaneous esterification-transesterification of waste cooking oil to biodiesel. The catalytic study produced 95.36 ± 1.4% of biodiesel over 4 wt% of PKSHAC-K2CO3(20%)CuO(5%) catalyst, 12:1 of methanol to oil molar ratio, reaction temperature of 70 °C for duration of 2 h. Meanwhile, the catalyst can be employed for five subsequent reaction cycles with FAME yield of 82.5 ± 2.5%. Thus, the synthesized bifunctional nanocatalyst supported on the HTC based activated carbon has been validated as an efficient catalyst for biodiesel production.

SILP Materials as Effective Catalysts in Selective Monofunctionalization of 1,1,3,3-Tetramethyldisiloxane

Functionalized siloxanes are one of the most important classes of organosilicon compounds, thus the enhancement of current methods of its synthesis is an important issue. Herein, we present the selective and highly effective reaction between 1,1,3,3-tetramethyldisiloxane (TMDSO) and 1-octene (1-oct), using SILP (supported ionic liquid phase) materials containing a rhodium catalyst immobilized in three phosphonium ionic liquids (ILs) differing in the structure of cation. Studies have shown high potential for using SILP materials as catalysts due to their high catalytic activity and selectivity, easy separation process, and the possibility of reusing the catalyst in subsequent reaction cycles without adding a new portion of the catalyst. Using the most active SILP material SiO2/[P66614][NTf2]/[{Rh(μ-OSiMe3)(cod)}2] allows for reuse of the catalyst at least 50 times in an efficient and highly selective monofunctionalization of TMDSO.

Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by palladium(II) isatin Schiff base complex supported into three-dimensional mesoporous silica KIT-6

In this work, the catalytic activity of a palladium(II) isatin Schiff base complex immobilized into mesoporous silica KIT-6 (Pd-isatin Schiff base@KIT-6) was studied for the oxidation of different alcohols with tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as an oxidant under solvent-free conditions. To find the suitable reaction conditions, the effect of essential factors including the solvent, temperature, catalyst amount and kind of oxidant on the oxidation of benzyl alcohol was explored. The results showed that in this catalytic system, the corresponding aldehydes and ketones were obtained with high to excellent yields at 50 °C without the formation of carboxylic acids as by-products. The catalyst was easily recovered by simple filtration and reused in five subsequent reaction cycles without any significant loss in the catalytic activity. Moreover, the comparison of the Fourier transform infrared (FT-IR) spectrum, X-ray diffraction (XRD) pattern, scanning and transmission electron microscopy (SEM and TEM) images of the used catalyst with a fresh one showed that the structure of the Pd-isatin Schiff base@KIT-6 catalyst remained intact after five times of reuse.

Enhanced Performance of Zirconium-Doped Ceria Catalysts for the Methoxycarbonylation of Anilines.

The methoxycarbonylation of anilines stands as an attractive method for the phosgene-free production of carbamates. Despite the high yields obtained for ceria catalysts, the reduction of the amount of side products and the prevention of catalyst deactivation still represent major hurdles in this chemistry. One advantage of ceria is the possibility of tuning its reactivity by doping its lattice with other metals. In the present work, a series of doped ceria-based materials, prepared by substitution with metals, are evaluated in the methoxycarbonylation of 2,4-diaminotoluene with dimethyl carbonate. Among all catalysts, containing Eu, Hf, La, Pr, Sm, Tb, Y or Zr, ceria promoted with 2 mol % Zr exhibited 96 % selectivity towards the desired carbamates, improving the pure CeO2 catalyst. Density functional theory demonstrates that two descriptors are needed: 1) a geometric factor that governs the reduction of energy barriers for carbamate formation through ureas; 2) catalyst basicity as N-H bonds need to be activated. Assessment in subsequent reaction cycles revealed that the CeO2 -ZrO2 catalyst is more stable than bulk CeO2 , along with the reduction of fouling processes.

Enzyme-free signal amplified Au nanoparticle fluorescence detection of thrombin via target-triggered catalytic hairpin assembly

Herein, we proposed an enzyme-free target-triggered catalytic hairpin assembly (CHA) for signal amplified fluorescence thrombin detection. In the detection system, two hairpin oligonucleotides (HP1, HP2) were used. The HP1 containing complimentary units forms a closed stem structure which brings the fluorescein (FAM) near the gold nanoparticle (AuNP) surface where they will be quenched. Upon addition of thrombin, the CHA could be initiated to form HP1-HP2-thrombin complex, which then through strand displacement process, the complex transforms into double-strand HP1-HP2 with a rod-like structure with the release of thrombin and also sequestering fluorophore from quencher surface, resulting in fluorescence recovery. The released thrombin further participated in subsequent reaction cycles, hence, the signal of the detection system significantly amplified. The method showed a limit of detection (LOD) of 165 pM with a linear range from 0.2 to 100 nM. The proposed method could be used as a potential application in complex biological matrices.

Enantioselective Transesterification of Allyl Alcohols with (E)-4-Arylbut-3-en-2-ol Motif by Immobilized Lecitase™ Ultra

Lecitase™ Ultra was immobilized on four different supports and tested for the first time as the biocatalyst in the kinetic resolution of racemic allyl alcohols with the (E)-4-arylbut-3-en-2-ol system in the process of transesterification. The most effective biocatalyst turned out to be the enzyme immobilized on agarose activated with cyanogen bromide (LU-CNBr). The best results (E > 200, ees and eep = 95–99%) were obtained for (E)-4-phenylbut-3-en-2-ol and its analog with a 2,5-dimethylphenyl ring whereas the lowest ee of kinetic resolution products (90%) was achieved for the substrate with a 4-methoxyphenyl substituent. For all substrates, (R)-enantiomers were esterified faster than their (S)-antipodes. The results showed that LU-CNBr is a versatile biocatalyst, showing high activity and enantioselectivity in a wide range of organic solvents in the presence of commonly used acyl donors. High operational stability of LU-CNBr allows it to be reused in three subsequent reaction cycles without negative effects on the efficiency and enantioselectivity of transesterification. This biocatalyst can become attractive to the commercial lipases in the process of the kinetic resolution of allyl alcohols.

Synergistic effect of functional groups in carbonaceous spheres on the formation of fuel enhancers from glycerol

Carbonaceous microspheres with tunable surface chemistry were prepared via sustainable hydrothermal carbonization combined with subsequent thermal treatment and/or SO3H-functionalization (with sulfuric acid or 4-benzenediazonium sulfonate). Various techniques (including SEM and TEM, elemental and textural analysis, potentiometric titration, TGA method, and XPS measurement) were used for determination of physico-chemical properties of the obtained materials. The results revealed that the effectiveness of applied acidic modifications was related to the structural features of the samples. Catalytic properties of the sulfonated carbons were further tested in glycerol acetylation with acetic acid performed in a batch mode at 80 °C. The experiments showed that the carbonaceous spheres treated with sulfuric acid were very active in the reaction, giving high glycerol conversion and high combined selectivity to diacetin (DA) and triacetin (TA), important fuel enhancers, after a relatively short time. Especially good results were achieved using SO3H-functionalized spheres richly decorated with oxygen groups such as carboxylic and hydroxyl/phenol ones. Finally, reusability measurements demonstrated good catalyst stability in subsequent reaction cycles. Additional investigations of the re-used system confirmed only small leaching of active sites from the tested material.

Continuous Flow Bioamination of Ketones in Organic Solvents at Controlled Water Activity using Immobilized ω-Transaminases.

Compared with biocatalysis in aqueous media, the use of enzymes in neat organic solvents enables increased solubility of hydrophobic substrates and can lead to more favorable thermodynamic equilibria, avoidance of possible hydrolytic side reactions and easier product recovery. ω‐Transaminases from Arthrobacter sp. (AsR−ωTA) and Chromobacterium violaceum (Cv−ωTA) were immobilized on controlled porosity glass metal‐ion affinity beads (EziG) and applied in neat organic solvents for the amination of 1‐phenoxypropan‐2‐one with 2‐propylamine. The reaction system was investigated in terms of type of carrier material, organic solvents and reaction temperature. Optimal conditions were found with more hydrophobic carrier materials and toluene as reaction solvent. The system's water activity (aw) was controlled via salt hydrate pairs during both the biocatalyst immobilization step and the progress of the reaction in different non‐polar solvents. Notably, the two immobilized ωTAs displayed different optimal values of aw, namely 0.7 for EziG3−AsR−ωTA and 0.2 for EziG3−Cv−ωTA. In general, high catalytic activity was observed in various organic solvents even when a high substrate concentration (450–550 mM) and only one equivalent of 2‐propylamine were applied. Under batch conditions, a chemical turnover (TTN) above 13000 was obtained over four subsequent reaction cycles with the same batch of EziG‐immobilized ωTA. Finally, the applicability of the immobilized biocatalyst in neat organic solvents was further demonstrated in a continuous flow packed‐bed reactor. The flow reactor showed excellent performance without observable loss of enzymatic catalytic activity over several days of operation. In general, ca. 70% conversion was obtained in 72 hours using a 1.82 mL flow reactor and toluene as flow solvent, thus affording a space‐time yield of 1.99 g L−1 h−1. Conversion reached above 90% when the reaction was run up to 120 hours.

Preparation of Na2O supported CNTs nanocatalyst for efficient biodiesel production from waste-oil

The present work demonstrated the preparation of sodium oxide impregnated on carbon nanotubes (CNTs) and its application as a heterogeneous catalyst for transesterification of waste cooking oil. The catalyst was prepared by impregnation of metal oxide such as sodium oxide, Na2O on the CNTs by calcination at 500 °C for 3 h. It was assumed that the positive metal ion which is Na+ (cations) possess Lewis acidity, whereby, high negativity of oxygen ions can acts as the Brønsted bases, which could enhance the activity of the catalyst. The characterization of synthesized Na2O impregnated-CNTs nanocatalyst was performed using Temperature-programmed desorption of carbon dioxide (TPD-CO2), X-ray diffraction (XRD), infrared spectroscopy and Field emission scanning electron microscope (FESEM). Herein, the mechanism of the transesterification process assisted by the Lewis acidic metal oxide on carbon support was proposed and explained. Series of reactions were carried out to determine the performance of the catalyst. It was found that the prepared Na2O(20 wt%)/CNTs catalysts yielded above 97% of FAME yield at 65 °C assisted by 3 wt% of catalyst amount and 20:1 of methanol-to-oil molar ratio in 3 h of reaction time. Moreover, the results on catalyst’s reusability indicated that the catalyst could last for 3 subsequent reaction cycles due to deactivation of the catalyst caused by leaching of metal oxides and poisioning effect on the active sites. It can be concluded that the prepared Lewis acidic carbon catalyst has a potential to catalyse the production of biodiesel from waste cooking oil (WCO).

Sulfonated activated carbon from corn cobs as heterogeneous catalysts for biodiesel production using microwave-assisted transesterification

Biodiesel is produced by transesterification reaction of oils catalyzed by homogeneous catalysts, with the latter being non-recoverable and promoter of solubility of the produced glycerol into the otherwise immiscible ester phase, which have to be purified. The need for purification of products is eliminated if heterogeneous catalysts are employed, with the added advantage of the catalyst recovery, however, with disadvantage of requiring drastic reaction conditions (elevated temperatures and pressures, longer reaction times) significantly increasing the costs of production. To overcome such problems, several catalysts were developed, with the sulfonated ones being the most prospective for industrial applications. Thus, the objective herein was to develop a sulfonated heterogeneous catalyst using activated carbon produced from corncobs as precursor material and employ it in microwave-assisted transesterification reactions of soybean oil with ethanol. The optimum operational conditions employed for the reaction were microwave variable power of 0–600 W, catalyst-to-oil mass ratio of 20%, alcohol-to-oil molar ratio of 6:1 and reaction time of 20 min. The catalyst successfully catalyzed the transesterification reaction in times as short as 20 min, resulting in a pure biodiesel phase with yield of 88.7%. The catalyst was reused in five subsequent reaction cycles without loss of its catalytic activity.

Enhanced Synthesis of Fatty‐Acid Methyl Ester using Oil from Palm Oil Mill Effluents and Immobilized Palm Lipase

AbstractOil from palm oil mill effluents (POME) was utilized as the substrate for fatty‐acid methyl ester (FAME) production using lipase from palm fruit immobilized to chitosan beads as a catalyst. The optimal reaction conditions consisted of a methanol‐to‐oil ratio of 6:1 mol mol−1, 6 g immobilized lipase per 10 g of POME oil at an incubation temperature of 35°C, a mixing speed of 200 rpm (with a 5 cm orbital diameter), and a reaction time of 24 h. Under optimal conditions, the FAME content was 93.6% methanol‐free basis. In addition, immobilized lipase retained 90.5% after six subsequent reaction cycles (compared with the FAME content of the first batch). The properties of FAME were characterized and found to fulfill both Thailand and ASTM standards.

Polymer-Supported Zn-Containing Imidazolium Salt Ionic Liquids as Sustainable Catalysts for the Cycloaddition of CO2: A Kinetic Study and Response Surface Methodology

Metal-containing ionic liquids (MIL) are highly active homogeneous catalysts for the chemical fixation of CO2 into epoxides yielding five-membered cyclic carbonates. To obtain sustainability, polymer-supported MIL catalysts were designed to overcome their previously reported inherent poor recoverability. Polymer-supported Zn-containing imidazolium salts, PS-(Im)2ZnX2, possessing bifunctional properties were identified as sustainable catalysts for the activation of CO2 under solvent-free conditions. PS-(Im)2ZnX2 showed good catalytic performance and was readily recoverable and reusable in the subsequent reaction cycles for the cycloaddition of CO2 to propylene oxide. Kinetic studies for the cycloaddition of CO2 to propylene carbonate using batch or semibatch systems were performed to calculate the approximate rate constants, which provide an explanation for the different reaction systems. In addition, process optimization using the response surface methodology was performed, and the interactions between th...

New insights on the basicity of ZnAl–Zr hydrotalcites activated at low temperature and their application in transesterification of soybean oil

Abstract