Search

Heterogeneous catalysis is an important branch of sustainable chemistry. In this work, a series of polyacrylonitrile fiber (PANF) fiber catalysts (PANF-E, PANF-EDs, and PANF-D) with different catalytic micro-environments are developed and characterized by elemental analysis, Fourier-transfer infrared spectroscopy, x-ray diffraction, thermogravimetric/differential scanning calorimetry analysis, scanning electron microscopy, and mechanical strength measurements to demonstrate the successful immobilization of the different amines as well as evaluate the physical strength and thermal stability of the fiber catalysts at different stages. The catalytic activities of the fiber catalysts are tested by one-pot three-component Knoevenagel-Michael reaction to the synthesis of substituted 2-amino-4H-chromenes in which the influences of surface polarities, kinds and proportions of functional groups on the fiber catalysts activities were investigated. Among the prepared catalysts, the PANF-D with higher density of tertiary amino group and hydrophilic micro-environment exhibited the best catalytic activity to efficiently catalyze the three-component reaction in water with excellent substrate suitability (92-98%). In addition, the catalyst can be easily separated from the catalytic system and conveniently reused at least ten times. Moreover, the PANF-D performs well in scaled-up experiment in a simple fixed-bed reactor with a yield of 97% which allows it to have great potential for further cleaner industrial applications. [ABSTRACT FROM AUTHOR]

Abstract: The l-lysine functionalized polyacrylonitrile fiber (PANLF) was prepared by grafting the l-lysine into a commercially available polyacrylonitrile fiber and showed highly catalytic activity for Knoevenagel condensation reaction. With low temperature (45 °C) and short reaction time (1 h), the fiber catalyst was well applicable to Knoevenagel condensation of a wide range of aldehydes and the yields could reach up to 99%. Interestingly, only in water could the reaction take place smoothly (with a yield of 88%) and a polar micro-environment promoted reaction process had been proposed to explain this phenomenon. Besides, the fiber catalyst has advantages of easy preparation, high functional degree, strong mechanical strength and thermal stability, etc. And it can be reused at least 5 times without further treatment and performed well in scaled-up experiment (amplified 50 times) and flow chemistry experiment (no loss of catalytic activity after 48 h), which indicates its potential application in industry application.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Polyacrylonitrile fibers were functionalized with different amines to construct special tridimensional catalytic microenvironments at the surface. The polarity of the microenvironments at the surface of the fiber catalyst was tuned by changing the ratio of hydrophobic and hydrophilic amines. The catalytic performances of these microenvironments were examined for a cyanation reaction in water. Among these fiber catalysts with different microenvironments, the one modified with more hydrophobic benzylamine groups (PANBTF) shows much higher catalytic activity than that modified by hydrophilic ethanolamine groups. PANBTF can efficiently and rapidly catalyze the cyanation reaction of benzaldehyde and ethyl cyanoformate in water with a yield of 94 % at room temperature within 40 min. Moreover, a mechanism promoted by the hydrophobic microenvironment has been proposed to explain the high and specific catalytic activity of PANBTF. In addition, this fiber catalyst exhibited excellent recyclability and reusability (8 times) without further treatment, and it also performed well in flow-chemistry tests and scaled-up experiments, which indicated potential for the application of PANBTF in industrial production. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation method of fiber catalyst is simple. • The reaction was carried out under mild conditions. • The chosen fiber catalyst PAN T-UdA F-I is highly efficient and recyclable. • Possible mechanism based on the fiber's microenvironment is proposed. Fiber-supported quaternary ammonium catalysts for the fixation of CO 2 with epoxides were designed and prepared via amination and quaternization of polyacrylonitrile fiber, followed by ion exchange with different anions. The impact of different quaternary ammonium structures and counter anions on the reaction yields was investigated. A fiber catalyst (PAN T-UdA F-I) with a C 11 carboxylic acid chain and iodide counter anion exhibited excellent catalytic activity in the fixation of CO 2 with epoxides under mild and solvent-free conditions (80 °C, 0.1 MPa) with a very low catalyst amount (0.5 mol%), and diverse cyclic carbonates were obtained in yields between 24–99 %. PAN T-UdA F-I could be conveniently separated by filtration and showed good recyclability and durability till the 4th cycle. Novel cooperative catalytic mechanism is proposed where the ionic microenvironment plays a crucial role to stabilize the ionic intermediates and lowers the activation energy of the reaction. [ABSTRACT FROM AUTHOR]

• Facile synthesis and detailed characterization. • High catalytic activity and substrate selectivity. • Prominent recyclability and superior stability. • Extremely simple separation procedure and efficient scaled-up process on a simple fixed-bed reactor. Acid-base bifunctional catalysis represents a significant approach for achieving enzyme-like catalytic activity. In this study, we present a concise and direct approach for constructing acid-base bifunctional aramid fiber catalysts, enabling one-pot tandem deacetalization-Knoevenagel reactions in an aqueous environment. The fiber catalysts were conveniently prepared from commercially available aramid fiber using a straightforward two-step procedure, and comprehensively characterized using various detection techniques. Additionally, the acid-base cooperativity of the AF catalyst was effectively controlled through the manipulation of the acid-base ratios within the catalysts. Notably, the AF-SN1/2 catalyst exhibited superior catalytic activity in the one-pot tandem deprotection-Knoevenagel reaction at room temperature, resulting in the production of high yields. Moreover, the AF-SN1/2 catalyst demonstrated exceptional recyclability and performed admirably in a scaled-up experiment utilizing a straightforward fixed-bed reactor. These findings suggest that the AF-SN1/2 catalyst holds significant promise for future applications in cleaner industrial processes. [Display omitted] [ABSTRACT FROM AUTHOR]

• Oriented design, facile synthesis and detailed characterization of the novel bifunctionalized fiber catalyst. • Highly selectively catalytic activity for CO 2 cycloaddition with epichlorohydrin under mild conditions. • Simple separation procedure and excellent recyclability of the fiber catalyst-mediated system. Converting CO 2 into useful chemical materials has uniquely high value in both chemical and resource-oriented sense. In this work, several kinds of bifunctional polyacrylonitrile fiber catalysts were developed and applied to selectively catalyze the fixing of CO 2 with epichlorohydrin. Compared to the synergistic effect, the surface polar effect is the major influence factor for the catalytic activity of the fiber catalyst, which is different from other support catalysts and has been explained detailly in this work. Among the synthesized fiber catalysts, benzylamine and N , N' -dimethyl- N -(4-pyridyl)-1,3-propanediamine (DA) bifunctionalized fiber (PAN BD F) has excellent high catalytic activity for its lower polar microenvironment. Different PAN BD Fs with various benzylamine and DA modified degrees were prepared to inspect the influences of benzylamine and DA amounts on the catalytic activity. PAN BD F (benzylamine and DA modified degrees are 0.93 mmol/g and 0.16 mmol/g, respectively) can complete the reaction of epichlorohydrin and CO 2 (97% conversion) under 0.1 mol% catalyst dosage at 80 °C with a CO 2 balloon. Under very low catalyst amount (0.0125 mol%), it can also effectively catalyze the reaction with 56% conversion and the TOF reaches up to 9333.3 h−1. Furthermore, the fiber catalyst can be reused at least five times which indicates a potential to value-added chemistry. [ABSTRACT FROM AUTHOR]

Abstract Two fiber supported tertiary amine catalysts were prepared by immobilization of 3-dimethylamino-1-propylamine (PAN D F) and 3-dimethylamino- N -methylpropylamine (PAN T F) on polyacrylonitrile fiber. Both fiber catalysts contain polar microenvironments constructed by amide groups, tertiary amine groups and unreacted cyano groups. The difference between the two catalysts lies in that the PAN D F contains hydrogen bond network while the PAN T F does not. Employing Knoevenagel condensation as a model reaction, the cooperative action of immobilized tertiary amines with hydrogen bonds was evaluated in detail. At the same time, the aggregation of reactants in the polar microenvironment under different solvents was also investigated. The results showed that hydrogen bonds and the supporting basic groups can promote the reaction by the synergistic catalytic effect in most solvents. The catalysts displayed different catalytic behaviors in solvents with different polarities. The catalysts can achieve highly efficient catalytic activity in the more polar solvents which were well compatible with the catalysts. Moreover, the reaction can also occur in less polar solvents due to their incompatible property with the fiber catalysts, which can compel the polar reactants to accumulate on the fiber surface with strong polar microenvironment. Highlights • Two types of microenvironment were constructed on the surface of polyacrylonitrile fiber. • Hydrogen bond has a synergistic catalytic effect with the immobilized basic group in most solvents. • The polar microenvironment on the surface of fiber catalyst can gather reactant in less polar solvents. [ABSTRACT FROM AUTHOR]

• Prepare a novel quinine functionalized fiber (PAN QN F) used to asymmetric reaction. • The PAN QN F possess high catalytic activity, enantioselectivity and recyclability. • Asymmetric Michael addition is catalyzed excellently by PAN QN F with ee up to greater than 99%. • (S)-2-amino-4H-pyran derivatives are prepared by PAN QN F with ee greater than 99%. As a new type of catalyst support, polyacrylonitrile fiber (PANF) has diverse advantages in physical and chemical properties. Quinine and its derivatives have been widely used as asymmetric organocatalysts recently. By combining the advantages of PANF and quinine, a novel fiber-based asymmetric catalyst (PAN QN F) was successfully prepared through thiol-ene click reaction and characterized by FTIR, XRD, EA, SEM, TGA and mechanical strength analysis. The PAN QN F exhibited excellent catalytic performance for asymmetric Michael addition of malononitrile to chalcone with ee up to > 99%. Further research revealed that the (S)-2-amino-4 H -pyran derivatives were also successfully prepared using PAN QN F as a catalyst in asymmetric tandem Michael addition-nucleophilic annulation of α -phenylchalcone and malononitrile, and the ee of the tandem reaction can also reach greater than 99%. In addition, as an immobilized catalyst, PAN QN F showed relatively wide temperature tolerance and good recycling performance. Overall, the fiber catalyst has the advantages of easy preparation, high activity, high enantioselectivity, wide reaction temperature range, simple separation and good recyclability, which exhibits great potential for industrial application. [ABSTRACT FROM AUTHOR]

In this work, photocatalytic cement was prepared by loading Bi 2 WO 6 microspheres with Portland cement. 3D hierarchical Bi 2 WO 6 microspheres were synthesized by self-assembly of 2D nanosheets and nanoplates firstly. Interestingly, Backscattered Electron (BSE) images showed Bi 2 WO 6 hierarchical structure remained unchanged on the surface of hydration cement. The nanoplate and nanosheets which fell off from the Bi 2 WO 6 microspheres distributed evenly on the surface of the hydration products. As to the inner structure of Bi 2 WO 6 /cement, a porous structure was observed and Bi 2 WO 6 particles were located evenly in the pores. This result was in favor of enhancing photocatalytic performance and gas adsorption. The 15 wt% Bi 2 WO 6 /cement showed the highest photocatalytic activity, which can degrade the HCHO completely within 80 min under visible light. XRD and hydration heat results showed that Bi 2 WO 6 hardly influences the hydration process. However, when the Bi 2 WO 6 dosage was increased to beyond 15%, the hydration process was deterred and hydration heat decreased, which may influence the durability of the cement matrix. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel Pd(0) nanoparticle-functionalized polyacrylonitrile fibers have been prepared. • The chosen fiber catalyst PAN GQA F-Pd(0) is highly efficient and recyclable. • Possible mechanism based on the fiber's microenvironment is proposed. Palladium salts and Pd(0) nanoparticles were immobilized on a series of amine and quaternary ammonium functionalized polyacrylonitrile fibers (PANFs) to prepare functionalized fiber catalysts. The catalytic activities of these materials for Heck reaction were investigated. Among which, the Gemini quaternary ammonium fiber immobilized Pd(0) nanoparticles catalyst PAN GQA F-Pd(0) exhibited the best catalytic activity, which was able to effectively catalyze Heck reaction and 4-nitrophenol (4-NP) reduction with high yields of 76–99%. And the catalyst can tolerate an extensive scope of substrates under mild reaction conditions. In addition, PAN GQA F-Pd(0) was easily recovered, and it can be reused 10 times with little decrease in catalytic activity and low Pd leaching (only 3.69%). The experimental results confirmed that Pd(II) was converted into Pd(0) during the coupling reactions, which helped to promote the reaction. This explains why the catalytic activity of PANF-immobilized Pd(0) is better than that of PANF-immobilized Pd(II). Accordingly, possible mechanisms for the catalytic Heck reaction and reduction reaction of PAN GQA F-Pd(0) were proposed. [ABSTRACT FROM AUTHOR]

A series of polyacrylonitrile fibers (PANF) functionalized with nitrogen-containing ligands were prepared and then used to synthesize fiber-supported Pd(0) nanoparticle catalysts. The phenanthroline-functionalized PANF with immobilized Pd(0) nanoparticles (PAN Phen F-Pd(0)) had the best catalytic activity for the Heck reaction under solvent-free conditions. The PAN Phen F-Pd(0) efficiently stabilized the nanoparticles and they were well-dispersed with Pd(0) particle sizes of about 3 nm. The PAN Phen F-Pd(0) structure was further characterized by a variety of instrumental methods. A probable mechanism based on the fiber's microenvironment is proposed for the Heck reaction catalyzed by PAN Phen F-Pd(0). The PAN Phen F-Pd(0) catalyst is easily recovered from the reaction system and can be used up to six times with only a slight decrease in catalytic activity and with low Pd leaching. The PAN Phen F-Pd(0) catalyst also has excellent catalytic activity for gram-scale use. [Display omitted] • Novel Pd(0) nanoparticle-functionalized polyacrylonitrile fibers serve as catalysts to catalyze Heck reaction. • The chosen fiber catalyst PAN Phen F-Pd(0) is highly efficient, selective and recyclable. • Possible mechanism based on the fiber's microenvironment is proposed. [ABSTRACT FROM AUTHOR]