Fiber Catalyst Research Articles

Quaternary ammonium functionalized polyacrylonitrile fiber supported phosphotungstic acid as efficient heterogeneous catalyst: Hydrophobic tuning of the catalytic microenvironment

Thirteen novel amine or quaternary ammonium functionalized polyacrylonitrile fiber (PANF) supported phosphotungstic acid (PTA) catalysts were designed and prepared, and their catalytic activities were screened by choosing condensation/annulation tandem synthesis of 2,3-dihydroquinazolin-4(1H)-one compound via C–N bond formation between 2-aminobenzamide and p-chlorobenzaldehyde as a model reaction. By adjusting the functionality and hydrophobic/hydrophilic property of the amine/ammonium structure as well as the density of PTA sites, the fiber catalyst CAT-12 prepared from quaternary ammonium functionalized PANF containing benzyl group with high PTA loading achieved the best catalytic activity for most reactions in water. The CAT-12 can be easily separated from the reaction system and recycled for 7 times without significant loss of catalytic activity. Moreover, the reaction proceeded smoothly in gram scale and gave nearly quantitative yield using this efficient, eco-friendly and easily recyclable catalyst with great industrial potential which was also demonstrated in Friedel-Crafts alkylation of indoles with β-nitrostyrene. Vivid PTA immobilization processes and the corresponding “catch-catalyze” catalytic modes were further schematically described to address the effect of microenvironment-tuning on immobilization and catalysis, and accordingly the possible catalytic mechanisms of the two reactions were proposed.

Superficial properties of activated carbon fiber catalysts produced by green synthesis and their application in water purification.

Catalysts of Pd-In supported on activated carbon fiber were synthesized, characterized, and evaluated for the removal of nitrogen oxyanions from water. The work was carried out aiming the development of a green synthesis process, and the studies were accomplished with the following objectives: (a) to evaluate whether catalysts produced by wet impregnation (WI) and autocatalytic deposition (AD) have enough catalytic activity for the removal of oxyanions in water; (b) to determine the efficiency of ion removal using formic acid as a reducing agent; (c) to determine which synthesis method produces less waste. It was found that the two synthesis processes modified the properties of the support and that the distribution of the particles of the metallic phase was of the nanometric order, being these particles found predominantly at the support surface. By using formic acid as a reducing agent, although low nitrate conversions were obtained (32%), a selectivity to N2 higher than 99% was achieved. These findings were attributed to the low decomposition of formic acid on the catalyst surface. The Pd:In (0.45:0.2) catalyst prepared by WI was the most suitable for the catalytic reduction of both nitrate and nitrite oxyanions. Regarding the green point of view of the synthesis method, catalysts prepared by WI generated less waste. Graphical abstract.

The key role of photoisomerisation for the highly selective photocatalytic hydrogenation of azobenzene to hydrazobenzene over NaNbO3 fibre photocatalyst

NaNbO3 fibre catalyst can efficiently hydrogenate azobenzene to hydrazobenzene with 100 % selectivity under Xe light irradiation. The catalytic activity was closely dependent on the trans-cis photoisomerisation of azobenzene and the subsequent moderate activation of cis NN bond on Nb site. The adsorption of azobenzene with cis or trans conformation on the Nb active site was investigated by the computational methods. The apparent increase of the cis NN bond length from 1.254 to 1.348 Å, suggested an effective activation. The important role of the cis isomer in the reaction was also reflected in the quenching experiment, in which a silver quencher was used to inhibit the generation of the cis isomer. The weak interaction between Nb site and NN of hydrazobenzene was the key to inhibit the over reduction, which was confirmed by the in situ diffuse-reflectance IR spectra.

Surface characterization of metal oxides-supported activated carbon fiber catalysts for simultaneous catalytic hydrolysis of carbonyl sulfide and carbon disulfide

The sol–gel method was used to synthesize a series of metal oxides-supported activated carbon fiber (ACF) and the simultaneous catalytic hydrolysis activity of carbonyl sulfide (COS) and carbon disulfide (CS2) at relatively low temperatures of 60°C was tested. The effects of preparation conditions on the catalyst properties were investigated, including the kinds and amount of metal oxides and calcination temperatures. The activity tests indicated that catalysts with 5 wt.% Ni after calcining at 400°C (Ni(5)/ACF(400)) had the best performance for the simultaneous catalytic hydrolysis of COS and CS2. The surface and structure properties of prepared ACF were characterized by scanning electron microscope-energy disperse spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), carbon dioxide-temperature programmed desorption (CO2-TPD) and diffuse reflectance Fourier transform infrared reflection (DRFTIR). And the metal cation defects were researched by electron paramagnetic resonance (EPR) method. The characterization results showed that the supporting of Ni on the ACF made the ACF catalyst show alkaline and increased the specific surface area and the number of micropores, then improved catalytic hydrolysis activity. The DRFTIR results revealed that -OH species could facilitate the hydrolysis of COS and CS2; -COO and -C–O species could facilitate the oxidation of catalytic hydrolysate H2S. And the EPR results showed that high calcination temperature conditions provide more active reaction center for the COS and CS2 adsorption.

Rational design of ceramic hollow fibre catalyst, a new option for efficient removal of organic pollutants

Metallic catalysts have presented high activity for the degradation of pollutants. However, the inevitable metal leaching would lead to secondary pollution, which hinders the development of metallic catalysts for water treatment. Membrane technology would be an effective way to conquer this, especially hollow fibre membrane with numerous micro-pores and high surface area per unit volume. The good recoverability and stable repeatability proved that the ceramic hollow fibre membrane would be a promising form of metallic catalysts for aqueous phase reaction.

Ionic liquid polyoxometalate-enhanced Pd/N,P-codoped coal-based carbon fiber catalysts for formic acid electrooxidation

Direct formic acid fuel cells have great application potential in the energy field, but their commercialization is hindered by the CO poisoning and low performance of Pd-based anode catalysts. In this study, novel composite catalysts composed of Pd, organic-inorganic hybrid imidazole ionic liquid polyoxometalates, and N,P-codoped coal-based carbon fibers with good dispersion and smaller Pd nanoparticles were synthesized successfully. Physical and electrochemical characterizations revealed that the as-prepared Pd-based composite catalysts have excellent CO poisoning resistance and enhanced electrocatalytic activity in formic acid electrooxidation. Notably, the CO oxidation onset potential of a catalyst modified by imidazole ionic liquid polyoxometalate with long alkyl chain was 0.1 V lower than that of the unmodified catalyst. The mass activity of the as-prepared Pd catalyst in formic acid oxidation was 754.1 mA mg−1Pd. It is expected that organic-inorganic hybrid polyoxometalates can be further applied to fuel cell catalysts.

Preparation and characterization of Cu and Mn modified beta zeolite membrane catalysts for toluene combustion

Cu and Mn as well as their mixed oxides modified beta zeolite membrane (Beta) coating on paper-like stainless steel fibers (PSSF) catalysts were successfully prepared and applied in toluene combustion. Firstly, Beta/PSSF with different crystallization temperature, crystallization time, Si/Al ratios etc. were prepared using secondary growth method, meanwhile, XRD, SEM and N2 adsorption-desorption isotherms were utilized to analyze the structures of the samples, respectively. Then, Cu and Mn as well as their mixed oxides loaded onto the obtained beta zeolite membrane with the optimal parameter were prepared by impregnating method. Finally, toluene combustion experiment was performed over a fixed-bed reactor. The experimental results depicted that continuous and well-intergrown beta zeolite membrane covered on the PSSF with typical truncated bipyramidal shape, and Beta/PSSF had a three-dimensional network with large void volume and majority of microporous. For the catalysts, the copper element existed as Cu2+ and Cu1+, and manganese element existed as Mn4+, Mn3+, and Mn2+. As a result, the catalytic activities for toluene combustion over mixed oxides as catalysts were superior to the single metal oxide catalysts. The T10, T50 and T90 of toluene combustion were dramatically decreased over Cu-Mn (1:3)- Beta/PSSF.

Synergistic catalysis of bifunctional polyacrylonitrile fiber for the synthesis of (E)-α,β-unsaturated esters from aldehydes by decarboxylative Doebner–Knoevenagel reaction

A series of monofunctional and bifunctional polyacrylonitrile fiber catalysts have been successfully prepared to catalyze the decarboxylative Doebner–Knoevenagel reaction of aldehydes and monoethyl malonate for the syntheses of the (E)-α,β-unsaturated esters. Among which, the catalyst PANPDFII/I shows the best synergistic catalytic activity with high yields (89–96%), stereoselectivities (Z:E>99:1) and reusability (up to 8 times). The influences of the N position on aminopyridine moiety, solvent and temperature on the catalytic system were investigated in detail. This catalytic system can process well in higher or lower polar organic solvents instead of moderate polar solvents, which is an interesting phenomenon in organic catalysis, and the reasons are explained in this work. Furthermore, a DMAP (4-dimethylaminopyridine) and piperazine synergistic catalytic mechanism in the micro-environment of the fiber catalyst has been conceived to explain the high catalytic performance of this catalytic system. Besides, the fiber catalyst PANPDFII/I shows high application potential in industry for its good performance in scaled-up experiment, as well as its advantages of the easy preparation, high mechanical strength, flexibility and high stability in air.

Selective hydrogenation of acetylene over Pd on glass fiber catalysts

Key properties of silicate glasses are highlighted including the capability of stabilizing disperse Pd nanoparticles in the bulk of glass fibers (GF), high solubility of acetylene and hydrogen, as well as their high mobility. These properties provide the high activity and selectivity of Pd/GF catalysts to hydrogenation of acetylene in excess ethylene over a wide range of acetylene conversions up to its complete one. For a wide variety of mono-, bimetallic systems including catalysts with single palladium atoms, TOF was established to depend only slightly on the palladium dispersion and support nature, i.e. the reaction can be considered structure-insensitive. Nevertheless, a TOF decrease was observed in the systems with single atoms; that was accounted for by declining of the hydrogen dissociation rate or its slower spillover. Isotope-kinetic data were used for determining quantitatively undesirable contributions to the process selectivity caused by both hydrogenation of acetylene and gas-phase ethylene to ethane. High selectivities of alloyed bimetallic systems comprising isolated palladium atoms at approaching to the complete conversion of acetylene were caused by the low rate of hydrogenation of weakly adsorbed ethylene to ethane while for Pd/GF catalysts by the complete exclusion of the hydrogenation of ethylene from gas-phase.

Preparation of a Pt/Active Carbon Fiber Catalyst and Its Application in the Synthesis of p-Chloroaniline with Catalytic Hydrogenation.

In this study, a Pt loaded active carbon fiber (Pt/ACF) catalyst was prepared by immobilizing Pt nanoparticles on ACF. The catalyst accelerated hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CA) at lower temperature and atmospheric pressure, resulting in approximately 100% yield and selectivity. Several factors that affect p-CA yield were investigated. The nitro reduction rate reached 100% under the optimal reaction conditions, indicating excellent selectivity of the prepared catalyst. This process will overcome the environmental pollution problems associated with the traditional process, and is a green synthetic process.

Bifunctionalized polyacrylonitrile fibers as highly efficient and selective heterogeneous catalysts for cycloaddition of CO2 with epichlorohydrin under mild conditions

Abstract Converting CO2 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 CO2 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 (PANBDF) has excellent high catalytic activity for its lower polar microenvironment. Different PANBDFs with various benzylamine and DA modified degrees were prepared to inspect the influences of benzylamine and DA amounts on the catalytic activity. PANBDF (benzylamine and DA modified degrees are 0.93 mmol/g and 0.16 mmol/g, respectively) can complete the reaction of epichlorohydrin and CO2 (97% conversion) under 0.1 mol% catalyst dosage at 80 °C with a CO2 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.

Positional influence of Ru on Perovskite structured catalysts for efficient H2 production process by heavy-hydrocarbon source

Direct conversion of heavy-hydrocarbon source into H2–rich gas fuels has been highlighted as an efficient ultraclean system. Dictating the productivity of the system, the most important factor lies with the activity and physical/chemical stability of the catalytic materials. In this work, perovskite hollow fiber catalysts by partial substitution of Cr with Ru in the B site for LaCrO3 (LaCr1-xRuxO3, x = 0–0.4) are designed to investigate the effects of the positional and chemical changes of Ru on the catalytic properties at autothermal reforming of heavy-hydrocarbon. From a novel synthesis method, a hollow fibrous perovskite nanoparticle network is prepared to provide high surface area. Depending on the Ru doping levels, the optimal Ru amount exists as lattice type Ru, while an excess Ru resulted in the formation of surface type Ru on the perovskite. Especially, a slight structural modification of the orthorhombic structure owing from the doped Ru results in the increase of the surface oxygen and reducibility due to the high-valanced Cr and Ru states. After autothermal reforming of heavy-hydrocarbon including sulfur, it is obvious that the mixed lattice and surface Ru type shows a large deactivation due to the strong binding energy with carbon and sulfur. In contrast, less coke formation and sulfur poisoning are revealed for the catalyst with mostly lattice type Ru through the stable Ru species and high amount of active oxygen. Consequently, the hollow perovskite fiber catalyst of LaCr0.8Ru0.2O3 displays the optimal activity to extract the highest amount of H2 from the heavy-hydrocarbon source with exceptional stability.

Proton sponge functionalized polyacrylonitrile fibers as an efficient and recyclable superbasic catalyst for Knoevenagel condensation in Water

Fiber catalysts with high catalytic activity and good recyclability have attracted much attention. In this work, proton sponge 1,8-bis(dimethylamino)naphthalene functionalized polyacrylonitrile fiber is prepared to construct a superbasic microenvironment, which is applied to catalyze the Knoevenagel condensation in water for the synthesis of α,β-unsaturated compounds. Different characterization techniques of XPS, 13C solid-state NMR, FTIR, SEM etc. Are used to verify the successful grafting of the proton sponge during modification as well as evaluate the stability of the fiber catalyst in specific application. The fiber catalyst exhibits distinctly higher catalytic activity and efficiency in water than in other solvents, with a low catalytic dosage of 5 mol% under room temperature within 3 h. Besides, a synergistic microenvironment can be formed between the hydrophilic polar surface of the fiber and the superbasic catalytic sites, promoting the efficient catalysis of Knoevenagel condensation reaction. In addition, the fiber possesses high reusability that it can be easily recovered and reused for at least 10 times without obvious loss of its catalytic activity. More interestingly, the fiber can be fixed in a reactor to catalyze the Knoevenagel condensation, in which process pure α,β-unsaturated compounds are continuously obtained by simple filtration, avoiding the use of toxic solvents and time-consuming column chromatography, which presents great potential in cleaner and more efficient production. In brief, with such advantages as high catalytic activity, simple separation operation and good economic efficiency, the proton sponge modified fiber is fairly attractive in fixed-bed reactors in cleaner industrial production.

Polyacrylonitrile fiber with strongly acidic electrostatic microenvironment: Highly efficient and recyclable heterogeneous catalyst for the synthesis of heterocyclic compounds

Four categories of sulfonic acid functionalized fiber catalysts with different surface microenvironments were synthesized by covalent grafting using polyacrylonitrile fiber (PANF) as the support. After the effect of acid structure on catalytic activity has been investigated by Friedlander reaction, PANEOSF was chosen for the synthesis of quinolines and coumarin derivatives with high yields and extensive substrate scope (51 examples) in ethanol or water. The effect of electrostatic microenvironment and solvent has been discussed, and a “release-catch-release-catch” catalytic pattern was proposed accordingly. PANEOSF can be easily recycled for 20 times without any decrease of catalytic activity.

Prolinamide functionalized polyacrylonitrile fiber with tunable linker length and surface microenvironment as efficient catalyst for Knoevenagel condensation and related multicomponent tandem reactions

A series of new prolinamide polyacrylonitrile fiber catalysts with tunable length of alkyl linker and different linker group were prepared by covalent bonding for the first time and well characterized by mechanical strength, FT-IR, XRD, EA, TGA, SEM and water contact angel. The catalytic activities of these fiber catalysts were evaluated in Knoevenagel condensation and one-pot Knoevenagel-Michael multicomponent tandem reactions to synthesize α, β-unsaturated nitrile and 2-amino-4H-chromene derivatives in water. The result show that the suitable linker length attaching amines to fiber matrix as well as the constructed hydrophobic microenvironment by linker group within the surface layers of fiber materials effectively promotes the reactions. In addition, the good swollen capacity of fiber in solvent ensure that the reaction proceed well. Fiber catalyst PANPA−2F modified by prolinamide with a C2 alkyl chain exhibited the best catalytic performance and can be easily recovered and reused for at least ten consecutive cycles without significant loss of catalytic activity and active sites leaching.

Synthesis of TiO2 on different substrates by chemical vapor deposition for photocatalytic reduction of Cr(VI) in water

AbstractTiO2 loaded on several substrates such as carbon fiber, aluminum plate, silica plate, and glass plate was prepared using the chemical vapor deposition (CVD) method for the photocatalytic reduction of Cr(VI) in water with the presence of ethanol under Ultraviolet (UV) illumination. As‐prepared samples were characterized by X‐Ray Diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM). The catalyst with TiO2 loaded on carbon fiber possessed an extremely large surface area (1,463,91 m2/g), while the other catalysts possessed small surface areas (0.05–0.21 m2/g). The photocatalytic activity of TiO2 loaded on carbon fiber, which was determined by the conversion of Cr(VI) and the degradation of chemical oxygen demand (COD), was much higher than that of other catalysts. The reusability of TiO2 loaded on carbon fiber catalyst exhibited almost the same activity as the fresh catalyst. The results indicated that TiO2 loaded on carbon fiber is feasible for practical application.

Tuning anion species and chain length of ligands grafted on the fiber for an efficient polymer-supported Ni(II) complex catalyst in one-pot multicomponent A3-coupling

Herein, a new series of polymer-supported Ni(II) complex catalysts with different ligand chain lengths grafted on the fiber for one-pot multicomponent A3-coupling reactions, is reported. The fiber catalysts were prepared conveniently from commercially available polyacrylonitrile fiber via a simple two-step procedure by polyamine-amination and nickel-chelation in water respectively, and the resulting materials from the modification and utilization processes were characterized detailedly by morphology, mechanical property, elemental analysis, FTIR spectroscopy and SEM. Moreover, the fiber-supported Ni(II) complex catalysts with chlorine anion and longer chain ligands exerted higher efficiency than short chains, and the mediated reactions showed broad applicability and proceeded smoothly to afford a number of substituted propargylamines under mild conditions. Furthermore, the newly developed fiber catalyst held high strength, good flexibility and exhibited excellent stability and recyclability (over 15 cycles), and the procedure was scalable on a gram scale in a concise spinning basket reactor with good industrialization prospect.

Electrospun vanadium oxide based submicron diameter fiber catalysts. Part II: Effect of chemical formulation and dopants

The first part of present paper described the synthesis procedure for the preparation of VOx/ZrO2 catalysts with fibrous morphology. In the present contribution, the same procedure is applied for the preparation of multimetallic catalysts, such as V-Mo-O/ZrO2 and V-Nb-O/ZrO2. In all the cases, and in only one step, the multimetallic porous fibers were obtained. The characterization data has shown that the segregation of metal atoms is adequate, avoiding the formation of oxides such as V2O5, Nb2O5 and/or Mo2O3, and the activity under the propane ODH reaction of VOx based catalysts is improved by the addition of Mo.

Electrospun vanadium oxide based submicron diameter fiber catalysts. Part I: Preparation procedure and propane ODH application

V-Zr-O submicron diameter fibers have been prepared by electrospinning of V and Zr containing solutions in only one calcination step. This is a simple and versatile synthesis method, easy to scale up, that produces porous solids, with fibrous morphology and with VOx catalytically active species, being these solids attractive for alkane partial oxidation reactions, since the catalysts with fibrous morphology present several advantages with respect powered ones. With the new proposed method, at low vanadium loadings (V% w/w<6.4), surface dispersed VOx were found in the zirconia fiber as shown by Raman spectroscopy analysis, whereas crystalline ZrV2O7 was observed when the V content was increased (V% w/w>6.4). These fibers were very active for the propane oxidative dehydrogenation (ODH) catalytic reaction, showing very promising results since the fibrous morphology of submicrometric diameter makes these solids quite suitable for fixed-bed catalytic reactors.

Aminosilane-Grafted SiO2–ZrO2 Polymer Hollow Fibers as Bifunctional Microfluidic Reactor for Tandem Reaction of Glucose and Fructose to 5-Hydroxymethylfurfural

In this study, we demonstrate the concept of tandem reaction for glucose and fructose to 5-hydroxymethylfurfural (HMF) in an aminosilane-grafted SiO2–ZrO2 polyamide–imide hollow fiber that acts as a bifunctional heterogeneous catalyst and microfluidic reactor. The bifunctional catalysts were formed by embedding SiO2 and ZrO2 nanoparticles into polyamide–imide polymer dope that underwent subsequent phase inversion through “dry-jet, wet-quench spinning” process to form hollow fibers, followed by postgrafting with aminosilane to incorporate amine moieties into the hollow fibers. The tandem strategy integrated the first step of glucose isomerization with the subsequent step of dehydration of fructose to HMF over bifunctional Lewis and Bronsted acid sites of hollow fiber microfluidic reactor at different temperatures (100–150 °C) and reaction times (1–8 h). Our results indicated, through optimizing the Lewis to Bronsted acid sites ratio in hollow fiber catalysts, the HMF selectivity was enhanced from 21% to 8...