Nanotube Catalyst Research Articles

Ni -chitosan/carbon nanotube: An efficient biopolymer -inorganic catalyst for selective hydrogenation of acetylene

This work developed an efficient Ni catalyst based on chitosan for selective hydrogenation of acetylene. The Ni catalyst was prepared by the reaction of the chitosan/carbon nanotube composite with NiSO4 solution. The synthesized Ni-chitosan/carbon nanotube catalyst was characterized by inductively coupled plasma, FTIR, SEM and XRD. The results of FTIR and XRD demonstrated that Ni2+ successfully coordinated with chitosan. The addition of chitosan greatly improved the catalytic performances of Ni-chitosan/carbon nanotube catalyst. Over the Ni-chitosan/carbon nanotube catalyst, both the acetylene conversion and the selectivity to ethylene all achieved 100% at 160 °C and 190 °C, respectively. The catalytic performances of 6 mg Ni-chitosan/carbon nanotube catalyst were even better than that of 400 mg Ni single atom catalyst in literature. Extending the crosslinking time of chitosan and increasing the amount of the crosslinking agent were beneficial to enhance the catalytic effect of Ni-chitosan/carbon nanotube catalyst.

Facile synthesis of nickel-based supported halloysite nanotube catalysts and their role in photocatalytic degradation of liquid epoxidized natural rubber

Facile synthesis of nickel-based supported halloysite nanotube catalysts and their role in photocatalytic degradation of liquid epoxidized natural rubber

Engineering 3D structure Mn/YTiOx nanotube catalyst with an efficient H2O and SO2 tolerance for low-temperature selective catalytic reduction of NO with NH3.

TiO2 with a 3D structure is considered to be a promising support for Mn-based catalysts for the NH3-SCR reaction, but it is still insufficient to solve problems such as poor N2 selectivity and tolerance of H2O/SO2 at low temperature. In this work, a novel 3D-structured Mn/YTiOx nanotube catalyst was designed and the role of Y on the catalytic performance was investigated for the NH3-SCR reaction at low temperature. The results indicated that the Y-doped TiOx gradually transformed from nanotubes to nanosheets with the increase in Y doping, leading to a reduction in specific surface area and Brønsted acid sites. An appropriate amount of Y doping could distinctly improve the dispersion of MnOx and increase the concentration of surface Mn4+, Lewis acid sites and chemisorbed oxygen of catalysts, which was beneficial to the low-temperature NH3-SCR reaction, while excessive Y doping could cause a sharp decrease in specific surface area and Lewis acid sites. Therefore, Mn/YTiOx catalysts exhibited a volcano-type tendency in NO conversion with an increase in Y doping, and the highest activity was obtained at 3% doping, showing more than 90% NO conversion and N2 selectivity in a wide temperature window from 120 to 320 °C. The N2 selectivity and H2O/SO2 resistance of the catalysts was also enhanced with the increase in Y doping mainly due to the increased chemisorbed oxygen and electron transfer between Y and Mn. An in situ DRIFTS study demonstrated that Lewis acid sites played a more important role in the reaction than Brønsted acid sites, and the coordinated NH3 absorbed on Lewis acid sites, -NH2, monodentate nitrate and free nitrate ions were the main reactive intermediate species in the NH3-SCR reaction over an Mn/3%YTiOx catalyst. Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) reaction mechanisms co-existed in the NH3-SCR reaction, but the L-H reaction mechanism predominated.

Rational design of metal–nitrogen-codoped carbon nanotube catalysts for CO2 reduction based on NiZn-layered double hydroxides

CNT-N-NiZn was constructed by controlling the assembly, high-temperature nitriding between single-layer NiZn-LDH and CNT. This study elucidates the M-N-C catalyst activity source and provides new insights into the M-N-C structure design.

Evaluation of the Effect of Catalysts on Ozone Mass Transfer and Pollutant Abatement during Laboratory Catalytic Ozonation Experiments: Implications for Practical Water and Wastewater Treatment

Adding catalysts can usually substantially enhance pollutant removal during laboratory semi-batch ozonation experiments with continuous ozone gas bubbling. However, it is unclear whether the enhanced pollutant abatement is mainly caused by the higher •OH yields (moles of •OH formed per mole of O3 consumed) or the higher O3 utilization efficiency in the presence of the catalysts─two effects that can or cannot be effectively transferred to large-scale applications, respectively. To distinguish these two effects during the laboratory experiments, this study compared oxalate removal by conventional ozonation (in the absence of catalysts) and catalytic ozonation with three carbon nanotube catalysts based on the consumed O3 doses during the different processes. In addition, the results of several previous studies that had evaluated varying catalysts (e.g., NiCo2O4, MnFe2O4, and MnO2) for pollutant removal by catalytic ozonation were revisited based on the consumed O3 doses measured in these studies. The results show that while all the catalysts considerably accelerated O3 transfer/consumption and pollutant removal during catalytic ozonation than during conventional ozonation, many of them did not enhance the extent of pollutant removal when the same O3 doses were consumed during the two processes. This finding suggests that in the laboratory experiments, these catalysts only enhanced the O3 utilization efficiency but did not significantly enhance the •OH yield from O3 decomposition during catalytic ozonation relative to conventional ozonation. Therefore, they may not be able to enhance pollutant removal during large-scale applications to the same extent as has been shown in the laboratory experiments. These results indicate that to more realistically predict the performance of catalysts for large-scale applications, the extent of pollutant removal should be evaluated based on the transferred/consumed O3 doses during the laboratory experiments.

Supramolecular preorganization synthesis of nitrogen-doped carbon nanotubes functionalized by Brønsted acidic ionic liquid for microwave-assisted production of promising furanic derivatives

Brønsted acidic ionic liquids functionalized nitrogen-doped carbon nanotubes catalysts, [C4SO3HN][OTf]-NCNTs (OTf = SO3CF3), are synthesized by an additive-free supramolecular preorganization-thermal condensation route followed by chemical modification. By controlling the molar composition of carbon–nitrogen based monomers, sequence of the monomers and thermal condensation temperature, the tubular morphology and porosity properties of the catalysts are well-adjusted. The [C4SO3HN][OTf]-NCNTs are successfully applied in the reactions of great relevance to the development of sustainable bio-economy, namely, microwave-assisted production of 5-hydromethylfurfural (HMF) and furfural (FFR) from the dehydration of fructose and xylose, and the important reaction parameters including microwave irradiation temperature and time as well as solvent are considered. Co-operation of strong Brønsted acidity, unique tubular nanostructures and microwave heating approach finally endows [C4SO3HN][OTf]-NCNTs the enhanced dehydration reactivity and selectivity, in which the [C4SO3HN][OTf]-NCNTs800-2 with perfect tubular nanostructures displays the highest HMF yield (82.6%, 15 min in THF media) and FFR yield (56.2%, 45 min in DMSO media). The [C4SO3HN][OTf]-NCNTs also exhibit good catalytic reusability, attributing to covalent bonding of the [C4SO3HN+][OTf−] units onto NCNTs frameworks; meanwhile, the formation of considerable amount of humins at the surface of the catalysts is effectively inhibited by using microwave heating mode.

Pd3Co1 Alloy Nanocluster on the MWCNT Catalyst for Efficient Formic Acid Electro-Oxidation

In this study, the Pd3Co1 alloy nanocluster from a multiwalled carbon nanotube (MWCTN) catalyst was fabricated in deep eutectic solvents (DESs) (referred to Pd3Co1/CNTs). The catalyst shows a better mass activity towards the formic acid oxidation reaction (FAOR) (2410.1 mA mgPd-1), a better anti-CO toxicity (0.36 V) than Pd/CNTs and commercial Pd/C. The improved performance of Pd3Co1/CNTs is attributed to appropriate Co doping, which changed the electronic state around the Pd atom, lowered the d-band of Pd, formed a new Pd-Co bond act at the active sites, affected the adsorption of the toxic intermediates and weakened the dissolution of Pd; moreover, with the assistance of DES, the obtained ultrafine Pd3Co1 nanoalloy exposes more active sites to enhance the dehydrogenation process of the FAOR. The study shows a new way to construct a high-performance Pd-alloy catalyst for the direct formic acid fuel cell.

Localized growth of atomic-layer-deposited platinum catalysts on plasma-treated surface of carbon nanotubes

Platinum–carbon nanotube (CNT) catalysts were evaluated for use as the cathode catalyst in polymer electrolyte membrane fuel cells. Pt catalysts were fabricated by atomic layer deposition (ALD) on bare untreated or O2 plasma treated CNTs. Pt formed as particles that uniformly covered both the bare and plasma-treated CNT supports. The Pt particles on the bare CNTs were relatively small, and the particle size increased with increasing number of ALD cycles. By contrast, Pt formed as sparsely deposited large particles on the plasma-treated CNTs. This morphological difference caused a clear difference in the electrochemical and fuel cell performance. Experiments confirmed that relatively high and stable power production can be obtained using the relatively large Pt catalysts grown on the plasma-treated CNTs. Factors other than electrochemical enhancement by the geometric features were also found to affect the fuel cell performance.

Single-atom Co-N5 catalytic sites on carbon nanotubes as peroxymonosulfate activator for sulfamerazine degradation via enhanced electron transfer pathway

Carbon-based single-atom cobalt catalysts exhibit high catalytic activity for the removal of novel pollutants in advanced oxidation processes. Here, atomically dispersed Co species with five-coordinated nitrogen atoms on carbon nanotubes (CNT) catalyst (Co-N5/CNT) was successfully fabricated via a low-temperature solvothermal reaction. The obtained Co-N5/CNT catalyst exhibited superior catalytic performance for PMS activation for sulfamerazine degradation. Its apparent rate constant kobs was 1.6 times higher than that of the Co-N4/CNT catalyst with four-coordinated nitrogen atoms prepared by the same method. Electron transfer non-radical mechanism was the main pathway for Co-N5/CNT to activate PMS. Higher single-atom cobalt metal loading (1.39 wt% vs 1.08 wt% in Co-N4/CNT) and significantly enhanced electron transfer ability (0.82 e vs 0.77 e in Co-N4/CNT) were the key factors for its superior catalytic performance. This work demonstrates a novel carbon-based single-atom cobalt catalyst for the removal of novel antibiotic contaminants by activating PMS in environmental catalysis applications.

Metal cobalt embedded N-doped carbon nanotube catalyst for catalytic ozonation

Through a one-step solid-state pyrolysis reaction, we construct a Co embedded N-doped carbon nanotube ([email protected]) catalyst for catalytic ozonation. The embedded Co and doped N effectively enhance the catalytic activity and stability of carbon nanotubes, and the core–shell structure effectively solves the problem of metal leaching. Experiment results showed that the [email protected] for catalytic ozonation could completely degrade 15 mg L-1 of methylene blue solution in 6 min, and the removal efficiency was about 35% higher than ozonation alone. Results of EPR experiments and quenching tests manifested that both.O2– and 1O2 were dominant ROS contributed to the improvement of degradation efficiency with [email protected]/O3 system.

Rational construction of FeNi3/N doped carbon nanotubes for high-performance and reversible oxygen catalysis reaction for rechargeable Zn-air battery

Metal-based alloys encapsulated in nitrogen-doped carbon (alloy@NC) catalysts with high-efficiency and cost-effective are promising to solve the sluggish kinetics of the oxygen reduction/oxygen evolution reaction (ORR/OER) in Zn-air batteries (ZABs). Here, a novel FeNi3 alloy nanoparticles encapsulated by N-doped carbon graphene nanotubes (FeNi3@NC) catalyst with 0D/1D/3D multi-structure is synthesized through combining ligand-assisted and in-situ catalytic assembly strategy. The hybrid catalyst FeNi3@NC exhibited highly efficient ORR catalytic activity and stability. Impressively, the FeNi3@NC only required an overpotential of 291 mV to drive a current density of 10 mA cm−2, successfully demonstrating their excellent bifunctional catalytic activity. Moreover, the assembled rechargeable Zn-air battery based on FeNi3@NC air electrode exhibited high power density of 149.7 mW cm−2 and specific capacity of 658 mAh gZn-1, and long-term stability up to 280 h, outperforming most of the recently reported catalysts. Density functional theory (DFT) reveals that C atom adjacent to the pyridinic-N in FeNi3@NC act as the active sites for ORR/OER, since the alloying FeNi3 combined by pyridinic-N effectively break electroneutrality of the C atom, thereby accelerating the kinetics process of the ORR/OER. This work provides some constructive guidelines for fabricating alloy@NC catalysts with bifunctional catalytic activity and deeply demonstrates the applicability modulate the electronic configuration to construct high-performance rechargeable ZABs.

Peroxymonosulfate activation by Mg-introduced Fe-N carbon nanotubes to accelerate sulfamethoxazole degradation: Singlet oxygen-dominated nonradical pathway

Here, Mg-introduced Fe-N carbon nanotube catalysts (FeMg@NCNTs) were prepared for peroxymonosulfate (PMS). Experiments suggested that the introduction of Mg improved the removal of sulfamethoxazole (SMX) and found a transformation from the original radical pathway to a nonradical pathway dominated by singlet oxygen (1O2). XPS characterization demonstrated an enhanced pyridinic N content with the introduction of Mg. SMX degradation was not inhibited by pH, coexisting ions, or humic acid (HA). The free radical scavengers and electron paramagnetic resonance (EPR) indicate that the primary reactive substance was 1O2. Experimentally, 1O2 was proven to have a predominant effect on the degradation of SMX. The concentration of 1O2 increased 6.37 times after the introduction of Mg. Four decomposition pathways and three fragile sites for SMX were proposed by DFT calculations and HPLC-MS. The toxicity estimation software tool (T.E.S.T) analyzed the intermediates with lower ecotoxicity than SMX. The different contaminants (CIP, BPA, TBBPA, TCS, TC and Rh B) had a removal rate of more than 99% at 60 min except TC. The removal rates of SMX in tap water, river water and lake water were 100%, 96.6% and 93.1% in 40 min, respectively. The SMX degradation efficiency remained good after 5 cycles of the experiment. FeMg@NCNTs hydrogel catalyst continuous flow device exceeded 90% within 15 h for SMX removal efficiency and the Rh B is always running at 99% removal rate. In conclusion, this work provides a singlet oxygen-dominated non-radical pathway activating material and provides a new option for antibiotic wastewater degradation and practical applications.

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

Effect of various metal-based halloysite nanotubes for the catalytic degradation of chitosan to low molecular weight chitosan

This article describes the application of metal-based supported halloysite nanotube (HNT-M2+, M2+ = Ni2+ or Cu2+) catalysts as an alternative route for the degradation of chitosan (CS) into low molecular weight chitosan (LMWC). Results from scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDX) analysis reveals the surface morphology of the HNT-M2+ catalysts with certain amount of agglomeration, which may suggest the incorporation of the metal species into the HNT support. X-ray photoelectron spectroscopy (XPS) further clarifies that Ni(OH)2 or Cu(OH)2 and CuO exist as active species in the catalysts. X-ray diffraction (XRD) spectra reveal the presence of a low intensity Cu(OH)2 peak in the HNT-Cu2+ catalyst. The absence of other Cu2+ species in the HNT-Cu2+ catalysts is due to the peak overlap with HNT. The diffractogram of HNT-Ni2+ also shows only HNT peaks. The pH at zero point charge (pHzpc) of the HNT-M2+ catalysts at 3.8, which is slightly lower than the reaction mixture pH (~3.9), enhances the degradation of CS due to electrostatic attraction between the catalyst surface and CS. The crystallinity index (CrI), viscosity, [η] and viscosity average molecular weight, Mv of LMWC were lower than those of CS due to the chain scission of the polymer backbone and loss of crystallinity, thus accounting for their high water solubility. The results revealed that the HNT-Cu2+ catalyst exhibited a better catalytic performance than HNT-Ni2+ for the degradation of CS. This is probably due to the different active species available on HNT-Cu2+.

Highly efficient and durable electrochemical hydrogen evolution reaction based on composition/shape controlled CuTi@Pt core-shell nanotubes in acidic media

High-quality electrocatalysts for hydrogen evolution reactions, which have long-term stability and high efficiency, are a major challenge. Enhancing electrocatalytic efficiency can be achieved by creating alloys, designing core–shell structures, and controlling shapes. Herein, we demonstrate an elevated performance CuTi@Pt alloy catalyst with a one-dimensional nanotube structure through a galvanic replacement reaction. While the Pt/Cu atomic ratio and the wall thickness of the nanotube are carefully tuned, the CuTi@Pt alloy phase and tube structure are consequentially controlled. A systematic investigation is then conducted into the differences in composition and shape that impact the activity and durability. The optimized CuTi@Pt nanotube catalyst shows significant enhancements in the HER activity (1.12-fold decrease in Tafel compared to the commercial Pt/C) and the durability (remains unchanged after 24 h).

High productivity of tartronate from electrocatalytic oxidation of high concentration glycerol through facilitating the intermediate conversion

Selective electro-oxidation of glycerol to value-added chemicals has attracted much attention both for the upgrading of biodiesel industry and the coupled electrolytic hydrogen production. Here we report Pt nanoparticles decorated, Fe- and N co-doped carbon nanotube (Pt/FeNC) catalyst for the selective electro-oxidation of glycerol to tartronate, one of the valuable chemicals used in pharmaceuticals. In a high concentrated glycerol solution of 5.0 M, the Pt/FeNC catalyst reaches the glycerol conversion of 94% and tartronate yield over 47% at 0.9 V vs. RHE, equivalent to a tartronate production rate of 1182 mmol/h/gPt, about 20 times of the highest value ever reported in a batch electrocatalytic reactor. The valence band analysis and kinetic experiments reveal that the FeNC mediates the adsorption behavior of the glycerate intermediate on Pt surface, and promotes the glycerate-to-tartronate oxidation. Moreover, the anchoring effect of FeNC ensures the stable catalytic performance for ten cycles.

Complete confinement of Ce/Ni within SiO2 nanotube with high oxygen vacancy concentration for CO2 methane reforming

CO2 reforming of methane (DRM) is currently one of the most promising processes to convert two green-house gases: CH4 and CO2 to value-added syngas, boosting CO2 utilization and promoting carbon neutralization. However, a major challenge of inexpensive and active Ni-based catalysts for DRM reactions is their easy sintering and carbon deposition issues. Herein, a series of bimetallic Ce/Ni nanoparticles completely confined within SiO2 nanotube (NT) catalysts were synthesized by the precipitation and coating method. Compared with Ni@SiO2, bimetallic xCe/Ni@SiO2 catalysts have higher specific activities for DRM reaction. In addition, 20Ce/Ni@SiO2 shows high and stable CH4 and CO2 conversions of 76.3% and 80.1%, respectively at 700 °C for 80 h. High Ni sintering resistance, high concentration of surface Ni and oxygen vacancies (Vo), high carbon resistance contribute to its outstanding DRM performance. The CO2 activation mechanisms via CeO2 and H* was revealed via in-situ DRIFTS study. The preparation method to completely confine bimetallic nanoparticles within SiO2 NTs sheds light on the design of other confined bi/tri-metallic catalysts with high sintering resistance to be applied in other high temperature reactions.

Ultrafast self-heating synthesis of robust heterogeneous nanocarbides for high current density hydrogen evolution reaction

Designing cost-effective and high-efficiency catalysts to electrolyze water is an effective way of producing hydrogen. Practical applications require highly active and stable hydrogen evolution reaction catalysts working at high current densities (≥1000 mA cm−2). However, it is challenging to simultaneously enhance the catalytic activity and interface stability of these catalysts. Herein, we report a rapid, energy-saving, and self-heating method to synthesize high-efficiency Mo2C/MoC/carbon nanotube hydrogen evolution reaction catalysts by ultrafast heating and cooling. The experiments and density functional theory calculations reveal that numerous Mo2C/MoC hetero-interfaces offer abundant active sites with a moderate hydrogen adsorption free energy ΔGH* (0.02 eV), and strong chemical bonding between the Mo2C/MoC catalysts and carbon nanotube heater/electrode significantly enhances the mechanical stability owing to instantaneous high temperature. As a result, the Mo2C/MoC/carbon nanotube catalyst achieves low overpotentials of 233 and 255 mV at 1000 and 1500 mA cm−2 in 1 M KOH, respectively, and the overpotential shows only a slight change after working at 1000 mA cm−2 for 14 days, suggesting the excellent activity and stability of the high-current-density hydrogen evolution reaction catalyst. The promising activity, excellent stability, and high productivity of our catalyst can fulfil the demands of hydrogen production in various applications.

Application of multi-wall carbon nanotubes supported l-proline in continuous flow catalysis

l-proline on multi-wall carbon nanotubes (l-proline/MWCNTs) catalysts doped with suitable auxiliary support materials are successfully applied in the continuous flow catalytic syntheses, including Aldol reaction, Mannich reaction and Knoevenagel condensation reaction. With the advantages of easy operation, high efficiency and excellent stability, this method is promising in large-scale synthesis.

Synthesis and Photocatalytic Activity of Pt-Deposited TiO2 Nanotubes (TNT) for Rhodamine B Degradation.

Dye wastewater has attracted more and more attention because of its high environmental risk. In this study, a novel TiO2 nanotube (TNT) catalyst was prepared and its morphology and structure were characterized. The synthetic catalyst was used to degrade Rhodamine B (RhB) under UV light and evaluated for the application performance. According to the characterization results and degradation properties, the optimum synthetic conditions were selected as 400°C calcination temperature and 10 wt% Pt deposition. As a result, the degradation efficacies were sequenced as TNT-400-Pt > TNT-500-Pt > TNT-400 > TNT-300-Pt. In addition, the effect of pH and initial concentration of RhB were explored, and their values were both increased with the decreased degradation efficacy. While the moderate volume of 11 mm of H2O2 addition owned better performance than that of 0, 6, and 15 mm. Scavengers such as tertbutanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na2), and nitroblue tetrazolium (NBT) were added during the catalytic process and it proved that superoxide radical anions , photogenerated hole (h+) and hydroxyl radical (OH•) were the main active species contributing for RhB removal. For the application, TNT-Pt could deal with almost 100% RhB, Orange G (OG), Methylene blue (MB), and Congo red (CR) within 70 min and still kept more than 50% RhB removal in the fifth recycling use. Therefore, TNT-Pt synthesized in this study is potential to be applied to the dye wastewater treatment.