Hydrogen In Carbon Nanotubes Research Articles

Non‐covalent Immobilization of Chiral Rhodium Catalysts on Carbon Nanotubes for Asymmetric Hydrogenation

Non‐covalent Immobilization of Chiral Rhodium Catalysts on Carbon Nanotubes for Asymmetric Hydrogenation

Dual-core drive hydrogen transfer heterogeneous catalysts based on iridium-enzyme co-modified carbon nanotubes for aromatic aldehyde hydrogenation

Here, a novel dual-core drive transfer hydrogen heterogeneous catalysts Ir@CNT@ADH were developed by sequentially immobilizing the NADH-dependent alcohol dehydrogenase ADH and high active NADH-regenerated catalyst Pyren-Ir1 on the surface of carbon nanotubes. Two pyrene-functionalized Ir-complex, Pyrene-Ir1 and Pyrene-Ir2, were synthesized and demonstrated exceptional coenzyme NADH generation performances, ensuring continuous in situ NADH generation in the enzyme-catalyzed process. These complexes could be easily modified onto carbon nanotube materials by mild π-π conjugated adsorption. The catalysts Ir@CNT@ADH showed significantly improved catalytic hydrogenation efficiency in the reduction of benzaldehyde to the corresponding alcohol, compared to the single Pyrene-Ir1 modified carbon nanotube catalyst Ir@CNT and homogeneous catalytic system in the presence of a catalytic amount of NAD+. The yield of benzyl alcohol increased by more than 50 % in all cases. We assume that the designed dual-core drive heterogeneous catalyst strategy could effectively address the mutual inactivation problem of enzyme and Iridium complexes by blocking the contact between enzymes with Iridium complexes and enhancing the in situ regeneration property of coenzyme NADH in the enzyme catalytic system. Furthermore, catalyst Ir@CNT@ADH also demonstrated excellent catalytic hydrogeneration performances for various substituted benzaldehyde with good recycling performance. Therefore, the proposed dual-core drive heterogeneous catalyst strategy holds great potential for the combined industrial application of chemical catalysts and bioenzymes. It is expected to contribute to the development and preparation of higher-value biochemical products.

Tunable auxeticity in hydrogenated carbon nanotube origami metamaterial

Tunable auxeticity in hydrogenated carbon nanotube origami metamaterial

Ni Single Atoms Confined in Nitrogen-Doped Carbon Nanotubes for Active and Selective Hydrogenation of CO2 to CO

Developing efficient non-precious-metal catalysts capable of selectively converting CO2 into fuels and chemicals is desirable yet remains a challenge. Ni-based catalysts usually exhibit high activity in methanation reactions but low selectivity and stability in the reverse water-gas shift (RWGS) reaction. Herein, we report a Ni single-atom catalyst with Ni–Nx motifs confined in N-doped carbon nanotubes as an active, selective, and stable catalyst for the RWGS reaction, achieving almost 100% CO selectivity with a STY of 1.88 molCO gNi–1 h–1 at 500 °C and atmospheric pressure. In addition to weak CO adsorption, strong CO2 adsorption and weak H2 adsorption at the Ni–Nx active site were found to be responsible for the high catalytic activity and CO selectivity.

Ni Nanoparticles supported on N-doped carbon nanotubes for efficient hydrogenation of C5 hydrocarbon resins under mild conditions

The catalytic hydrogenation of hydrocarbon resins to high value-added products represents a prospective technology to upgrade the pyrolysis gasoline byproduct, while pore diffusion is challenging. Herein, Ni nanoparticles supported on nitrogen-doped carbon nanotubes (Ni/NCNTs) were designed and synthesized via an impregnation method. The as-prepared Ni/NCNTs exhibit superior hydrogenation of large molecular C5 hydrocarbon resins (C5HR) catalytic activity under mild conditions relative to that reported by literature, and the degree of hydrogenation (DH) for C5HR with a water-white appearance reach up to 95.5%. Combined with the BET, TEM, XPS, H2-TPR analysis results, the catalytic performance of Ni/NCNTs catalyst could ascribe to that the unique structure of NCNTs carrier provides a more accessible surface area that accounts for 88.1% of the specific surface area to expose abundant active sites, and small nickel nanoparticle sizes (less than 10 nm). Additionally, Ni/NCNTs exhibit higher stability for C5HR hydrogenation than Ni/CNTs catalyst, which attributes to the efficient anchor ability of N defect and the formation of Ni–N units.

Chitosan derived N-doped carbon nanotubes for selective hydrogenation of nitroarenes to anilines

Selective hydrogenation of nitroarene to aniline is a key reaction for the manufacture of fine chemicals, pharmaceuticals, and dyes. In this study, N-doped carbon nanotubes (NCNTs) are prepared by the pyrolysis of chitosan-CNTs composite. The outside diameter of CNTs, concentration of chitosan, pyrolysis temperature and heating rate are tuned to improve the catalytic performance. The catalyst of CS/CNTs-800 doped with 0.33% pyrrolic N and 0.30% graphitic N exhibits good activity and high selectivity for the hydrogenation of nitroarenes. The kinetics data reveal that the hydrogenation reaction is zero-order for 4-nitrophenol and first-order dependence to H2 pressure, and H2 dissociation on the active sites is the rate-determining step. On CS/CNTs-800, the nitro groups of 12 different substrates can be selectively reduced with the protection of the other reducible groups. Nonpolar H radicals are found to be formed on CS/CNTs-800 for efficient hydrogenation. In addition, the catalyst showed good stability.

The Adhesion and Diffusion of Saturate, Asphaltene, Resin and Aromatic (SARA) Molecules on Oxygenated and Hydrogenated Carbon Nanotubes (CNTs)

The interfacial adhesion between asphalt binder and carbon nanotubes (CNTs) depends on many nanoscopic properties such as diffusion of SARA molecules on CNTs surface. Functionalization of CNTs with Oxygens (O=CNTs), hydroxyl groups (HO–CNTs), and hydrogens (H–CNTs) has been an effective way to modify the surface properties of CNTs and ultimately the macroscopic properties of the CNT-composites. This paper presents the effect of different dosages of oxygenated and hydrogenated CNTs on the adhesion and diffusion of SARA molecules on CNTs’ surfaces. First, reactive molecular dynamics simulation is used to oxygenate and hydrogenate CNTs up to a certain dosage. Next, it is employed to model the interaction and diffusion of SARA molecules with the functionalized CNTs. We employ the steer molecular dynamic (SMD) and Einstein formula to calculate the adhesion and diffusion properties. The results demonstrate that hydrogenation has little effect on the adhesion energy, while oxygenation can increase adhesion energy up to 100% for 25% dosage. The diffusion coefficient dramatically drops for both oxygenated and hydrogenated CNTs, with lower values for the latter. We observe that for hydrogenated and oxygenated CNTs at different dosages, asphaltene, resin, aromatic, and saturate molecules have the highest to lowest values, respectively.

Structure and stability of deformed partially hydrogenated carbon nanotubes

In this paper, we study the effect of the axial deformation of carbon nanotubes in the zigzag and armchair directions on the stability of the interface between hydrogenated and non-hydrogenated regions. We analyze the specific energy of this interface as a function of the axial strain. We found that the clear interface can be obtained at a wider temperature range due to tube stretching. The energy barriers characterizing the process of hydrogen migration from the hydrogenated region of the nanotube to the pristine tube are calculated. It is concluded that the tube deformation significantly affects the stability of the system. For some tubes applied strain can qualitatively change the regularity of hydrogenation, changing the sign of the interface energy.

Cobalt Nanoparticles Apically Encapsulated by Nitrogen‐doped Carbon Nanotubes for Oxidative Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

AbstractIt is important to develop a highly active and stable transition‐metal catalyst with dual‐functional properties in the reversible transformations between various saturated and unsaturated N‐heterocycles. Herein, we prepared the cobalt nanoparticles (Co NPs) apically encapsulated by the N‐doped carbon nanotubes catalyst (Co@NCNTs) via a multiple pyrolysis of low‐cost dicyandiamide and cobalt (II) acetylacetonate. The catalyst shows excellent activity and recyclability towards the oxidative dehydrogenation (ODH) and the catalytic transfer hydrogenation (CTH) for various N‐heterocycles. The structure of outer N‐doped carbon nanotubes (NCNTs) can protect Co NPs from aggregation and leaching. Moreover, the encapsulated Co NPs and the NCNTs may generate a synergistic effect. Both of them facilitate the high performance. The poisoning tests with KSCN were to clarify the different active sites for ODH and CTH reactions: the Co NPs could modify the NCNTs through electrons redistribution, therefore the NCNTs could directly activate O2 in ODH. The encapsulated Co NPs is enhanced by the doped N atoms which is good for the H2 activation in CTH. What's more, the mechanisms of ODH and CTH reactions were also proposed. This work provides a facile and low‐cost method to design catalysts, which are dual‐functional, highly active and stable, for industrial applications.

New aspects in the study of carbon-hydrogen interaction in hydrogenated carbon nanotubes for energy storage applications

The paper presents the results of the combined investigation of changes in the carbon nanotubes structure caused by hydrogenation. Hydrogen adsorption by bundles of single-wall carbon nanotubes (SWNTs) was simulated by the molecular mechanics and DFT-LDA methods and applied to interpret the results of the experimental study carried out by using high-resolution X-ray absorption and photoelectron spectroscopy. As a result, new aspects of physical and chemical adsorption of hydrogen atoms on SWNTs were revealed, as well as preferable ways for SWNTs hydrogenation. Due to van-der-Waals interactions, location of hydrogen molecules inside the channels is energetically more favorable than that outside the channels. Chemical covalent bonds between hydrogen atoms and nanotube walls arise with formation of the C4H and C2H phases. However, not the entire surface of the SWNTs located inside the bundles is accessible for hydrogenation but only segments adjacent to triangular pores.

Ab initio study of the exo-hydrogenated single wall carbon nanotubes

Stability of the fully exo-hydrogenated zigzag (n,0) and armchair (n,n) single wall carbon nanotubes (CnHn) is studied using first-principles calculations. Zigzag and armchair carbon nanotubes (CNTs) were found to be different in electronic and atomic structures with respect to chemical hydrogenation. It was noted that the binding energy of hydrogenated carbon nanotubes revealed an approximately inverse proportionality behaviour with their diameter. Moreover, each single hydrogen atom was attached to nanotube by an exothermic process. The similar diameter exo-hydrogenated zigzag nanotubes were found to be energetically more favourable than armchair nanotubes. The calculated values of band gaps in small hydrogenated zigzag CNTs were found to be higher in both types of hydrogenated CNTs. These findings were important for particular functionalization of hydrogenated carbon nanotubes and improve the understanding to separate similar diameter zigzag and armchair nanotubes from each other through chemical functionalization.

Superconductivity in hydrogenated carbon nanostructures

We present an application of density functional theory for superconductors to superconductivity in hydrogenated carbon nanotubes and fullerane (hydrogenated fullerene). We show that these systems are chemically similar to graphane (hydrogenated graphene) and like graphane, upon hole doping, develop a strong electron phonon coupling. This could lead to superconducting states with critical temperatures approaching 100 K, however this possibility depends crucially on if and how metallization is achieved.

Mechanical properties of diamond nanothread reinforced polymer composites

One-dimensional diamond nanothread (DNT) has drawn intensive research interests and become a promising candidate for nanocomposites reinforcement. This paper explores the mechanical properties of DNT reinforced poly (methyl methacrylate) (PMMA) composite under tensile deformation via molecular dynamics simulation. The study shows that the Young's modulus and yielding stress of PMMA composite are enhanced by 85% and 15% with the incorporation of DNT. Remarkably, DNT which is a hydrogenated carbon nanotube (CNT) is proved to strengthen PMMA composite more effectively than CNT for a similar structure. The outstanding strengthening of DNT is attributed to interfacial interaction and mechanical interlocking between DNT and PMMA matrix. A pull-out simulation is conducted to examine the interfacial shear strength of DNT-PMMA interface and comparison studies are made with that of CNT-PMMA interface. The results reveal that DNT has higher load transference within PMMA composite than CNT, by presenting 34% above CNT in interfacial shear strength. It is also demonstrated that DNT morphology can significantly affect the interfacial interaction and mechanical interlocking with PMMA matrix, leading to distinguished reinforcement efficiency for PMMA composite. These findings will shed light to DNT application in nanocomposites and provide an important insight into reinforcing mechanism.

Thermodynamics and vibrational study of hydrogenated carbon nanotubes: A DFT study

Thermodynamic stability of the hydrogenated carbon nanotubes has been explored in the chemisorption limit. Statistical physics and density functional theory calculations have been used to predict hydrogen release temperatures at standard pressure in zigzag and armchair carbon nanotubes. It is found that hydrogen release temperatures decrease with increase in diameters of hydrogenated zigzag carbon nanotubes (CNTs) but opposite trend is noted in armchair CNTs at standard pressure of 1 bar. The smaller diameter hydrogenated zigzag CNTs have large values of hydrogen release temperature due to the stability of CH bonds. The vibrational density of states for hydrogenated carbon nanotubes have been calculated to confirm the CH stretching mode caused by sp3 hybridization.

Trace iron impurities deactivate palladium supported on nitrogen-doped carbon nanotubes for nitrobenzene hydrogenation

Nitrogen-doped carbons can effectively stabilize noble metal particles to achieve high catalytic performances. However, the metallic impurities in carbon nanomaterials, e.g. the residual growth catalysts of carbon nanotubes (CNTs), have some unforeseen effects on the catalysis involving nanocarbons. Herein, we demonstrate that the residual growth catalysts of N-doped CNTs (NCNTs) may significantly deactivate Pd catalysts for the hydrogenation of nitrobenzene. Through high-resolution transmission electron microscopy and CO-stripping, it was determined that the N dopants improved the dispersion of Pd nanoparticles. However, the iron, at ppm level, in residual catalysts encapsulated inside NCNTs can transfer onto the surface of Pd to block active sites so that the activity of Pd/NCNTs was much lower than that of Pd/CNTs. The similar effect was observed for most of the common metallic impurities in carbon materials, including Co, Ni, Mn, Cr, Cu, Zn, Mo, Al and Mg. To exploit the N-doped carbons, we deposited N-doped carbon layers on purified CNTs through pyridine pyrolysis and then supported Pd nanoparticles. By this means, the activity of Pd for nitrobenzene hydrogenation was improved by 3.85 folds compared to conventional CNTs, emphasizing the importance of controlling impurities in N-doped carbon materials for high performance catalysts.

Thermal stability of hydrogenated small-diameter carbon nanotubes

The initial stage of hydrogen desorption from fully hydrogenated carbon nanotubes (3.0) and (2.2) is numerically studied by the molecular dynamics method. The temperature dependence of the desorption rate is directly determined at T = 1800–2500 K. The characteristic desorption times are determined at temperatures outside this range by extrapolation. It is shown that hydrogen desorption leads to the appearance of electronic states in the band gap.

Nanosized Pd-Au bimetallic phases on carbon nanotubes for selective phenylacetylene hydrogenation.

Palladium (Pd)-catalyzed selective hydrogenation of alkynes has been one of the most studied hydrogenation reactions in the last century. However, kinetic studies conducted to reveal the catalyst's active centers have been hindered because of dynamic surface changes on Pd during the reaction. In the present study, bimetallic Pd-Au nanoparticles supported on carbon nanotubes have been synthesized at room temperature as catalysts for selective hydrogenation of phenylacetylene, which show effectively enhanced selectivity compared to their monometallic counterparts. Structural and surface analyses of fresh and reacted catalysts reveal that selective hydrogenation of phenylacetylene is favored over nanosized Pd-Au bimetallic phases due to modifications in the Pd surface in terms of neighboring site isolation and electron density reduction.

Hydrogenated carbon nanotube-based spin caloritronics.

Spin caloritronics has drawn much attention as it combines thermoelectrics and spintronics together. Carbon-based structures, such as graphene, have been found to exhibit different kinds of spin caloritronic features. However, a study of spin caloritronics in carbon nanotubes (CNTs) is still lacking. Using first-principles calculations, we investigate the spin-Seebeck effect (SSE) in partially hydrogenated CNTs. It is found that linear hydrogenation could make CNTs acquire magnetism and exhibit the spin-Seebeck effect. Moreover, an odd-even effect of the SSE is observed, where the even cases could be used as spin-Seebeck diodes. Further analysis shows that, it is induced by the difference of band structures, where the band structure of a tube is a combination of that of graphene-nanoribbon parts "divided" by hydrogenation. This mechanism could be extended to nanotubes with different diameters, showing great application potential. We believe that our results are very useful for the development of nanotube-based spin caloritronic devices.

Disintegrative activation of Pd nanoparticles on carbon nanotubes for catalytic phenol hydrogenation

Inactive annealed Pd NPs can be disintegratively re-dispersed and re-activated through a HNO3 vapour treatment for enhanced catalytic phenol hydrogenation.

Highly oxidized Pt species stabilized inside carbon nanotubes for asymmetric hydrogenation

The chemical state and its influence on Pt species in or outside of the channels of CNTs and the effect on the asymmetric hydrogenation of α-ketoester were investigated. XPS analysis showed that 13% Pt species in a highly oxidized state (Pt4+) were stabilized inside the channels in the presence of Na+. There were more highly oxidized Pt species inside the CNTs than outside. The highly oxidized Pt species promoted the interaction between the nanoparticle and chiral modifier, which is crucial for high enantioselectivity. Hydrogen temperature programmed desorption showed that Pt nanoparticles confined in the channels can better activate hydrogen, which contributed to their high activity even at low hydrogen pressure.