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An increasing number of studies have demonstrated that confinement within carbon nanotubes (CNTs) provides an effective approach for the modulation of catalysis. It was generally predicted that confinement became stronger with a decreasing diameter of CNTs. However, our present study here overturns the previous expectation: the influence on catalysis is not monotonic. Instead, it exhibits a volcano relationship with CNT diameter. Taking Pt catalyzing O2 conversion and Re catalyzing N2 conversion as probes using density functional theory, we show that only within tubes with an i.d. of ∼1 nm can the activity of metal clusters be enhanced to its maximum. Furthermore, confinement only enhances the catalytic activity of metals with strong intrinsic binding with reactants, whereas it is suppressed for those with weak binding. These findings shed further light on the fundamental effects of confinement on catalysis, and could guide more rational design of confined catalysts.

We demonstrate that the methanation activity of Ni catalysts is modulated by the crystal phase of the TiO2 support. The rutile TiO2 (r-TiO2)-supported Ni catalyst gives a turnover frequency almost two orders of magnitude higher than the anatase TiO2 (a-TiO2)-supported catalyst although the two catalysts exhibit a similar mean Ni particle size. Characterization by H2-TPR, H2-TPD, XPS and IR reveals a stronger interaction between Ni and r-TiO2, leading to a higher capability of CO activation and hydrogenation activity of Ni although Ni is partially covered by TiOx overlayers during reaction. Interestingly, the modulating effects of the titania crystal phases are much more pronounced on the activity of Ni in CO2 methanation.

DAMPE satellite has directly measured the cosmic ray proton spectrum from 40 GeV to 100 TeV and revealed a new feature at about 13.6 TeV., The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 1/2 years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.

Despite significant efforts towards the direct conversion of syngas into liquid fuels, the selectivity remains a challenge, particularly with regard to high-quality gasoline with a high octane number and a low content of aromatic compounds. Herein, we show that zeolites with 1D ten-membered-ring (10-MR) channel structures such as SAPO-11 and ZSM-22 in combination with zinc- and manganese-based metal oxides (Zna Mnb Ox ) enable the selective synthesis of gasoline-range hydrocarbons C5 -C11 directly from syngas. The gasoline selectivity reached 76.7 % among hydrocarbons, with only 2.3 % CH4 at 20.3 % CO conversion. The ratio of isoparaffins to n-paraffins was as high as 15, and the research octane number was estimated to be 92. Furthermore, the content of aromatic compounds in the gasoline was as low as 16 %. The composition and structure of Zna Mnb Ox play an important role in determining the overall activity. This process constitutes a potential technology for the one-step synthesis of environmentally friendly gasoline with a high octane number from a variety of carbon resources via syngas.

The DArk Matter Particle Explorer (DAMPE), a satellite-based cosmic ray and gamma-ray detector, was launched on December 17, 2015, and began its on-orbit operation on December 24, 2015. In this work we document the on-orbit calibration procedures used by DAMPE and report the calibration results of the Plastic Scintillator strip Detector (PSD), the Silicon-Tungsten tracKer-converter (STK), the BGO imaging calorimeter (BGO), and the Neutron Detector (NUD). The results are obtained using Galactic cosmic rays, bright known GeV gamma-ray sources, and charge injection into the front-end electronics of each sub-detector. The determination of the boundary of the South Atlantic Anomaly (SAA), the measurement of the live time, and the alignments of the detectors are also introduced. The calibration results demonstrate the stability of the detectors in almost two years of the on-orbit operation.

In this work, we have studied the role of the 12-ring channel of mordenite in DME carbonylation. Upon modification with pyridine, the catalytic lifetime of mordenite in DME carbonylation was prolonged dramatically although its activity decreased slightly and the induction period increased. 1H MAS NMR and PFG-NMR results demonstrated that the acid quantity decreased after pyridine was adsorbed, and the self-diffusion coefficient of CH4 decreased with the increase in pyridine quantity in the 12-ring channel. 129Xe NMR results reveal that Xe atoms are preferentially adsorbed in an 8-ring side pocket at low pressure; xenon can enter the 8-ring side pocket at high temperature through the 12-ring channels only. From these results, the function of the 12-ring with respect to the reaction rate is explored and a transfer path of reactants/products is proposed.

Shale gas, which was recently discovered with a large reserve, has invoked wide interest as an alternative energy resource of natural gas. However, little is known about the molecular properties of shale gas (mainly methane) confined in the nanopores of shale, such as their diffusivity, which is essential for its exploitation and utilization. We study here the diffusivity of methane using 1H pulsed field gradient (PFG) NMR and theoretical modeling. Following analysis of the physicochemical properties of shale, a well-ordered mesoporous silica material (SBA-15) modified with organic functional groups is employed to model the mesopores observed in the shale and to study the fundamental behavior of shale gas. The results demonstrate that methane moves faster in the pores modified with the aromatic phenyl groups than those with nonaromatic cyclohexyl groups, suggesting a higher diffusivity of methane with increasing maturity of shale.

Small olefins from syngas The conversion of coal or natural gas to liquid fuels or chemicals often proceeds through the production of CO and H 2 . This mixture, known as syngas, is then converted to hydrocarbons with Fischer-Tropsch catalysts. For the light olefins (ethylene to butylenes) needed for chemical and polymer synthesis, conventional catalysts are mechanistically limited to et al. developed a bifunctional catalyst that achieves higher conversions and avoids deactivation (see the Perspective by de Jong). A zinc-chromium oxide creates ketene intermediates that are then coupled over a zeolite. Science , this issue p. 1065 , see also p. 1030

Syngas conversion by Fischer-Tropsch synthesis (FTS) is characterized by a wide distribution of hydrocarbon products ranging from one to a few carbon atoms. Reported here is that the product selectivity is effectively steered toward ethylene by employing the oxide-zeolite (OX-ZEO) catalyst concept with ZnCrOx -mordenite (MOR). The selectivity of ethylene alone reaches as high as 73 % among other hydrocarbons at a 26 % CO conversion. This selectivity is significantly higher than those obtained in any other direct syngas conversion or the multistep process methanol-to-olefin conversion. This highly selective pathway is realized over the catalytic sites within the 8-membered ring (8MR) side pockets of MOR via a ketene intermediate rather than methanol in the 8MR or 12MR channels. This study provides substantive evidence for a new type of syngas chemistry with ketene as the key reaction intermediate and enables extraordinary ethylene selectivity within the OX-ZEO catalyst framework.

Fe-based catalyst is an outstanding candidate for the Fischer-Tropsch reaction to get light olefins from syngas directly. However, exposed Fe species are susceptible to sintering and coking, which lead to deactivation. Here, we demonstrate that Fe nanoparticles encapsulated in pod-like carbon nanotubes (Pod–Fe) can be used as an efficient Fischer-Tropsch catalyst to produce light olefins. It gave a higher selectivity of light olefins (45%) and high stability over 120 h reaction (P = 0.5 MPa, T = 320 °C, CO:H2 = 1:2, gas hourly space velocity = 3500 h−1). A catalyst with exposed Fe particles on the outside of the Pod-Fe (FeOx/Pod-Fe) catalyst showed a selectivity of light olefins of 42%, but had a significantly lower stability due to the agglomeration of Fe nanoparticles and carbon deposition. These results indicated that the graphene shell of Pod-Fe played an important role in protecting the Fe particles and provided a rational way to enhance the activity and stability of Fe-based catalysts in high temperature reactions.

Direct conversion of syngas into hydrocarbons with high selectivity remains a challenge. Herein, we report the synthesis of a core–shell-structured catalyst constituting Cr-Zn oxide as the core and SAPO-34 as the shell for the conversion of syngas into hydrocarbons with high selectivity. A SiO2 layer was sandwiched between the core and the shell to prevent damage to the core during shell synthesis. Furthermore, the intermediate SiO2 layer acted as a Si source for the formation of the shell. The prepared catalyst displayed considerably higher selectivity toward the production of C2–C4 hydrocarbons (66.9%) than that of methanol and methane. The findings show the potential of the prepared core–shell-structured catalyst in the one-step production of hydrocarbons, such as liquefied petroleum gas, from syngas. However, further optimization of the catalyst is necessary to achieve higher performance.

Catalysis, as a key and enabling technology, plays an increasingly important role in fields ranging from energy, environment and agriculture to health care. Rational design and synthesis of highly efficient catalysts has become the ultimate goal of catalysis research. Thanks to the rapid development of nanoscience and nanotechnology, and in particular a theoretical understanding of the tuning of electronic structure in nanoscale systems, this element of design is becoming possible via precise control of nanoparticles’ composition, morphology, structure and electronic states. At the same time, it is important to develop tools for in situ characterization of nanocatalysts under realistic reaction conditions, and for monitoring the dynamics of catalysis with high spatial, temporal and energy resolution. In this review, we discuss confinement effects in nanocatalysis, a concept that our group has put forward and developed over several years. Taking the confined catalytic systems of carbon nanotubes, metal-confined nano-oxides and 2D layered nanocatalysts as examples, we summarize and analyze the fundamental concepts, the research methods and some of the key scientific issues involved in nanocatalysis. Moreover, we present a perspective on the challenges and opportunities in future research on nanocatalysis from the aspects of: (1) controlled synthesis of nanocatalysts and rational design of catalytically active centers; (2) in situ characterization of nanocatalysts and dynamics of catalytic processes; (3) computational chemistry with a complexity approximating that of experiments; and (4) scale-up and commercialization of nanocatalysts.

Rhenium (Re), a high-performance engineering material with a hexagonal close-packed (hcp) structure, remains stable even under pressures of up to 250 GPa and at temperatures up to its melting point (3453 K). We observed here that Re atoms self-assembled, within the confined space of carbon nanotubes (CNTs) with a diameter of

To tailor the catalytic activities of metal catalysts at will to achieve efficient conversion in chemical processes remains a challenge, particularly for noble metals, such as Pt. We demonstrate herein that encapsulation within the carbon nanotube (CNT) channels with a diameter of 1.0-1.5 nm not only allows restriction of the size of Pt nanoclusters around 1.0 nm but also enables modulating of the Pt species at the active reduced states through host guest interaction. The encapsulated Pt is protected from oxygen under reaction conditions in toluene oxidation up to 200 degrees C, as unveiled by in situ X-ray absorption spectroscopy and density functional theory calculations. As a result, the encapsulated Pt clusters deliver a remarkably higher activity and stability than the clusters located on the open surfaces of the CNT exterior walls and carbon black support, although the latter are much more accessible to reactants. This characteristic of the CNT channels can be explored to tune the properties of other metal catalysts for oxidation reactions.

N-doped graphene used as an efficient electron donor of iron catalysts for CO hydrogenation can achieve a high selectivity of around 50% for light olefins, significantly superior to the selectivity of iron catalysts on conventional carbon materials, e.g. carbon black with a selectivity of around 30% at the same reaction conditions.

The ring currents by the axial component of B0 depend on the semiconducting or metallic properties of CNTs and hence determine the overall magnetic responses and the aromatic characters., Ring current is a fundamental concept to understand the nuclear magnetic resonance (NMR) properties and aromaticity for conjugated systems, such as carbon nanotubes (CNTs). Employing the recently developed gauge including projector augmented wave (GIPAW) method, we studied the ring currents of CNTs systematically and visualized their distribution. The ring current patterns are determined by the semiconducting or metallic properties of CNTs. The discrepancy is mainly caused by the axial component of external magnetic fields, whereas the radial component induced ring currents are almost independent of the electronic structures of CNTs, where the intensities of the ring currents are linearly related to the diameters of the CNTs. Although the ring currents induced by the radial component are more intense than those by the axial component, only the latter determines the overall NMR responses and aromaticity of the CNTs as well. Furthermore, the semiconducting CNTs are more aromatic than their metallic counterparts due to the existence of delocalized ring currents on the semiconducting CNTs. These fundamental features are of vital importance for the development of CNT-based nanoelectronics and applications in magnetic fields.

Carbon dioxide transformation to fuels or chemicals provides an attractive approach for its utilization as feedstock and its emission reduction. Herein, we report a gas-phase electrocatalytic reduction of CO 2 in an electrolytic cell, constructed using phosphoric acid-doped polybenzimidazole (PBI) membrane, which allowed operation at 170 °C. Pt/C and PtMo/C with variable ratio of Pt/Mo were studied as the cathode catalysts. The results showed that PtMo/C catalysts significantly enhanced CO formation and inhibited CH 4 formation compared with Pt/C catalyst. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed that most Mo species existed as MoO 3 in PtMo/C catalysts and the interaction between Pt and MoO x was likely responsible for the enhanced CO formation rate although these bicomponent catalysts in general had a larger particle size than Pt/C catalyst.

Commercial production of vinyl chloride from acetylene relies on the use of HgCl2 as the catalyst, which has caused severe environmental problem and threats to human health because of its toxicity. Therefore, it is vital to explore alternative catalysts without mercury. We report here that N-doped carbon can catalyze directly transformation of acetylene to vinyl chloride. Particularly, N-doped high surface area mesoporous carbon exhibits a rather high activity with the acetylene conversion reaching 77% and vinyl chloride selectivity above 98% at a space velocity of 1.0 mL·min−1·g −1 and 200 °C. It delivers a stable performance within a test period of 100 h and no obvious deactivation is observed, demonstrating potentials to substitute the notoriously toxic mercuric chloride catalyst.

Conversion of CO2 using renewable hydrogen to produce valuable chemicals has recently become highly attractive. Light olefins are important basic monomers for the production of various commodities. This work developed a bifunctional catalyst composed of ZnO-Y2O3 oxide and SAPO-34 zeolite, which catalyzes the selective hydrogenation of CO2 to light olefins with a selectivity in hydrocarbons reaching 83.9% at a conversion of 27.6% at 390 °C. The obtained results demonstrated that CO2 conversion and product distribution are strongly dependent on the oxide composition and structure. This new bimetallic oxide catalyst appears promising for further development of CO2 conversion to other valuable chemicals.

Large magnetic shielding has been experimentally observed on certain organic molecules, regardless of their intrinsically different chemical natures, when they are confined within the carbon nanotubes. We investigated the underlying physics of the shielding effect by employing a series of density functional theory calculations on various molecule-confined-in-CNT systems. Particularly, the effects of the intermolecular interaction and the ring current of the CNTs on the chemical shifts of the confined molecules were investigated in detail. The results reveal that the changes in chemical shift mainly originate from the magnetic shielding induced by the delocalized g electrons. Electronic structure analysis for nonbonded interactions of host guest and guest guest indicated that this intermolecular interaction effect on chemical shift is significant for the polarizable molecules. Thus, the NMR responses of the molecules confined in CNTs are different from those of the molecules in other confining environments. Our study thus suggested that the chemical shift can be used as a probe to distinguish the molecules inside and outside of the CNT channels, as well as the type of CNTs (such as metallic and semiconducting).

A C–SiC composite with a thin layer of carbon surrounding the SiC substrate has been produced by the reaction of SiC with CCl4. The pore structures, graphitization levels and the chemical compositions can be finely modulated by the synthesis temperature, and atmosphere. A higher synthesis temperature accelerates the chlorination rate, increases the thickness of carbon layers and enhances their graphitization. Mesopores can be generated in C–SiC composites in comparison to predominant micropores in commercial activated carbon (AC), particularly in the presence of reactive atmosphere such as CO2 and NH3. Furthermore, with cofeeding of NH3 with CCl4, N heteroatoms can be incorporated into the carbon layer and the N content varies in a range of 4.7–9.5 at.%, depending on the synthesis conditions. Both increased fraction of mesopores and their sizes, as well as N doping facilitate significantly hydrogenation of 4-carboxybenzaldehyde. The activity of Pd catalyst supported on N-doped C–SiC is five times that on commercially used AC under the same conditions.

A versatile wet chemistry method is developed for filling of subnanometer sized metal particles in carbon nanotubes with a diameter smaller than 1.5 nm. As an example, we showed that a confined bi-component Pd-V catalyst exhibit a higher benzene hydroxylation activity compared with that within multi-walled carbon nanotubes.

Chainmail for catalysts: a catalyst with iron nanoparticles confined inside pea-pod-like carbon nanotubes exhibits a high activity and remarkable stability as a cathode catalyst in polymer electrolyte membrane fuel cells (PEMFC), even in presence of SO(2). The approach offers a new route to electro- and heterogeneous catalysts for harsh conditions.

The interaction of an Fe atom, an Fe dimer, a one-dimensional Fe nanowire, and an FeO nanowire with a single-walled armchair carbon nanotube (CNT) (8, 8) is investigated using density functional theory calculations. The results show that for all iron species the bonding with the outside wall of the CNT is stronger than that with the inside wall. Analysis of the electron distribution of the CNT shows that the curvature of the CNT induces a significant electron disparity at the inside and outside regions and more electrons are distributed on the outer surface. The properties of the frontier orbitals of the CNT are studied, and the results show that the highest occupied molecular orbital and lowest unoccupied molecular orbital are mainly located outside the tube, which may account for the in- and out-dependent interactions of Fe species with the CNT surface and hence different chemical reactivities of CNT-loaded metals.

The effects of manganese and potassium on the structural and morphological properties, phase compositions and CO adsorption behavior of the CNT-confined FeN catalyst were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fe-57 Mossbauer effect spectroscopy (MES) and CO temperature-programmed desorption (TPD). The results suggested that the presence of manganese helps retain nitrogen in cubic FeCxN1-x and facilitates CO adsorption. The selectivity to (C2C4=)-C-= light olefins is enhanced over Mn(1.0 wt%)/FeN/CNT although the activity decreases within the loading range of 0.5-2.0 wt% for Mn. Although further promotion with K could improve the activity slightly, the selectivity to light olefins decreases. At the same time, the addition of potassium enhanced the water gas shift activity and shifted the selectivity to heavy hydrocarbons (C5+), similar to the conventional reduced iron catalysts. (C) 2011 Elsevier B. V. All rights reserved.

Hydrogenation of benzaldehyde is a typical consecutive reaction, since the intermediate benzyl alcohol is apt to be further hydrogenated. Here we demonstrate that the selectivity of benzyl alcohol can be tuned via functionalization of carbon nanotubes (CNTs), which are used as the support of Pd. With the original CNTs, the selectivity of benzyl alcohol is 88% at a 100% conversion of benzaldehyde. With introduction of oxygen-containing groups onto CNTs, it drops to 27%. In contrast, doping CNTs with N atoms, the selectivity reaches 96% under the same reaction conditions. The kinetic study shows that hydrogenation of benzyl alcohol is significantly suppressed, which can be attributed to weakened adsorption of benzyl alcohol. This is most likely related to the modified electronic structure of Pd species via interaction with functionalized CNTs, as shown by XPS characterization.

Adsorption of 13C-enriched methanol in multiwalled carbon nanotubes (MWNTs) was systematically studied under well-controlled environment by 13C MAS NMR. The results of variable-pressure experiments indicate that the endohedral adsorption of methanol in carbon nanotubes (CNTs) is preferential over the exohedral adsorption. The exohedral adsorption does not occur until the endohedral adsorption saturates. The 13C chemical shift of endohedral methanol exhibits a large upfield shift due to the strong spatial diamagnetic shielding effect induced by the delocalized electrons of nanotubes under the influence of external magnetic field. The exohedral methanol is also shielded, but to a lesser extent. DFT calculations support these experimental results. The 13C spin–lattice relaxation times, T1, of endohedral and exohedral methanol were also measured, and they have different vapor pressure dependence at room temperature. Furthermore, variable-temperature experiments suggest that methanol molecules inside CNTs may ...

A coordinatively unsaturated single iron site confined in a graphene matrix shows an ultrahigh activity for catalytic oxidation., Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN4 centers in the graphene matrix. The atomic structure of FeN4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.

Nitrogen-doped graphene (N-graphene) was reported to exhibit a good activity experimentally as an electrocatalyst of oxygen reduction reaction (ORR) on the cathode of fuel cells under the condition of electropotential of ∼0.04 V (vs. NHE) and pH of 14. This material is promising to replace or partially replace the conventionally used Pt. In order to understand the experimental results, ORR catalyzed by N-graphene is studied using density functional theory (DFT) calculations under experimental conditions taking the solvent, surface adsorbates, and coverages into consideration. Two mechanisms, i.e., dissociative and associative mechanisms, over different N-doping configurations are investigated. The results show that N-graphene surface is covered by O with 1/6 monolayer, which is used for reactions in this work. The transition state of each elementary step was identified using four different approaches, which give rise to a similar chemistry. A full energy profile including all the reaction barriers shows that the associative mechanism is more energetically favored than the dissociative one and the removal of O species from the surface is the rate-determining step.

A nanomaterial, folate and iron difunctionalized multiwall carbon nanotube (FA-MWCNT@Fe), has been synthesized by conjugating folate and iron nanoparticles with oxidized multi-walled carbon nanotubes, and applied as a dual-targeted drug nanocarrier to deliver doxorubicin into HeLa cells with the assistance of an external magnetic field. The prepared FA-MWCNT@Fe was characterized by X-ray diffraction, transmission electron microscopy and infrared spectroscopy. This nanocarrier has a sufficient load capacity (doxorubicin/FA-MWCNT@Fe, 32 μg/mg) and a prolonged release property controlled by near infrared radiation. It also demonstrated both biologically (active) and magnetically (passive) targeting capabilities toward HeLa cells in vitro with ca. 6-fold higher delivery efficiency of doxorubicin than free doxorubicin.

Theoretical studies predicted that doping graphene with nitrogen can tailor its electronic properties and chemical reactivity. However, experimental investigations are still limited because of the lack of synthesis techniques that can deliver a reasonable quantity. We develop here a novel method for one-pot direct synthesis of N-doped graphene via the reaction of tetrachloromethane with lithium nitride under mild conditions, which renders fabrication in gram scale. The distinct electronic structure perturbation induced by the incorporation of nitrogen in the graphene network is observed for the first time by scanning tunnelling microscopy. The nitrogen content varies in the range of 4.5−16.4%, which allows further modulation of the properties. The enhanced catalytic activity is demonstrated in a fuel cell cathode oxygen reduction reaction with respect to pure graphene and commercial carbon black XC-72. The resulting N-doped materials are expected to broaden the already widely explored potential applicatio...

A theoretical study combining first-principles and Monte Carlo simulations has been carried out to investigate the interactions of H2 and CO molecules with carbon nanotube (CNT) surfaces. The results show that there are stronger interactions of both H2 and CO with the interior nanotube surface than with the exterior surface. In addition, CO interacts more strongly with CNT surfaces than H2. This can be explained by the nature of the molecules and the different electronic properties of the concave and convex surfaces of CNTs formed by graphene layers. As a result, syngas molecules are enriched inside CNTs and the enrichment generally becomes greater in smaller nanotubes. Furthermore, the ratio of CO/H2 inside CNTs increases with respect to the composition of syngas in the exterior gas phase. The enriched reactants and altered CO/H2 ratio inside nanotubes could be beneficial for the reaction rate and lead to modification of the product selectivity.

Ethanol is considered as a potential alternative synthetic fuel to be used in automobiles or as a potential source of hydrogen for fuel cells. In this paper we first undertake a brief overview of the catalyst development for syngas conversion to C-2 oxygenates over Rh-based catalysts, mainly on the effects of various additives and supports on the activity and selectivity. Then we investigated the effects of carbon materials, which have been rarely studied as supports for Rh-based catalysts in this process. For example, rather well graphitized carbon black, very high surface area CMK-3 and activated carbon (AC) were compared to carbon nanotubes (CNTs), which exhibits a medium level surface area with well defined nanochannels. The CNT-supported catalyst shows a highest overall activity and yield of C-2 oxygenates compared to the other carbon-supported catalysts. The catalysts are characterized by N-2 adsorption-desorption, CO chemisorption, TEM, XRD and TPD. The graphitized structure combined with the tubular morphology of CNTs likely play an important role. (C) 2009 Elsevier B.V. All rights reserved.

Following our previous findings that confinement within carbon nanotubes (CNTs) can modify the redox properties of encapsulated iron oxides, we demonstrate here how this can affect the catalytic reactivity of iron catalysts in Fischer-Tropsch synthesis (FTS). The investigation, using in situ XRD under conditions close to the reaction conditions, reveals that the distribution of iron carbide and oxide phases is modulated in the CNT-confined system. The iron species encapsulated inside CNTs prefer to exist in a more reduced state, tending to form more iron carbides under the reaction conditions, which have been recognized to be essential to obtain high FTS activity. The relative ratio of the integral XRD peaks of iron carbide (Fe(x)C(y)) to oxide (FeO) is about 4.7 for the encapsulated iron catalyst in comparison to 2.4 for the iron catalyst dispersed on the outer walls of CNTs under the same conditions. This causes a remarkable modification of the catalytic performance. The yield of C5+ hydrocarbons over the encapsulated iron catalyst is twice that over iron catalyst outside CNTs and more than 6 times that over activated-carbon-supported iron catalyst. The catalytic activity enhancement is attributed to the effect of confinement of the iron catalyst within the CNT channels. As demonstrated by temperature-programmed reduction in H2 and in CO atmospheres, the reducibility of the iron species is significantly improved when they are confined. The ability to modify the redox properties via confinement in CNTs is expected to be of significance for many catalytic reactions, which are highly dependent on the redox state of the active components. Furthermore, diffusion and aggregation of the iron species through the reduction and reaction have been observed, but these are retarded inside CNTs due to the spatial restriction of the channels.

The combination of Pt2+, benzoquinone and NaNO2 forms an electron-transfer chain, which leads to the oxidation of methane by O2 in CF3COOH aqueous solution. The overall turnover number per hour (TOF) of methane at 120 °C is 0.5 h−1, however, only about one fourth (23%) of methane is converted to the desired product of methanol in the formation of CF3COOCH3. The over-oxidation of methane to CO2, over the catalyst with the Pt2+ species immobilized via 2,2′-bipyridyl as a ligand on the silica substrate, is depressed distinctly. Under the same conditions, the conversion to methanol dominates, and no CO2 is observed, on account of the over-oxidation of methane, as confirmed by the isotope experiment.

Carbon nanotubes (CNTs) have well-defined hollow interiors and exhibit unusual mechanical and thermal stability as well as electron conductivity1. This opens intriguing possibilities to introduce other matter into the cavities2,3,4,5, which may lead to nanocomposite materials with interesting properties or behaviour different from the bulk6,7,8. Here, we report a striking enhancement of the catalytic activity of Rh particles confined inside nanotubes for the conversion of CO and H2 to ethanol. The overall formation rate of ethanol (30.0 mol mol−1Rh h−1) inside the nanotubes exceeds that on the outside of the nanotubes by more than an order of magnitude, although the latter is much more accessible. Such an effect with synergetic confinement has not been observed before in catalysis involving CNTs. We believe that our discovery may be of a quite general nature and could apply to many other processes. It is anticipated that this will motivate theoretical and experimental studies to further the fundamental understanding of the host–guest interaction within carbon and other nanotube systems.

This study reports the poisoning effect of co-existing nitrogen on hydrogen permeation through Pd composite membranes, consisting of thin Pd layerssupportedon-Al2O3 hollowfibers.Hydrogenpermeationofthecompositemembraneswasmeasuredattemperaturesof623‐773Kforpure gas permeation in sequence of hydrogen, nitrogen and hydrogen and for mixture gas separation of equimolar H2/N2. The composite membranes were defect-free and gave high hydrogen permeance of 31.2m 3 /m 2 hbar at 773K. However, when the H2 activated composite membranes were exposed to nitrogen for a certain time, the followed hydrogen permeance decreased in comparison with the original value. The degree of decrease increased with decreasing temperature and with exposure time. Furthermore, when the composite membranes were exposed to the mixture feed of equimolar H2/N2 with certain total flow rate at temperatures of 673‐723K, the hydrogen flux on the permeate side kept stable only for several 100min then decreased gradually to some extent. And significant reduction could be obtained during the followed pure hydrogen permeance test in comparison with the original value for the fresh membranes. Fortunately, no additional defects were formed on the Pd layers during these processes and the deactivations of the composite membranes were reversible. A certain-time hydrogen treatment at 773K was sufficient to regenerate the deactivated membranes. The blocking of the active sites on Pd surface for hydrogen diffusion by the formed nitrogen-containing species (NHx, x=0‐2) was responsible for the deactivation of the membranes in the suggested deactivation mechanism.

Pod-like carbon nanotube with encapsulated iron particles (Pod-Fe) was used as a well-defined model to study the electronic interaction between carbon shells and the iron particles by scanning transmission X-ray microscopy (STXM)., The electronic interaction of a catalyst and its support is of vital importance to its catalytic performance. However, it is still a great challenge to directly probe the interaction due to the lack of well-defined models and efficient technical means. In this study, we report that pod-like carbon nanotubes with encapsulated iron particles (Pod-Fe) and scanning transmission X-ray microscopy (STXM) can be used as an ideal model and technique to study the electronic interaction between carbon shells and iron particles. The chemical imaging and spectroscopy of Pod-Fe by STXM show that the local electronic structures at C K-edge near edge (π*) of carbon shells can be significantly modified by the encapsulated iron particles, which promotes the adsorption of oxygen-containing species, and thereby further modifies the electronic structure (π* and σ*) of the carbon shells. Moreover, computed X-ray absorption near edge structure spectra (XANES) confirmed the electronic modifications of carbon shells by the encapsulated iron particles. The present study provides a direct evidence of electronic interactions with simultaneously collected images and spectra, which can promote the understanding towards the nature of active sites and supports.

Synthesis of aluminosilicate MWW zeolite with variable Si/Al ratios from deboronated ERB-1 zeolite through a process of structural conversion has been studied and the obtained material has been characterized in detail. Incorporation of aluminum species into the framework of deboronated ERB-1 zeolite and the acidity of calcined MWW zeolite have been confirmed by a number of physicochemical techniques. Aluminum species in the lamellar MWW zeolite precursor are not thermally stable, and partial dealumination takes place during the calcination process. MWW zeolite shows strong Bronsted acidity, and the amount of Bronsted acid sites is closely related with the amount of framework aluminum in MWW zeolite. Disproportionation of toluene was carried out over MWW zeolite with different Si/Al ratios, and the catalytic performance has been correlated with the Bronsted acidity of MWW zeolite.

An increasing number of experimental studies have demonstrated that metal or metal oxide nanoparticles confined inside carbon nanotubes (CNTs) exhibit different catalytic activities with respect to the same metals deposited on the CNT exterior walls, with some reactions enhanced and others hindered. In this article, we describe the concept of confinement energy, which enables prediction of confinement effects on catalytic activities in different reactions. Combining density functional theory calculations and experiments by taking typical transition metals such as Fe, FeCo, RhMn, and Ru as models, we observed stronger strains and deformations within the CNT channels due to different electronic structures and spatial confinement. This leads to downshifted d-band states, and consequently the adsorption of molecules such as CO, N2, and O2 is weakened. Thus, the confined space of CNTs provides essentially a unique microenvironment due to the electronic effects, which shifts the volcano curve of the catalytic activities toward the metals with higher binding energies. The extent of the shift depends on the specific metals and the CNT diameters. This concept generalizes the diverse effects observed in experiments for different reactions, and it is anticipated to be applicable to an even broader range of reactions other than redox of metal species, CO hydrogenation, ammonia synthesis and decomposition discussed here.

For an effective operation of a membrane reactor in comparison with a conventional fixed-bed reactor, the kinetic compatibility of hydrogen production and its removal is essential. The aim of this work is to provide an estimation of the membrane area needed for the extraction of the hydrogen which is produced at a defined gas hourly space velocity (GHSV) in steam reforming of methane (SR). The SR was studied in a fixed-bed reactor using a conventional Ni-catalyst for evaluating the kinetic parameters. The conversion of methane was simulated by a one-dimensional, non-isothermal reactor model and compared with the experimental results. Hydrogen conducting Pd-membranes were prepared by electroless plating, and the hydrogen permeation through these membranes was determined. The analysis performed can provide an estimation for the design of a catalytic membrane reactor.

The single gas H-2 and N-2 permeability of a 4 mu m thick dense fcc-Pd66Cu34 layer has been studied between room temperature and 5 10 degrees C and at pressure differences up to 400 kPa. Above 50 degrees C the H-2 flux exhibits an Arrhenius-type temperature dependence with J(H2) = (5.2 +/- 0.3) mol m(-2) s(-1) exp[(-21.3 +/- 0.2) kJ mol(-1)/((RT)-T-.)]. The hydrogen transport rate is controlled by the bulk diffusion although the pressure dependence of the H-2 flux deviates slightly from Sieverts' law. A sudden increase of the H-2 flux below 50 degrees C is attributed to embrittlement.

Homogeneous dispersion of metal oxide nanoparticles was achieved on carbon nanotubes (CNTs) even with a very small amount of surface oxygen functional groups (SOFGs) aided by using ethylene glycol (EG) and sodium hydroxide during the process. Similar particle size distributions were obtained for iron deposited on CNTs containing various amounts of SOFGs. We proposed that formation of hydrogen bonds between EG on the CNT surface and sodium hydroxide is likely responsible, which creates precipitating sites for iron ions on the CNT surface. This facile method is expected to find applications not only for catalysis but also in the fields such as sensors and magnetic materials in particular where a perfect sp2 hybridized carbon structure is preferred.