Search

Non-oxidative conversion of methane to olefins, aromatics and hydrogen (MTOAH) has been reported recently over metal single sites such as iron and platinum. The reaction was proposed to involve catalytic activation of methane followed by gas phase C−C coupling of methyl radicals. This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species (denoted as Fe-reactor). Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2 (ethane, ethylene and acetylene) and 31.8% toward BTX (benzene, toluene and xylene), respectively. The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene, which provides an additional route of methane activation apart from catalytic activation.

Boron-modified ZrO2 (B-ZrO2) was synthesized under various pH values (9, 10, and 11) and used as the supports of PtSn catalysts (PtSn/B-ZrO2-x) for non-oxidative dehydrogenation of propane. The NH3-TPD and pyridine IR show that only Lewis acid is present and the acid strength increases with the synthesis pH. PtSn/B-ZrO2-10 exhibits the best catalytic performance with an initial propane conversion of 36% and a deactivation rate constant (kd) of 0.0127 h−1. The XPS results indicate that the electronic properties of Pt and SnOx are affected not only by their interaction but also by the interaction with support. After a careful analysis of the oxygen storage capacity and activity in CO oxidation, it is hypothesized that the interaction between Pt and Sn becomes stronger following the order: PtSn/B-ZrO2-9

The effect of the Al2O3 structure on the performance of Pt/Ga/Al2O3 catalysts is investigated for the direct dehydrogenation of propane. The study unveils that the structure of Al3+ determines the bulk structure of catalysts, particularly a high content of coordinatively unsaturated Al3+ sites (penta-coordinated Al3+, denoted as Al3+penta) could lead to a remarkably improved dehydrogenation activity of the catalyst. The bulk characterization reveals that the sufficient amount of Al3+penta in Al2O3 benefit the dispersion of Pt and Ga2O3 on the Al2O3 support. At the same time, TPR results reveal that the presence of Pt facilitates the reduction of Ga2O3, likely due to the hydrogen spillover between the well dispersed Pt and Ga2O3, which consequently enhances the synergistic function between Pt and Ga2O3 in the dehydrogenation of propane. Recyclability tests demonstrate that the dehydrogenation activity stabilizes after three cycles over the Pt/Ga/Al2O3 catalyst.

Oxide-Zeolite (OX-ZEO) bifunctional catalyst design concept has been exemplified in several processes to direct conversion syngas to value-added chemicals and fuels such as mixed light olefins, ethylene, aromatics and gasoline. Herein we demonstrate that the product can be steered toward liquefied petroleum gas (LPG) with a selectivity up to 89% in hydrocarbons especially propane selectivity reaching 80% at CO conversion of 63% using ZnCrOx-H-SSZ-39 catalyst. Interestingly, the quantity of the acid sites of SSZ-39 does not influence obviously the hydrocarbon distribution but the strength is crucial for selective formation of propane. This finding provides an alternative route of LPG synthesis from a variety of carbon resources via syngas.

Aromatics are important basic chemicals. However, direct conversion of syngas via the conventional Fischer-Tropsch synthesis produces little aromatics. We presented herein that a bifunctional composite of ZSM-5 in combination with ZnCrOx catalyzes syngas conversion to aromatics. Particularly, ZSM-5 crystals with a sheet-like morphology can enhance significantly the aromatization activity. The lower length ratio of the b/a axes of the crystals, the more aromatics form but without influencing the selectivity of small molecules such as CH4 and C2–C4. Since the acid properties and the Al chemical environment were not altered while the morphology changed, the enhanced aromatic selectivity is likely attributed to the favored diffusion of aromatics in these sheet-like crystals.

Boron had been introduced into the structure of carbon material (BC), which was used as the support of Pd catalyst for hydrogenation of 4-carboxybenzaldehyde (4-CBA). The physical properties and chemical composition of the support and corresponding catalyst were characterized by N2 adsorption–desorption, Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), element analysis (EA), high-resolution transmission electron microscopy (HRTEM), CO-pulse chemisorption and X-ray photoelectron spectroscopy (XPS). The results demonstrate that Pd/BC catalyst exhibits a superior activity and good stability due to the more uniform dispersion of Pd nanoparticles, the presence of mesoporous structure and the enhanced interaction between Pd nanoparticles and the support, compared to carbon and N-doped carbon supported Pd catalysts (Pd/C and Pd/NC, respectively).

Carbon nanotubes (CNTs) have shown as unique nanoreactors to tune the catalytic activity of confined nano-catalysts. Here we report that the catalytic performance of molybdenum carbide nanoparticles (MoCx NPs) for the hydrogen evolution reaction (HER) process can be enhanced by encapsulation within single-walled carbon nanotubes (SWNTs) with a diameter of 1-2 nm. The catalyst with MoCx NPs located on the interior surface of SWNTs (MoCx@SWNTs) exhibits a lower onset over-potential and a smaller Tafel slope than the one with MoCx NPs attached on the exterior surface (MoCx/SWNTs). This is likely attributed to the much smaller particle size and the more reduced states of the confined MoCx NPs, as well as the larger specific surface area of MoCx@SWNTs compared with MoCx/SWNTs. In addition, the electronic structure of the confined MoCx NPs might be modified by the confinement effects of SWNTs, and hence the adsorption free energy of H atoms on the confined MoCx NPs, which could also contribute to their higher performance. These results suggest that the SWNTs can be further explored for constructing novel catalysts with beneficial catalytic performance.

Nonoxidative conversion of ethane to ethylene and/or BTX (benzene, toluene , and xylene) suffers rapid deactivation due to coke deposition. We report here the effects of phosphorus modification on the stability and activity of Mo/ZSM5 for nonoxidative conversion of ethane. The results show that the ethylene and BTX yield and stability are significantly enhanced upon modification with 2.5 wt.% P. NH 3 TPD, pyridine FTIR, 1H MAS NMR, 27Al MAS NMR, 31P MAS NMR, 129 Xe NMR, XPS, UV–visible diffuse reflectance spectra (UV–vis DRS), and nitrogen physisorption were carried out to understand the effects of P on the structure of Mo/ZSM5 and its correlation with catalytic performance. The presence of P reduces the acid strength and density, changes the channel system of ZSM5 by forming thermally stable SAPO-like interfaces with the framework Al, and improves the dispersion of molybdenum . Rapid deactivation still occurs on Mo/ZSM5 with 1 wt.% P due to the existence of denser silanol groups, more isolated Mo species, and reduced aperture size with little change in effective micropore volume. A higher P loading (2.5 wt.%) leads to less dense silanol groups and less reduced but stable molybdenum species, and simultaneously reduces channel diameter and internal volume. Consequently, the ethylene selectivity is enhanced and the formation of coke precursors is restricted, resulting in improved stability.

Nitrogen doping has been proved to be an effective way to modify the properties of graphene and other carbon materials. Herein, we explore a composite with nitrogen doped carbon overlayers wrapping SiC substrate as a support for Ni (Ni/CN-SiC) and evaluate its effects on the methanation activity. The results show that both the activity and stability of Ni are enhanced. Characterization with STEM, XRD, XPS, Raman and H2-TPR indicates that nitrogen doping generates more defects in the carbon overlayers, which benefit the dispersion of Ni. Furthermore, the reduction of Ni is facilitated.

NC@SiC prepared by a facile pyrolysis method was used as the support of Pd catalyst for the hydrogenation of 4-carboxybenzaldehyde. The structure of Pd/NC@SiC was characterized by N2 adsorption-desorption, ICP-OES, SEM, HRTEM and XPS. The Pd/NC@SiC catalyst showed superior activity compared with Pd/SiC due to its hierarchically mesoporous and microporous structure and the synergistic effect between Pd and N-doped carbon layer. In addition, Pd/NC@SiC also exhibited a good durability under high temperature and high pressure H2, which was attributed to its highly dispersed Pd nanoparticles stabilized by the N-doped carbon structure.

The catalytic activity of metal catalysts can be modulated by confinement within the channels of carbon nanotubes (CNTs). Here, we show that the product distribution of cinnamaldehyde hydrogenation can be modified by confinement of Ru nanoparticles in CNTs. A catalyst composed of Ru nanoparticles dispersed on the exterior walls of CNTs gave hydrocinnamaldehyde as product. In contrast, confinement of the Ru nanoparticles within CNT channels facilitated hydrogenation of C=O bonds and complete hydrogenation, and both cinnamyl alcohol and hydrocinnamyl alcohol formed in addition to hydrocinnamaldehyde. High-resolution transmission electron microscopy, Raman spectroscopy, hydrogen temperature-programmed reduction, and hydrogen temperature-programmed desorption were used to investigate the characteristics of the catalysts. The results indicate that the different interactions between the confined Ru nanoparticles and the exterior and interior walls of the CNTs, as well as spatial restriction and enrichment within the narrow channels likely play important roles in modulation of the product distribution.

Acetylene hydrochlorination is an important coal-based technology for production of vinyl chloride, the monomer of one of the world mostly used plastics. Despite of the great potentials demonstrated for carbon-based catalysts to replace the toxic mercury chloride, the stability and the deactivation mechanism are rarely discussed, which is essential for real applications. Herein, we present a detailed study on the deactivation mechanism of nitrogen doped carbon based catalyst in acetylene hydrochlorination. The results show that the deactivation was likely caused by the carbon-like deposition over the catalyst, which can be regenerated with high temperature NH 3 treatment.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.