Showing papers on "Catalyst support published in 2010"
TL;DR: Different aspects of CNT synthesis and growth mechanism are reviewed in the light of latest progresses and understandings in the field, and existing problems and challenges of the process are addressed with future directions.
Abstract: This review article deals with the growth mechanism and mass production of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). Different aspects of CNT synthesis and growth mechanism are reviewed in the light of latest progresses and understandings in the field. Materials aspects such as the roles of hydrocarbon, catalyst and catalyst support are discussed. Many new catalysts and new carbon sources are described. Growth-control aspects such as the effects of temperature, vapor pressure and catalyst concentration on CNT diameter distribution and single- or multi-wall formation are explained. Latest reports of metal-catalyst-free CNT growth are considered. The mass-production aspect is discussed from the perspective of a sustainable CNT technology. Existing problems and challenges of the process are addressed with future directions.
1,235 citations
TL;DR: An analysis of previous calorimetry data for silver nanoparticles on magnesium oxides and cerium oxide surfaces is presented and it is shown that nanoparticles smaller than 1000 atoms are bound much more strongly to reduced Cerium oxide.
Abstract: The energies of silver (Ag) atoms in Ag nanoparticles supported on different cerium and magnesium oxide surfaces, determined from previous calorimetric measurements of metal adsorption energies, were analyzed with respect to particle size. Their stability was found to increase with particle size below 5000 atoms per particle. Silver nanoparticles of any given size below 1000 atoms had much higher stability (30 to 70 kilojoules per mole of silver atoms) on reduced CeO2(111) than on MgO(100). This effect is the result of the very large adhesion energy (approximately 2.3 joules per square meter) of Ag nanoparticles to reduced CeO2(111), which we found to be a result of strong bonding to both defects and CeO2(111) terraces, apparently localized by lattice strain. These results explain the unusual sinter resistance of late transition metal catalysts when supported on ceria.
742 citations
TL;DR: In this article, the nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, increased support/catalyst chemical binding (or "tethering"), and catalyst particle electronic structure modification, which enhances intrinsic catalytic activity.
Abstract: Insufficient catalytic activity and durability are key barriers to the commercial deployment of low temperature polymer electrolyte membrane (PEM) and direct-methanol fuel cells (DMFCs). Recent observations suggest that carbon-based catalyst support materials can be systematically doped with nitrogen to create strong, beneficial catalyst-support interactions which substantially enhance catalyst activity and stability. Data suggest that nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: 1) modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, 2) increased support/catalyst chemical binding (or “tethering”), which results in enhanced durability, and 3) catalyst nanoparticle electronic structure modification, which enhances intrinsic catalytic activity. This review highlights recent studies that provide broad-based evidence for these nitrogen-modification effects as well as insights into the underlying fundamental mechanisms.
584 citations
TL;DR: Graphene nanoplatelets have been used as a catalyst support for platinum nanoparticles for oxygen reduction reactions in proton exchange membrane fuel cells as mentioned in this paper, and a full cell was constructed with platinum loaded nitrogen doped graphene nanoplatelet and the results have been compared with the results obtained with the conventional chemical reduction technique.
Abstract: Graphene nanoplatelets have been synthesized by thermal exfoliation of graphitic oxide and nitrogen doped graphene nanoplatelets have been obtained by nitrogen plasma treatment. Graphene nanoplatelets and nitrogen doped graphene nanoplatelets have been used as a catalyst support for platinum nanoparticles for oxygen reduction reactions in proton exchange membrane fuel cells. Platinum nanoparticles were dispersed over these support materials using the conventional chemical reduction technique. The morphology and structure of the graphene based powder samples were studied using X-ray diffraction, Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A full cell was constructed with platinum loaded nitrogen doped graphene nanoplatelets and the results have been compared with platinum loaded graphene nanoplatelets. A maximum power density of 440 and 390 mW cm−2 has been obtained with platinum loaded nitrogen doped graphene and platinum loaded graphene nanoplatelets as ORR catalysts respectively. Nitrogen plasma treatment created pyrrolic nitrogen defects, which act as good anchoring sites for the deposition of platinum nanoparticles. The improved performance of fuel cells with N-G as catalyst supports can be attributed to the increased electrical conductivity and improved carbon–catalyst binding.
580 citations
TL;DR: In this paper, the role of surface chemistry in carbon catalysis is reviewed, with particular emphasis on those cases where the active sites have been properly identified, and useful activity correlations established.
547 citations
TL;DR: In this paper, the textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N 2 adsorption-desorption, XRD, UV-vis DRS, TPR, SEM-EDS and TPH.
Abstract: Nickel catalysts supported on binary CeO 2 –ZrO 2 carriers (28–100% CeO 2 molar content) were prepared and evaluated regarding their catalytic performance for the CO 2 reforming of CH 4 (Dry Reforming of Methane, DRM). The textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N 2 adsorption–desorption, XRD, UV–vis DRS, TPR, SEM–EDS and TPH. Zirconium improves the textural properties of the CeO 2 –ZrO 2 supports and the corresponding catalysts and enhances their textural stability under thermal reductive treatment. XRD analysis shows the formation of Ce x Zr 1− x O 2 solid solution for all Ce/(Ce + Zr) ratios. Considerable alterations in the electronic environment of the cations and increased lattice defects in the binary solid solutions were detected by UV–vis DR spectroscopy. A significant increase in the reducibility of both supports and catalysts is observed in the presence of Zr. Compared to the zirconia-free sample, the Ni/CeO 2 -ZrO 2 catalysts exhibited much higher activity for the title reaction, accredited to the increase of the surface concentration of the active sites. However, the amount of carbonaceous deposits is not straightforward related to the activity but depends on the Ce/Zr ratio. Among the zirconium containing catalysts, the zirconium-rich one exhibited the higher activity and the stronger resistance to the formation of carbonaceous deposits.
366 citations
TL;DR: In this paper, the effect of using a nanofibrous Al 2 O 3 as support for Ni-based catalysts, modified with Pt, for the dry reforming of methane (DRM) was studied.
268 citations
TL;DR: In this article, the effect of metal doping on surface morphology, electronic interaction, and catalytic efficiency of Co-B-based ternary alloy catalysts for H2 generation by hydrolysis of NaBH4 was investigated.
251 citations
TL;DR: Tungsten carbide nanoparticles were supported on a new 3D mesoporous carbon replicated from commercial silica and exhibited selectivity as high as 72.9% for the catalytic conversion of cellulose into ethylene glycol.
249 citations
TL;DR: In this article, a novel iron titanate catalyst prepared by conventional co-precipitation method showed excellent activity, N-2 selectivity and H2O/SO2 durability in the selective catalytic reduction (SCR) of NO with NH3.
Abstract: A novel iron titanate catalyst prepared by conventional co-precipitation method showed excellent activity, N-2 selectivity and H2O/SO2 durability in the selective catalytic reduction (SCR) of NO with NH3. The influence of precursors and preparation methods on the catalyst structure and activity was comprehensively investigated. Iron titanate catalyst prepared using titanium sulfate as Ti precursor was favorable for the high activity and selectivity, comparing with that using titanium tetrachloride as precursor and Fe2O3/TiO2 loaded type catalyst. Especially, the best iron titanate catalyst showed good activity in a temperature window of 200-350 degrees C with the NOx conversion above 90% in the absence of H2O, which was 50-150 degrees C lower than those of other known Fe-based catalysts. Iron titanate crystallite with specific Fe-O-Ti structure was found to be the main active phase. The interaction between iron and titanium species in atomic scale led to an enhancement of oxidative ability of Fe3+, which was beneficial to the SCR reaction. (C) 2010 Elsevier B.V. All rights reserved.
241 citations
TL;DR: The present Review focuses on the catalytic performance of noble metal- and non precious metal-based embedded catalysts with respect to traditional impregnated systems, and emphasis is dedicated to the improved thermal stability of these nanostructures compared to conventional systems.
Abstract: Industrial catalysts are typically made of nanosized metal particles, carried by a solid support. The extremely small size of the particles maximizes the surface area exposed to the reactant, leading to higher reactivity. Moreover, the higher the number of metal atoms in contact with the support, the better the catalyst performance. In addition, peculiar properties have been observed for some metal/metal oxide particles of critical sizes. However, thermal stability of these nanostructures is limited by their size; smaller the particle size, the lower the thermal stability. The ability to fabricate and control the structure of nanoparticles allows to influence the resulting properties and, ultimately, to design stable catalysts with the desired characteristics. Tuning particle sizes provides the possibility to modulate the catalytic activity. Unique and unexpected properties have been observed by confining/embedding metal nanoparticles in inorganic channels or cavities, which indeed offers new opportunities for the design of advanced catalytic sytems. Innovation in catalyst design is a powerful tool in realizing the goals of more green, efficient and sustainable industrial processes. The present Review focuses on the catalytic performance of noble metal- and non precious metal-based embedded catalysts with respect to traditional impregnated systems. Emphasis is dedicated to the improved thermal stability of these nanostructures compared to conventional systems.
TL;DR: In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed and general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions.
Abstract: In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL) film is immobilized on a high-surface area porous solid and a homogeneous catalyst is dissolved in this supported IL layer, thereby combining the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed. In the first part, general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions. Secondly, organic reactions in which SILP technology is applied to improve the performance of homogeneous transition-metal catalysts are presented: hydroformylation, metathesis reactions, carbonylation, hydrogenation, hydroamination, coupling reactions and asymmetric reactions.
TL;DR: In this paper, the advantages of using CNTs to promote catalyst performance and stability, and a perspective on research directions and strategies to improve fuel cell performance and durability are discussed.
Abstract: Catalyst support materials exhibit great influence on the performance and durability of proton exchange membrane (PEM) fuel cells. This minireview article summarises recent developments into carbon nanotube-based support materials for PEM fuel cells, including the membrane electrode assembly (MEA). The advantages of using CNTs to promote catalyst performance and stability, a perspective on research directions and strategies to improve fuel cell performance and durability are discussed. It is hoped that this minireview will act as a conduit for future developments in catalyst supports and MEA design for PEM fuel cells.
TL;DR: The preparation of Au-Pd nanocrystalline catalysts supported on activated carbon prepared via a sol-immobilization technique is reported and their use for the direct synthesis of hydrogen peroxide and the oxidation of benzyl alcohol is explored.
Abstract: We report the preparation of Au-Pd nanocrystalline catalysts supported on activated carbon prepared via a sol-immobilization technique and explore their use for the direct synthesis of hydrogen peroxide and the oxidation of benzyl alcohol. In particular, we examine the synthesis of a systematic set of Au-Pd colloidal nanoparticles having a range of Au/Pd ratios. The catalysts have been structurally characterized using a combination of UV-visible spectroscopy, transmission electron microscopy, STEM HAADF/XEDS, and X-ray photoelectron spectroscopy. The Au-Pd nanoparticles are found in the majority of cases to be homogeneous alloys, although some variation is observed in the AuPd composition at high Pd/Au ratios. The optimum performance for the synthesis of hydrogen peroxide is observed for a catalyst having a Au/Pd 1:2 molar ratio. However, the competing hydrogenation reaction of hydrogen peroxide increases with increasing Pd content, although Pd alone is less effective than when Au is also present. Investigation of the oxidation of benzyl alcohol using these materials also shows that the optimum selective oxidation to the aldehyde occurs for the Au/Pd 1:2 molar ratio catalyst. These measured activity trends are discussed in terms of the structure and composition of the supported Au-Pd nanoparticles.
TL;DR: In this article, the authors reported the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) using a Chemical Vapor Deposition (CVD) process at temperature ranging from 600°C to 850°C and ethane/ammonia concentration (defined as a volume percentage of C 2 H 6 /(C 2H 6 ǫ+NH 3 )) of 20-100% Several characterizations, i.e., XPS, SEM and TEM were done on the as-synthesized nitrogen-drained carbon nan
Abstract: This work reports the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) using a Chemical Vapor Deposition (CVD) process at temperature ranging from 600 °C to 850 °C and ethane/ammonia concentration (defined as a volume percentage of C 2 H 6 /(C 2 H 6 + NH 3 )) of 20–100% Several characterizations, ie XPS, SEM and TEM were done on the as-synthesized nitrogen-doped carbon nanotubes in order to get more insight about the influence of the synthesis conditions on the characteristics and properties of these N-CNTs Depending on the synthesis conditions, the atomic percentage of nitrogen in carbon nanotubes varied from 0 at% to about 55 at% The undoped carbon nanotubes (N-free CNTs) and two kinds of N-CNTs with different types of nitrogen incorporated species have been used as the supports for palladium in the liquid-phase hydrogenation of cinnamaldehyde The introduction of nitrogen atoms into the carbon matrix significantly modified the chemical properties of the support compared to the N-free carbon nanotube resulting in a higher metal dispersion N-CNTs exhibit much higher activity in the hydrogenation reaction compare to the undoped ones Nitrogen incorporation also strongly improved the selectivity towards the C C bond hydrogenation The results show that the type of nitrogen species incorporated in CNTs structure can also influence the catalytic activity Recycling test confirms the high stability of the catalyst as neither palladium leaching nor deactivation has been observed
TL;DR: In this article, the nano-composite films of expandable graphene sheet (Pt/EGS) are fabricated on conductive indium tin oxide glass electrodes via a green electrochemical synthetic route involving a series of electrochemical processes.
TL;DR: In this paper, two bimetallic PtNi catalysts supported on a nanostructured γ-Al2O3 together with corresponding monometallic materials, employed for the dry reforming of methane, have been prepared and characterized.
TL;DR: In this paper, a facile process to decorate graphene sheets with well-dispersed Pd nanoparticles was reported, and a Pd/TEG composite was prepared and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer−Emmett−Teller (BET) surface area analysis.
Abstract: As a two-dimensional carbon nanomaterial, graphene has a high surface area and good chemical stability; therefore, its potential applicability in composite materials and as a catalyst support is high. Here, we report a facile process to decorate graphene sheets with well-dispersed Pd nanoparticles. By the in situ formation and adhesion of Pd nanoparticles to the thermally exfoliated graphene (TEG) sheets suspended in a solvent, a Pd/TEG composite was prepared and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer−Emmett−Teller (BET) surface area analysis. The migration and aggregation of Pd nanoparticles on the graphene sheets was directly observed by scanning transmission electron microscopy. As the composite was heated to 700 °C, there was little movement of the Pd nanoparticles; on heating to 800 °C, well below the melting temperature, the Pd nanoparticles began to migrate, coalesce, and agglomerate to form larger particles. The aggregation behavior was fu...
TL;DR: In this paper, the bimetallic catalyst was used for carbon dioxide reforming of methane using a quartz tube microreactor at a CH4/CO2 feed ratio of 1, 750 ÂC, 1 Â atm with a gas hourly space velocity of 125,000 ÂmL/g/h.
Abstract: MgO–ZrO2 mesoporous support (Zr/Mg molar ratio = 9) impregnated with 6 wt% Ni, 6 wt% Co and 3 wt% of both Ni and Co were prepared using a novel surfactant assisted-impregnation method. Carbon dioxide reforming of methane using these catalysts was studied in a quartz tube microreactor at a CH4/CO2 feed ratio of 1, 750 °C, 1 atm with a gas hourly space velocity of 125,000 mL/g/h. Based on reactant's conversion and syngas production, the bimetallic catalyst was the most suitable catalyst for the reaction. The catalyst exhibited high and constant activity during 40 h reaction time with methane and carbon dioxide conversions of 80% and 84%, respectively with a syngas ratio close to unity without significant deactivation as compared to the respective monometallic catalysts. For longer time on stream, the catalyst showed constant activity up to 60 h after which it gradually decreased. The bimetallic catalyst also exhibited excellent regenerability by restoring its initial catalytic activity after 1 h of regeneration in air. The catalysts were also characterized by XRD, XPS, N2-physisorption, H2-chemisorption, TGA-DTA, HRTEM, H2-TPR, TPH and SEM. The high performance of the bimetallic catalyst was due to the stabilization of t-phase in zirconia, better metal dispersion, small metal particle size and synergetic effect between Ni and Co particles. The XPS results showed that bimetallic catalyst had the ability to hinder metal oxidation and exhibited presence of higher surface basicity which were responsible to maintain the stability of the catalyst.
TL;DR: In this article, the catalytic performance of glycerol steam reforming over Ni catalysts supported on bare CeO 2 and Al 2 O 3, and with the addition of low ceria loadings enhances the activity of the NiAl catalyst.
TL;DR: Graphene nanosheet was prepared by modified Hummer's chemical method and utilized as a catalyst support of PtRu nanoparticles for the electro-oxidation of methanol as mentioned in this paper.
TL;DR: In this paper, the authors investigated the performance of a Pt catalyst supported on a novel Mg(Ga)(Al)O mixed oxide support for the dehydrogenation of both ethane and propane.
TL;DR: In this paper, the authors classified the solid catalysts into two categories based on their catalytic temperature, i.e. high temperature catalysts and low temperature catalyst, and provided a review of three aspects, catalyst activity, catalyst life and oil flexibility.
Abstract: Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel and have been studied intensively over the last decade. Unlike the homogeneous catalysts, heterogeneous catalysts can be easily separated from reaction mixture and reused for many times. They are environmentally benign and could be easily operated in continuous processes. This review classifies the solid catalysts into two categories based on their catalytic temperature, i.e. high temperature catalysts and low temperature catalysts. The nature of the catalysts can be specified into solid bases and solid acids. Three aspects, catalyst activity, catalyst life and oil flexibility, will be reviewed. Two kinds of heterogeneous catalysts, reported by IFP Inc. and by WSU, respectively, show a high catalytic activity, long catalyst life and low leaching of catalyst components. These two catalysts also show ability to simultaneously catalyze esterification and transesterification, and can be used in half-refined or crude oil system which provide a potential for greatly decrease the feedstock cost.
TL;DR: In this article, a one-pot method to synthesize hierarchically ordered porous carbons with interconnected macropores and mespores via in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source is presented.
Abstract: This article presents a one-pot method to synthesize hierarchically ordered porous carbons with interconnected macropores and mespores, via in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source. Compared with other techniques, this procedure is veritably simple; neither presynthesis of the macropore/mesopore or crystal templates nor additional infiltration is needed, and the self-assembly of polymer spheres into the crystal template and the infiltration are finished in situ in the same system. The sizes of macropores and mesopores can be independently tuned by the sizes of polymer and silica spheres, respectively. The obtained bimodal porous carbons have large BET surface areas, large pore volumes, and partially graphitized frameworks. They show very good support of the Pt−Ru alloy catalyst in a direct methanol fuel cell.
TL;DR: In this article, a ruthenium supported on graphite catalyst (Ru/G) for hydrogen generation from sodium borohydride (NaBH(4)) solution is prepared by a modified impregnation method.
TL;DR: In this paper, the Pt/NbxTi(1−−−x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring disk electrode (RRDE).
Abstract: Rutile phase niobium-doped titanium oxide [NbxTi(1 − x)O2, x = 0.25] with a high electrical conductivity (1.11 S cm−1) was synthesized and investigated as a cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The TEM image of the Pt/NbxTi(1 − x)O2 catalyst revealed that Pt particles (dPt = 3–4 nm) were deposited on the NbxTi(1 − x)O2 support using a borohydride reduction method. The Pt/NbxTi(1 − x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring-disk electrode (RRDE). The results of an accelerated durability test (ADT, continuous cycling between 0.6 and 1.4 V) in RRDE indicated high stability for the Pt/NbxTi(1 − x)O2 electrocatalysts at high potentials in terms of minimum loss in Pt electrochemical surface area (ECSA). Furthermore, the Pt/NbxTi(1 − x)O2 showed nearly 10-fold higher ORR activity after potential cycling tests when compared to the Pt/C catalyst (1.19 and 0.13 mA cm−2 for Pt/NbxTi(1 − x)O2 and Pt/C, respectively). The Pt/C catalyst showed no activity in fuel cell testing after 1000 cycles due to severe carbon corrosion and subsequent disintegration of the catalyst layer. Conversely, the Pt/NbxTi(1 − x)O2 catalyst showed only a small voltage loss (0.11 V at 0.6 A cm−2) even after 3000 cycles. Based on the ADT results, the Pt/NbxTi(1 − x)O2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.
TL;DR: In this article, the production of hydrogen from ethanol steam reforming with Cu-Ni catalysts supported on MgO-and CaO-modified silica has been studied and two promoting effects have been found: reduction of the metallic CuNi particles size and strengthening of the metal-support interaction.
TL;DR: In this article, Pt catalysts prepared on different supports were evaluated in order to apply them in the steam reforming of glycerol reaction to obtain hydrogen and/or synthesis gas at temperatures lower than 450°C.
TL;DR: The role of the catalyst and the catalyst support is discussed, and the recent results obtained from the water assisted growth and the equimolar C2H2-CO2 reaction are discussed.
Abstract: The catalytic chemical vapor deposition (CCVD) is currently the most flexible and economically attractive method for the growth of carbon nanotubes. Although its principle is simple, the precisely controlled growth of carbon nanotubes remains very complex because many different parameters influence the growth process. In this article, we review our recent results obtained on the synthesis of carbon nanotubes via CCVD. We discuss the role of the catalyst and the catalyst support. Our recent results obtained from the water assisted growth and the equimolar C2H2-CO2 reaction are also discussed. Both procedures lead to significantly enhanced carbon nanotube growth. In particular, the latter allows growing carbon nanotubes on diverse substrate materials at low temperatures.
TL;DR: SiO2-supported Pt/WO3/TiO2 catalysts were prepared; they were found to be more active and selective than the Pt/ WO3, TiO2, and SiO2 catalyst for glycerol hydrogenolysis to 1,3-propanediol in a slurry batch reactor.
Abstract: SiO2-supported Pt/WO3/TiO2 catalysts were prepared; they were found to be more active and selective than the Pt/WO3/TiO2 catalyst for glycerol hydrogenolysis to 1,3-propanediol in a slurry batch reactor. The influences of catalyst component, reaction medium, reaction temperature, H2 pressure and reaction time on glycerol hydrogenolysis over the Pt/WO3/TiO2/SiO2 catalyst were investigated. XRD, TEM, NH3-TPD and Py-IR characterization were employed to reveal the roles of WO3 and TiO2 in the performance of the Pt based-catalysts. XRD patterns and TEM images showed that the presence of TiO2 species in the catalyst favored the dispersion of platinum. The weak Bronsted acid sites formed by addition of WO3 to the catalyst were concluded to play a key role in selective formation of 1,3-propanediol, based on the results of NH3-TPD and Py-IR characterization.