Showing papers on "Catalyst support published in 2011"
TL;DR: The data indicate that better control of the metal-catalyzed transformations of the polymer into new graphitized carbon forms in the heat-treatment step will allow for even further improvement of this class of catalysts.
Abstract: In this report, we present the systematic preparation of active and durable non-precious metal catalysts (NPMCs) for the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs) based on the heat treatment of polyaniline/metal/carbon precursors. Variation of the synthesis steps, heat-treatment temperature, metal loading, and the metal type in the synthesis leads to markedly different catalyst activity, speciation, and morphology. Microscopy studies demonstrate notable differences in the carbon structure as a function of these variables. Balancing the need to increase the catalyst’s degree of graphitization through heat treatment versus the excessive loss of surface area that occurs at higher temperatures is a key to preparing an active catalyst. XPS and XAFS spectra are consistent with the presence of Me–Nx structures in both the Co and Fe versions of the catalyst, which are often proposed to be active sites. The average speciation and coordination environment of nitrogen and metal, however, depends greatly on the choice of Co or Fe. Taken together, the data indicate that better control of the metal-catalyzed transformations of the polymer into new graphitized carbon forms in the heat-treatment step will allow for even further improvement of this class of catalysts.
509 citations
TL;DR: In this paper, a review of the recent advances in the reaction mechanism and kinetics on group 8-10 base metal catalysts is presented, with special attention paid to the roles of metal particles and the deactivation mechanism of the catalyst during the reaction.
376 citations
TL;DR: In this article, a hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN) was designed to efficiently support noble metal (e.g., PtRu) nanoparticles.
Abstract: A hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN), in which the graphene layers are distributed inside the CNT inner cavities, was designed to efficiently support noble metal (e.g., PtRu) nanoparticles. Well-dispersed PtRu nanoparticles with diameters of 2–4 nm were immobilized onto these NCNT-GHN supports by a low-temperature chemical reduction method without any pretreatment. Compared to conventional CNTs and commercial catalysts. a much better catalytic performance was achieved by a synergistic effect of the hierarchical structure (graphene-CNT hybrid) and electronic modulation (N-doping) during the methanol electrooxidation reaction. Improved single-cell performances with long-term stability are also demonstrated using NCNT-GHN as catalyst support.
352 citations
TL;DR: In-situ catalytic upgrading of biomass fast pyrolysis vapors was performed in a fixed bed bench-scale reactor at 500°C, for catalyst screening purposes, showing the most balanced performance having a moderate selectivity towards hydrocarbons, reducing undesirable compounds and producing organic liquid products at acceptable yields.
341 citations
TL;DR: In this paper, a review examines the extent to which carbon materials have been used as catalyst support materials in the fields of energy and environmental chemistry and identifies potential research applications and directions.
265 citations
TL;DR: In this article, the major findings of hydrothermal gasification over the past two decades with the aid of heterogeneous catalysts in terms of activity, hydrogen selectivity and stability are reviewed.
254 citations
TL;DR: A review of the different metal oxides commonly used in the process of transesterification of oils for the production of biodiesel with special reference to the various methods of catalyst preparation and catalyst characterization is provided in this article.
Abstract: Biodiesel production is worthy of continued study and optimization of production procedures due to its environmentally beneficial attributes and its renewable nature. Heterogeneous transesterification is considered to be a green process. The process requires neither catalyst recovery nor aqueous treatment steps and very high yields of methyl esters can be obtained, close to the theoretical value. However, heterogeneously catalyzed transesterification generally requires more severe operating conditions, and the performance of heterogeneous catalysts is generally lower than that of the commonly used homogeneous catalysts. Heterogeneous catalysis for biodiesel production has been extensively investigated in the last few years. Many metal oxides have been studied for the transesterification process of oils; these include alkali earth metal oxides, transition metal oxides, mixed metal oxides and supported metal oxides. The use of solid metal oxides as catalysts in oil transesterification is well established, accordingly, researchers’ attempts are now focused on how to attain the highest catalyst activity. Catalyst activity is a function of its specific surface area, base strength and base site concentration. High specific surface area, strong base strength and high concentration of base sites are characteristics of an active transesterification catalyst. This review provides a brief overview of the different metal oxides frequently used in the process of transesterification of oils for the production of biodiesel with special reference to the various methods of catalyst preparation and catalyst characterization. Reaction conditions and catalyst leaching analysis are also highlighted. Finally, concluding remarks regarding catalyst selection and catalyst preparation steps are provided.
243 citations
TL;DR: Experimental and computational results suggested that active sites on the Pt/Mo(2)C catalysts were located on the perimeter of the Pt particles and that strong interactions between Pt and the Mo( 2)C surface gave rise to raft-like particles.
Abstract: Nanostructured carbides are refractory materials with high surface areas that could be used as alternatives to the oxide materials that are widely used as support materials for heterogeneous cataly...
241 citations
TL;DR: In this paper, a new hybrid material, PdNPs@CNCs, consisting of monodisperse Pd nanoparticles (PdNs) evenly deposited onto colloidal cellulose nanocrystallites, was presented.
226 citations
TL;DR: In this article, a nickel-based catalysts with a nickel content of 12 wt% were prepared with the zirconia-alumina composite as the supports, and the new catalysts showed higher catalytic activity and better stability than Ni/γ-Al 2 O 3.
217 citations
TL;DR: In this article, the authors investigated three types of catalysts: char, char-supported catalysts and ilmenite for the steam reforming of biomass tar derived from the pyrolysis of mallee wood in situ.
TL;DR: A review of the literature indicates that precise determination of microstructure and in situ observation of reactions at the molecular and atomic levels remain essential tasks as mentioned in this paper, and the potential applications of clay-based heterogeneous catalysts have many practical and potential applications in green catalysis.
TL;DR: A palladium-based catalyst supported on amine-functionalized magnetite nanoparticles was successfully prepared by a facile one-pot template-free method combined with a metal adsorption-reduction procedure as discussed by the authors.
TL;DR: In this paper, a focused ion beam/scanning electron microscopy (FIB/SEM) approach was adopted together with electron tomographic studies to visualize the three-dimensional pore structure of a Pt/C catalyst.
Abstract: During the lifetime of a polymer electrolyte fuel cell, the pore structure of the Pt/C catalyst layer may change as a result of carbon corrosion. Three-dimensional visualization of porosity changes is important to understand the origin of fuel cell performance deterioration. A focused ion beam/scanning electron microscopy (FIB/SEM) approach was adopted together with electron tomographic studies to visualize the three-dimensional pore structure of a Pt/C catalyst. In the case of pristine catalyst layers, the pores form an interconnected network. After 1000 start-up/shut-down cycles, severe carbon corrosion leads to a collapse of the support structure. The porosity of the degraded catalyst layer shrinks drastically, resulting in a structure of predominantly isolated pores. These porosity changes hinder the mass transport in the catalyst layer, consequently leading to a substantial loss of fuel cell performance. FIB/SEM serial sectioning and electron tomography allows three-dimensional imaging of the catalys...
TL;DR: In this paper, a sequential deposition-precipitation method was used to synthesize bimetallic catalysts with different Au/Ag atomic ratios for the reaction of CO oxidation.
TL;DR: In this paper, the authors highlight the development of novel supported gold catalysts from a materials perspective, mostly from those reported by their group, are given concerning the developments of simple Gold catalysts with single metal-support interfaces and heterostructured Gold catalyst with complicated interfacial structures, which not only provide possibilities for applied catalysis, but also furnish grounds for fundamental research.
Abstract: Since Haruta et al. discovered that small gold nanoparticles finely dispersed on certain metal oxide supports can exhibit surprisingly high activity in CO oxidation below room temperature, heterogeneous catalysis by supported gold nanoparticles has attracted tremendous attention. The majority of publications deal with the preparation and characterization of conventional gold catalysts (e.g., Au/TiO2), the use of gold catalysts in various catalytic reactions, as well as elucidation of the nature of the active sites and reaction mechanisms. In this overview, we highlight the development of novel supported gold catalysts from a materials perspective. Examples, mostly from those reported by our group, are given concerning the development of simple gold catalysts with single metal-support interfaces and heterostructured gold catalysts with complicated interfacial structures. Catalysts in the first category include active Au/SiO2 and Au/metal phosphate catalysts, and those in the second category include catalysts prepared by pre-modification of supports before loading gold, by post-modification of supported gold catalysts, or by simultaneous dispersion of gold and an inorganic component onto a support. CO oxidation has generally been employed as a probe reaction to screen the activities of these catalysts. These novel gold catalysts not only provide possibilities for applied catalysis, but also furnish grounds for fundamental research.
TL;DR: In this paper, a Pt/TiO 2 electrocatalyst was synthesized and investigated as alternative cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs).
Abstract: Titania supported Pt electrocatalysts (Pt/TiO 2 ) were synthesized and investigated as alternative cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Transmission electron microscope (TEM) images revealed uniform distribution of Pt nanoparticles ( d Pt = 3–5 nm) on the TiO 2 support. The Pt/TiO 2 electrocatalyst showed comparable activity to that of a commercial Pt/C catalyst (TKK) in fuel cell studies. The fuel cell accelerated stress test (AST) for catalysts demonstrated similar stability for Pt/TiO 2 and Pt/C. In-house developed accelerated durability test (ADT, continuous potential cycling between 0.6 and 1.4 V) in half-cell condition indicated nearly ten-fold higher ORR activity (1.20 mA cm −2 ) when compared to the Pt/C catalyst (0.13 mA cm −2 ). The Pt/C catalyst showed no activity in fuel cell testing after 2000 potential cycles due to severe carbon corrosion, Pt dissolution, and catalyst particle sintering. Conversely, the Pt/TiO 2 electrocatalyst showed only a small voltage loss (0.09 V at 0.8 A cm −2 ) even after 4000 cycles. Furthermore, the ADT results showed excellent stability for the Pt/TiO 2 electrocatalysts at high potentials in terms of minimum loss in the Pt electrochemical surface area (ECSA). The high stability of the Pt/TiO 2 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 paper, the authors investigated the performance of Ni/SiO2 catalysts with La, Mg, Co and Zn and found that the addition of La and Mg decreased the contribution of reverse water-gas shift reaction, leading to higher H2 yield.
TL;DR: In this article, the impact of water on the stability of Mo and CoMo sulfide catalysts in hydrodeoxygenation of phenolic compounds was investigated and it was shown that large amounts of water at reaction temperature lead to the exchange of an important fraction of edge sulfur atoms on non-promoted MoS2 catalysts, hence changing the nature of the active sites.
TL;DR: In this paper, a simple method was developed to prepare ultra-low Pt loading membrane electrode assembly (MEA) using vertically aligned carbon nanotubes (VACNTs) as highly ordered catalyst support for PEM fuel cells application.
Abstract: A simple method was developed to prepare ultra-low Pt loading membrane electrode assembly (MEA) using vertically aligned carbon nanotubes (VACNTs) as highly ordered catalyst support for PEM fuel cells application. In the method, VACNTs were directly grown on the cheap household aluminum foil by plasma enhanced chemical vapor deposition (PECVD), using Fe/Co bimetallic catalyst. By depositing a Pt thin layer on VACNTs/Al and subsequent hot pressing, Pt/VACNTs can be 100% transferred from Al foil onto polymer electrolyte membrane for the fabrication of MEA. The whole transfer process does not need any chemical removal and destroy membrane. The PEM fuel cell with the MEA fabricated using this method showed an excellent performance with ultra-low Pt loading down to 35 μg cm−2 which was comparable to that of the commercial Pt catalyst on carbon powder with 400 μg cm−2. To the best of our knowledge, for the first time, we identified that it is possible to substantially reduce the Pt loading one order by application of order-structured electrode based on VACNTs as Pt catalysts support, compared with the traditional random electrode at a comparable performance through experimental and mathematical methods.
TL;DR: In this paper, a series of Mo-and NiMo-catalysts were supported on ZrO2, Al2O3, SBA-15, and Zr O2-modified SBA15 and tested in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzethiophene(4,6)-DMDBT).
TL;DR: In this article, a magnetically-recoverable catalyst was synthesized by the immobilization of H3PW12O40 on the surface of silica-encapsulated γ-Fe2O3 nanoparticles.
TL;DR: In this paper, a review discusses the synthesis and the possible applications of nitrogen-doped carbon nanotubes as supports for metal nanoparticles in heterogeneous catalysis, and discusses the applications of carbon-based supports for noble metal catalysts.
Abstract: The science and technology of catalysis is of fundamental importance to a national economy. Today about 90% of all technical chemicals are manufactured by the use of catalysts. Nanoparticles of noble metals are extremely important materials in the catalysis industry due to cost issues and properties that are not found in their bulk state. An efficient way to produce and stabilise noble metal nanoparticles is by dispersion on a suitable support. Carbon-based supports, such as carbon nanotubes, carbon spheres, carbon fibres, etc., have been found to be good supports for metal nanoparticles. However, to be used effectively, the carbon surface must be modified either by functionalisation or doping. This review discusses the synthesis and the possible applications of nitrogen-doped carbon nanotubes as supports for metal nanoparticles in heterogeneous catalysis.
TL;DR: In this article, it was shown that Pd nanoparticles dispersed on GNS were highly active for the electrooxidation of ethanol and methanol in 1 M KOH.
TL;DR: In this article, a ligand-assisted assembly approach is demonstrated for the synthesis of thermally stable and large-pore ordered mesoporous titanium dioxide with a highly crystalline framework by using diblock copolymer poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template and titanium isopropoxide (TIPO) as precursor.
Abstract: A novel ligand-assisted assembly approach is demonstrated for the synthesis of thermally stable and large-pore ordered mesoporous titanium dioxide with a highly crystalline framework by using diblock copolymer poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template and titanium isopropoxide (TIPO) as a precursor. Small-angle X-ray scattering, X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution scanning electron microscopy, and N2-sorption measurements indicate that the obtained TiO2 materials possess an ordered primary cubic mesostructure with large, uniform pore diameters of about 16.0 nm, and high Brunauer–Emmett–Teller surface areas of ∼112 m2 g−1, as well as high thermal stability (∼700 °C). High resolution TEM and wide-angle XRD measurements clearly illustrate the high crystallinity of the mesoporous titania with an anatase structure in the pore walls. It is worth mentioning that, in this process, in addition to tetrahydrofuran as a solvent, acetylacetone was employed as a coordination agent to avoid rapid hydrolysis of the titanium precursor. Additionally, stepped evaporation and heating processes were adopted to control the condensation rate and facilitate the assembly of the ordered mesostructure, and ensure the formation of fully polycrystalline anatase titania frameworks without collapse of the mesostructure. By employing the obtained mesoporous and crystallized TiO2 as the photoanode in a dye-sensitized solar cell, a high power-conversion efficiency (5.45%) can be achieved in combination with the N719 dye, which shows that this mesoprous titania is a great potential candidate as a catalyst support for photonic-conversion applications.
TL;DR: In this paper, the authors examined the generation of hot-spots and their impact in the heterogeneous Suzuki-Miyaura coupling reaction for the synthesis of 4-methylbiphenyl in toluene solvent in the presence of Pd/AC.
Abstract: This article examines the generation of hot-spots and their impact in the heterogeneous Suzuki–Miyaura coupling reaction for the synthesis of 4-methylbiphenyl in toluene solvent in the presence of Pd/AC. Hot-spots easily formed on the surface of the activated carbon (AC) catalyst support under high electric field conditions; they were recorded in real time using a high-speed camera. Chemical yields of 4-methylbiphenyl under the microwaves’ magnetic field (H-field) were 2-fold greater than those under electric field (E-field) conditions at identical temperatures and reaction times (120 min). Microwave E-field irradiation with a high accuracy device enhanced generation of hot-spots. Excessive formation of hot-spots impacted negatively on this coupling reaction.
TL;DR: In this paper, a molybdenum carbide catalyst with a novel methodology and its toluene hydrogenation activity tested at temperatures within 423-598 K and 2.76 MPa was reported.
Abstract: A molybdenum carbide catalyst prepared with a novel methodology and its toluene hydrogenation activity tested at temperatures within 423–598 K and 2.76 MPa is here reported. Almost 100% hydrogenation was achieved at 473 K with this catalyst. The activation energy was 58.1 kJ/mol with a zero-order reaction for toluene concentration, illustrating a behavior comparable to that of noble metals. Additional catalyst formulations were tested and their activities compared between them. XRD and Raman characterization of the catalysts allowed identification of several species in the newly synthesized catalyst, namely fcc-Mo 2 C and MoO 2 .
TL;DR: In this paper, the Fischer-Tropsch synthesis was evaluated on cobalt-based catalyst supported on a medium surface area SiC foam ceramic in a fixed-bed configuration, and the results indicated that under severe FTS reaction conditions the SiC seems to be more suitable support than alumina.
Abstract: The Fischer–Tropsch synthesis was evaluated on cobalt based catalyst supported on a medium surface area SiC foam ceramic in a fixed-bed configuration. The catalytic results were compared with those obtained on a Co/Al2O3 foam catalyst. At medium conversion (<50%) the two catalysts display similar C5+ selectivity indicate that the intrinsic selectivity between the two catalysts is close from each other. However, when the CO conversion was increased to 70%, a significant difference in terms of the C5+ selectivity was observed between the two catalysts, i.e. 80% on the Co/SiC and 54% on the Co/Al2O3, which indicate that under severe FTS reaction conditions the SiC seems to be more suitable support than alumina. It is also worth to note that under these reaction conditions the chain length probability, α, obtained on the SiC-based catalyst was 0.91 and wax formation was especially favoured. The improvement of the C5+ selectivity observed on the SiC catalyst was attributed to the high efficiency of the support to evacuate heat generated during the course of the reaction owing to it higher thermal conductivity and also to the presence of meso- and macro-porosity of the support. Additional catalytic test conducted on a hybrid support, i.e. Al2O3 coated SiC foam, again confirms the high C5+ selectivity under a similar severe reaction conditions in the presence of a SiC structure underneath of the alumina layer which play a role of heat disperser. In addition, the high chemical inertness of the SiC material also allows one to perform an easy recovery of both the active phase and the support by a simple acid washing. The recovered SiC support was further impregnated with a fresh cobalt phase and re-tested in the FTS and the catalytic results are compared with those of the former catalyst. The same product yield was obtained which confirms the potential of SiC to be employed as a re-usable support.
TL;DR: In this article, a general method was developed for the synthesis of Fe3O4@polymer microspheres with well-defined core-shell structure and various functional groups and strong magnetization through a facile in situ distillation-precipitation polymerization.
Abstract: A general method was developed for the synthesis of Fe3O4@polymer microspheres with well-defined core–shell structure and various functional groups and strong magnetization through a facile in situ distillation–precipitation polymerization. In this approach, the as-prepared Fe3O4 microspheres were directly coated by a polymer shell through the hydrogen bond interaction between the Fe3O4 micropsheres and oligomer without any surface modification. Moreover, hydrophilic or hydrophobic monomer or even their comonomers with different functional groups such as carboxyl, hydroxyl, amide, and ester were facilely encapsulated onto the surface of the magnetite microspheres. The thickness of the polymer shell layer was tuned by the feed of monomer amount. As for application, Fe3O4@P(MBAAm-co-MAA) microspheres that contained carboxyl groups were used as a magnetic catalyst support to load a series of metallic nanoparticles such as Ag, Pt, and Au. These strong magnetic microspheres were characterized by transmission e...
Book•
26 Jul 2011
TL;DR: In this article, the first synthetic catalysts were described. And the first chemical catalysts for industrial use were shown to be hydrogenation and Oxidation Catalysts, as well as catalytic cracking catalysts.
Abstract: Industrial Catalysts.- The First Catalysts.- Hydrogenation Catalysts.- Oxidation Catalysts.- Catalytic Cracking Catalysts.- Refinery Catalysts.- Petrochemical Catalysts.- Olefin Polymerization Catalysts.- Synthesis Gas.- Ammonia and Methanol Synthesis.- Environmental Catalysts.- Index.