Showing papers on "Catalyst support published in 2015"

Multiple roles of graphene in heterogeneous catalysis

Abstract: Scientific interest in graphene as a catalyst and as a catalyst support in heterogeneous catalytic reactions has grown dramatically over the past several years. The present critical review summarizes the multiple roles of graphene in heterogeneous catalysis and highlights the influence of defects, heteroatom-containing functionalities, and graphene's two-dimensional structure on catalytic performance. We first discuss the role and advantages of graphene as a catalyst support, with emphasis on its interactions with the catalytic phases and the influence of mass transfer processes. We then clarify the origin of the intrinsic catalytic activity of graphene in heterogeneous catalytic reactions. Finally we suggest challenges and potential practical applications for graphene in industrial processes.

H2S-Selective Catalytic Oxidation: Catalysts and Processes

Abstract: The most widely used catalysts and processes for H2S-selective catalytic oxidation are overviewed in this review. Two kinds of catalysts have been investigated intensively: carbon-based catalysts (active carbon catalyst, carbon nanotube catalyst, and carbon nanofiber catalyst), metal oxide-based catalysts (metal oxide catalyst, oxide-supported catalyst, and clay-supported catalyst). Among them, carbon-based catalysts are utilized mainly in discontinuous processes at relatively low temperatures, whereas metal oxide catalysts are the most widely used in practice. However, the reaction temperature is relatively high. Fortunately, a MgAlVO catalyst derived from LDH materials and intercalated clay-supported catalysts exhibit excellent catalytic activities at relatively lower temperatures. According to various studies, the catalytic behaviors mainly obey the Mars–van Krevelen mechanism; however, the catalyst deactivation mechanism differs, depending on the catalyst. In practice, the mobil direct oxidation proce...

A Review on the Pd-Based Three-Way Catalyst

Abstract: The application of Pd in three-way catalyst represents a significant technology breakthrough for the removal of pollutants from gasoline powered vehicle exhaust gas. Pd shows superior catalytic activity for hydrocarbon (HCs) oxidation and thermal stability to the conventional Pt/Rh catalyst. However, Pd catalysts are more susceptible to chemical poisoning. This work summarizes the progress of the Pd-based three-way catalyst and its related technologies. The state of Pd in the reaction, the support and oxygen storage material, the promoters, and preparation methods on the catalytic performance are reviewed. The process and catalyst configurations, e.g., close-couple (CCC), dual bricks, layered, and zone-coated catalysts, are described and compared. The advances in the understanding of the reaction and deactivation mechanisms in the three-way catalysis systems are also discussed.

Coke-resistant Ni@SiO2 catalyst for dry reforming of methane

Abstract: Nanostructured Ni@SiO2 core–shell catalyst is prepared from nickel oxide nanoparticles by a facile method. Calcination of as-synthesized core–shell nanoparticles creates a micro/meso-porous structure in the amorphous silica shell. The catalytic performance of core–shell catalyst toward dry reforming of methane was first evaluated in a thermogravimeter coupled with a mass spectrometer. Coking is negligible in a reforming period of 40 h on stream at 850 °C, while more than 0.32 gcoke gcat−1 is produced on a commercial Ni-based reforming catalyst in 6.4 h at the same reforming condition. Dry reforming was also performed in a continuous flow, fixed-bed reactor at 750 °C. Characterization of spent catalyst further confirms that Ni@SiO2 catalyst has high coke-resistance for dry reforming. The amount of coke deposited on the core–shell catalyst in 24.5 h is 0.012 gcoke gcat−1.

Review on the photocatalytic activity of various composite catalysts

Abstract: Nano sized semiconductor photocatalysts have a great scope for removal of large organic molecules like dyes and pesticides in an eco-friendly and sustainable manner. The photocatalytic decomposition of dyeing industrial wastewater produces negligible amount of solid by products. The problem associated with the existing catalysts are, their high band gap. Doping one catalyst with other suitable metals and metal oxides will enhance the efficiency of the photocatalyst and also makes the catalyst to be active in the visible region. The photocatalytic activity of the composite catalysts were highly improved through the modification in the crystallinity, micro structures, band gap, morphology, particle size and the surface area of the catalyst. This paper reviews the recent developments in the synthesis and application of composite photocatalysts. The role of synthetic pathways on the structure and activity of composite catalyst derived from TiO2, CdS, WO3, SnS and ZnO were analyzed. This paper will be more helpful for the scientists working in the field of nano sized photocatalysis.

A general post-synthetic modification approach of amino-tagged metal–organic frameworks to access efficient catalysts for the Knoevenagel condensation reaction

Abstract: In this manuscript, four common transition-metal derived metal–organic frameworks have been extensively investigated as heterogeneous catalyst supports for Knoevenagel condensation reactions. A simple post-synthetic modification strategy was employed for the rapid and facile introduction of a primary alkyl amino group. The resulting novel MOF–RNH2 catalysts showed greatly enhanced Knoevenagel condensation reactivities towards a variety of aldehyde electrophiles. IRMOF-3 proved to be an unsuitable heterogeneous catalyst support due to its fragile nature upon treatment with bases. The novel zirconium based UiO-66–NH–RNH2 and chromium based Cr-MIL-101–NH–RNH2 materials showed excellent catalytic reactivities, while being highly convenient to synthesize. The basic catalytic activity was further extended to the Henry reaction, and excellent catalytic reactivity was achieved. The size-selectivity was also studied to show that the Knoevenagel condensation occurred inside of the porous structure of the MOF catalyst. The recycling properties of zirconium, aluminum and chromium derived MOFs were evaluated and zirconium based UiO-66 and chromium based Cr-MIL-101 showed excellent catalytic efficiency after five reaction cycles.

Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions

Abstract: Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e− transfer and superb mechanical properties. Here, the recent progress of NCNTs- and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies.

Rational design and in situ fabrication of MnO2@NiCo2O4 nanowire arrays on Ni foam as high-performance monolith de-NOx catalysts

Abstract: In this work, we have rationally designed and originally developed a novel monolith de-NOx catalyst with nickel foam as the carrier and three dimensional hierarchical MnO2@NiCo2O4 core–shell nanowire arrays in situ grown on the surface via a two-step hydrothermal process with a post calcination treatment. The catalysts were systematically examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, elemental mapping, ion sputtering thinning, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, H2 temperature-programmed reduction, NH3/NO + O2 temperature-programmed desorption measurements and catalytic performance tests. The results indicate that the nanowire is composed of hollow NiCo2O4 spinel as the core and MnO2 nanoparticles as the shell layer. By ingeniously making the hierarchical Ni–Co oxide nanowires as the support for manganese oxides, the MnO2@NiCo2O4@Ni foam catalyst not only takes advantage of the high surface area of Ni–Co nanowires to achieve high loading amounts as well as high dispersion of manganese oxides, but also makes use of the synergistic catalytic effect between Ni, Co and Mn multiple oxides, and exhibits excellent low-temperature catalytic performance in the end. In addition, with the structure and morphology well maintained under long term steady isothermal operation, the catalyst is able to sustain high NO conversion and exhibits superior catalytic cycle stability and good H2O resistance. Considering all these favorable properties, the MnO2@NiCo2O4@Ni foam catalyst could serve as a promising candidate for the monolith de-NOx catalyst at low temperatures and the rational design of in situ synthesis of 3D hierarchical monolith catalysts also puts forward a new way for the development of environmental-friendly and highly active monolith de-NOx catalysts.

Synthesis of Ni and Ni–Cu supported on carbon nanotubes for hydrogen and carbon production by catalytic decomposition of methane

Abstract: Nickel and nickel–copper alloy supported on carbon nanotubes (CNTs) were examined as catalysts for hydrogen production by methane decomposition. The Ni/CNT and Ni–Cu/CNT catalysts were characterized using field emission scanning electron microscopy, energy dispersive X-ray microscopy, transmission electron microscopy and X-ray diffraction. The performance of the catalysts was dependent on the catalyst composition and reaction temperature. The Ni78Cu22/CNT catalyst exhibited the excellent catalytic performance with a stable methane conversion of 0.8 at 700 °C, a carbon yield rate of 0.08 g C/(min g Ni) at 743 °C and a carbon yield of 602 g C/g Ni at 700 °C. Carbon materials with various morphologies, i.e., herringbone carbon nanofibers (CNFs), platelet CNFs, bamboo-shaped CNFs, branched CNFs, multi-branched CNFs and onion-like carbons, depending on the catalyst composition and reaction temperature, were obtained. The morphology of the produced carbon material was correlated with the growth mechanism of the carbon material on the catalyst.

Materials and characterization techniques for high-temperature polymer electrolyte membrane fuel cells

Abstract: The performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) is critically dependent on the selection of materials and optimization of individual components. A conventional high-temperature membrane electrode assembly (HT-MEA) primarily consists of a polybenzimidazole (PBI)-type membrane containing phosphoric acid and two gas diffusion electrodes (GDE), the anode and the cathode, attached to the two surfaces of the membrane. This review article provides a survey on the materials implemented in state-of-the-art HT-MEAs. These materials must meet extremely demanding requirements because of the severe operating conditions of HT-PEMFCs. They need to be electrochemically and thermally stable in highly acidic environment. The polymer membranes should exhibit high proton conductivity in low-hydration and even anhydrous states. Of special concern for phosphoric-acid-doped PBI-type membranes is the acid loss and management during operation. The slow oxygen reduction reaction in HT-PEMFCs remains a challenge. Phosphoric acid tends to adsorb onto the surface of the platinum catalyst and therefore hampers the reaction kinetics. Additionally, the binder material plays a key role in regulating the hydrophobicity and hydrophilicity of the catalyst layer. Subsequently, the binder controls the electrode-membrane interface that establishes the triple phase boundary between proton conductive electrolyte, electron conductive catalyst, and reactant gases. Moreover, the elevated operating temperatures promote carbon corrosion and therefore degrade the integrity of the catalyst support. These are only some examples how materials properties affect the stability and performance of HT-PEMFCs. For this reason, materials characterization techniques for HT-PEMFCs, either in situ or ex situ, are highly beneficial. Significant progress has recently been made in this field, which enables us to gain a better understanding of underlying processes occurring during fuel cell operation. Various novel tools for characterizing and diagnosing HT-PEMFCs and key components are presented in this review, including FTIR and Raman spectroscopy, confocal Raman microscopy, synchrotron X-ray imaging, X-ray microtomography, and atomic force microscopy.

Multifunctionality of Cu–ZnO–ZrO2/H-ZSM5 catalysts for the one-step CO2-to-DME hydrogenation reaction

Abstract: A series of Cu–ZnO–ZrO 2 /H-ZSM5 multifunctional catalysts for the one-step CO 2 -to-DME hydrogenation reaction was prepared via coprecipitation of methanol catalyst precursors by means of different precipitating agents ( i.e. , sodium bicarbonate, ammonium carbonate, oxalic acid and urea) in a slurry containing dispersed zeolite particles. The samples were characterized by XRF, XRD, N 2 adsorption/desorption isotherms, SEM, N 2 O-titration, TPR and NH 3 /CO 2 TPD techniques, while the catalytic testing was carried out in a fixed-bed reactor operating at 3.0 MPa, in the T R range 473–513 K and space velocity of 10,000 h −1 (CO 2 /H 2 /N 2 , 3/9/1). The experiments revealed that the preparation methodology significantly affects catalyst properties and hence catalyst activity. The multifunctional catalyst prepared via ammonium carbonate precipitation resulted to be the most active in CO 2 conversion, also accomplishing high DME selectivity, with a maximum space-time yield of 0.225 kg DME /kg cat /h. Catalyst characterization disclosed that the strength of basic sites, the ratio between acid and basic sites along with the Cu particle sizes are crucial to achieve maximum catalytic performance, keeping CO selectivity to a minimum value.

Multifunctional Au-Fe3O4@MOF core–shell nanocomposite catalysts with controllable reactivity and magnetic recyclability

Abstract: The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications.

A trimetallic V–Co–Fe oxide nanoparticle as an efficient and stable electrocatalyst for oxygen evolution reaction

Abstract: Hydrogen (H2) generated from water splitting is deemed as the ideal replacement for conventional sources of energy. Catalysts play a valuable role in water splitting, especially the oxygen evolution reaction (OER). Here, we report a Fe-doped Co3V2O8 nanoparticle catalyst (iron-rich V–Co–Fe), which possesses outstanding OER catalytic activity with ηj = 10 mA cm−2 = 307 mV, and a low Tafel slope of 36 mV dec−1, benefiting from a large degree of amorphization, a rich porous structure and a high specific surface area (about 232.1 m2 g−1). More remarkably, the catalytic performance of the V–Co–Fe catalyst is markedly superior to commercial ruthenium oxide. In addition, the durability of the V–Co–Fe catalyst is fine. The current density collapses by less than 3 percent at 1.55 V vs. RHE after 11 h in comparison to the initial value. Moreover, this work reveals that the V–Co–Fe catalyst displays an excellent performance in both OER catalytic activity and stability, and may have the potential to be the ideal substitute for noble metal-based catalysts for water splitting to obtain affordable clean energy.

Preparation of Mesoporous Sb-, F-, and In-Doped SnO2 Bulk Powder with High Surface Area for Use as Catalyst Supports in Electrolytic Cells

Abstract: The M-doped tin oxides (M = Sb, F, and In) to be used as catalyst support are synthesized by using templating process with tetradecylamine (TDA) as the template, combined with a hydrothermal (HT) method to improve its thermal stability. The obtained materials are characterized by XRD, SAXS, TEM, EDX, SEM, and BET to study microstructure and physical properties, which have a mesoporous structure, small particle size, and high surface area (125–263 m2 g–1). The materials show an overall conductivity of 0.102–0.295 S cm–1. Repetitive potential cycling is employed to characterize the electrochemical properties and stability. The M-doped tin oxides are highly electrochemical stable compared to carbon black. From the observed results, it can be concluded that the combination of TDA and HT treatment are an effective synthetic method for designing mesoporous M-doped tin oxide as catalyst supports.

Theoretical Investigation of the Reaction Mechanism of the Guaiacol Hydrogenation over a Pt (111) Catalyst

Abstract: The reaction mechanism of the mild hydrogenation of guaiacol over Pt(111) has been investigated by density functional theory calculations and microkinetic modeling. Our model suggests that at 573 K, catechol is the preferred reaction product and that any deoxygenation to, for example, phenol or benzene is at least 4 orders of magnitude slower than the production of catechol. Slow deoxygenation of guaiacol can occur by decarbonylation and possibly by hydrogenation of the phenyl ring followed by C–OH bond cleavage. Direct −OH removal without activation of the phenyl ring is found to be at least 5 orders of magnitude slower. Overall, this study suggests that Pt(111) sites are not active deoxygenation sites and that the experimentally observed deoxygenation activity of Pt catalysts originates likely from the involvement of the catalyst support or Pt step and corner sites.

Medium Effects Are as Important as Catalyst Design for Selectivity in Electrocatalytic Oxygen Reduction by Iron–Porphyrin Complexes

Abstract: Several substituted iron–porphyrin complexes were evaluated for oxygen reduction reaction (ORR) electrocatalysis in different homogeneous and heterogeneous media. The selectivity for four-electron reduction to H2O versus two-electron reduction to H2O2 varies substantially from one medium to another for a given catalyst. In many cases, the influence of the medium in which the catalyst is evaluated has a larger effect on the observed selectivity than the factors attributable to chemical modification of the catalyst. For instance, introduction of potential proton relays has variable effects depending on the catalyst medium. Thus, comparisons of selectivity results from supported and soluble molecular ORR electrocatalysts must be interpreted with caution, as selectivity is a property not only of the catalyst, but also of the larger mesoscale environment beyond the catalyst. Still, in all the direct pairwise comparisons in the same medium, the catalysts with potential proton relays have similar or better selec...

Enhanced catalytic stability through non-conventional synthesis of Ni/SBA-15 for methane dry reforming at low temperatures

Abstract: A non-conventional synthesis route for the preparation of Ni/SBA-15 catalyst for methane dry reforming (MDR), comprising the addition of ascorbic acid as reducing agent, was considered and compared to impregnation and precipitation conventional preparation methods. The catalyst prepared following this novel route evidenced successful confinement of Ni-species inside the pores of SBA-15, both NiO and Ni-phyllosilicates. Due to its particular characteristics, this catalyst showed enhanced activity, selectivity and stability in MDR experiments. Concretely, deactivation of the catalyst was substantially hindered, due to improved selectivity, preferential carbon growth on the external surface of the catalyst, and special ability of the catalyst to favor the formation of amorphous carbon.

Carbon nitride nanosheets decorated with WO3 nanorods: Ultrasonic-assisted facile synthesis and catalytic application in the green manufacture of dialdehydes

Abstract: Carbon nitride nanosheets decorated with WO 3 nanorods (WO 3 /g-C 3 N 4 ) were fabricated via ultrasonic-assisted dispersion and conventional incipient wetness impregnation method. It is found that ultrasonic promoted the formation of g-C 3 N 4 nanosheets efficiently. The promotion effect in the structural evolution and catalytic performance for the rod-like structure of WO 3 caused by g-C 3 N 4 nanosheets were well studied. For the first time, the novel WO 3 /g-C 3 N 4 nanocomposites were used as efficient catalysts in the green process of dialdehydes from the selective oxidation of cycloalkene oxides using H 2 O 2 as a clean oxidant, owing to the high dispersion of active sites and the strong interaction between cycloalkene oxides and the NH or NH 2 groups on the surface of g-C 3 N 4 sheets. Here, C 3 N 4 nanosheets are considered as the catalyst support and co-catalyst as well. The novel nanocomposites are very stable and can be reused for five times without obvious loss of catalytic activity.