Showing papers on "Noble metal published in 2012"
TL;DR: In this paper, a variety of bifunctional electrocatalysts with a combination of monofunctional electrodes such as platinum for oxygen reduction and iridium oxide for oxygen evolution for reversible fuel cell applications have been developed.
Abstract: Hydrogen production by electrochemical water electrolysis has received great attention as an alternative technology for energy conversion and storage. The oxygen electrode has a substantial effect on the performance and durability of water electrolyzers and reversible (or regenerative) fuel cells because of its intrinsically slow kinetics for oxygen evolution/reduction and poor durability under harsh operating environments. To improve oxygen kinetics and durability of the electrode, extensive studies for highly active and stable oxygen electrocatalysts have been performed. However, due to the thermodynamic instability of transition metals in acidic media, noble metal compounds have been primarily utilized as electrocatalysts in water electrolyzers and reversible fuel cells. For water electrolyzer applications, single noble metal oxides such as ruthenium oxide and iridium oxide have been studied, and binary or ternary metal oxides have been developed to obtain synergistic effects of each component. On the other hand, a variety of bifunctional electrocatalysts with a combination of monofunctional electrocatalysts such as platinum for oxygen reduction and iridium oxide for oxygen evolution for reversible fuel cell applications have been mainly proposed. Practically, supported iridium oxide-on-platinum, its reverse type, and non-precious metal-supported platinum and iridium bifunctional electrocatalysts have been developed. Recent theoretical calculations and experimental studies in terms of water electrolysis and fuel cell technology suggest the effective ways to cope with current major challenges of cost and durability of oxygen electrocatalysts for technical applications.
479 citations
TL;DR: A review of surface plasmon resonance-mediated photocatalysis can be found in this article, where the authors highlight diverse applications of plasmoric photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting.
Abstract: Harvesting abundant and renewable sunlight in energy production and environmental remediation is an emerging research topic. Indeed, research on solar-driven heterogeneous photocatalysis based on surface plasmon resonance has seen rapid growth and potentially opens a technologically promising avenue that can benefit the sustainable development of global energy and the environment. This review briefly summarizes recent advances in the synthesis and photocatalytic properties of plasmonic composites (e.g., hybrid structures) formed by noble metal (e.g., gold, silver) nanoparticles dispersed on a variety of substrates that are composed of metal oxides, silver halides, graphene oxide, among others. Brief introduction of surface plasmon resonance and the synthesis of noble metal-based composites are given, followed by highlighting diverse applications of plasmonic photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting. Insights into surface plasmon resonance-mediated photocatalysis not only impact the basic science of heterogeneous photocatalysis, but generate new concepts guiding practical technologies such as wastewater treatment, air purification, selective oxidation reactions, selective reduction reactions, and solar-to-hydrogen energy conversion in an energy efficient and environmentally benign approach. This review ends with a summary and perspectives.
464 citations
TL;DR: This study demonstrated that inexpensive, highly reproducible, high performance and scalable air-cathode can be produced by rolling method without using noble metal and expensive binder.
394 citations
TL;DR: In this article, the authors demonstrate the molecular engineering of active sites on a graphene scaffold and demonstrate that the N-doped graphene nanosheets prepared by a high-temperature nitridation procedure represent a novel chemical function of efficiently catalyzing aerobic alcohol oxidation.
Abstract: This work demonstrates the molecular engineering of active sites on a graphene scaffold. It was found that the N-doped graphene nanosheets prepared by a high-temperature nitridation procedure represent a novel chemical function of efficiently catalyzing aerobic alcohol oxidation. Among three types of nitrogen species doped into the graphene lattice—pyridinic N, pyrrolic N, and graphitic N—the graphitic sp2 N species were established to be catalytically active centers for the aerobic oxidation reaction based on good linear correlation with the activity results. Kinetic analysis showed that the N-doped graphene-catalyzed aerobic alcohol oxidation proceeds via a Langmuir–Hinshelwood pathway and has moderate activation energy (56.1 ± 3.5 kJ·mol–1 for the benzyl alcohol oxidation) close to that (51.4 kJ·mol–1) proceeding on the catalyst Ru/Al2O3 reported in literature. An adduct mechanism was proposed to be different remarkably from that occurring on the noble metal catalyst. The possible formation of a sp2 N–...
364 citations
TL;DR: The preparation, characterization, and catalytic activity of supported metal phosphides are reviewed in this article, where the authors show that the surfaces of Ni2P reconstruct to P-rich surfaces.
Abstract: The preparation, characterization, and catalytic activity of supported metal phosphides are reviewed. Reduction of metal compounds together with phosphate is a convenient method to prepare metal phosphides, but requires high temperature. Reduction with phosphite, hypophosphite, or phosphine and the plasma reduction of phosphate can be carried out at lower temperatures, which leads to smaller metal phosphide particles and more active catalysts. Organometallic routes allow the separate synthesis of metal phosphide nanoparticles, which have to be added to the support in a second step. LEED, STM, XPS, and DFT studies have shown that the surfaces of Ni2P reconstruct to P-rich surfaces. The investigation of metal phosphides as catalysts for hydrotreating reactions continues to be a topic of considerable research with recent advances realized in using bimetallic and noble metal phosphides to achieve high activities and tailored selectivities. Finally, hydrodeoxygenation catalysis over metal phosphides is a growing area of research given the need to develop catalysts for upgrading biomass to transportation fuels.
359 citations
TL;DR: This work demonstrates through real space direct visualization and manipulation in combination with X-ray photoelectron spectroscopy and density functional theory calculations the Ag surface-mediated terminal alkyne C(sp)-H bond activation and concomitant homo-coupling in a process formally reminiscent of the classical Glaser-Hay type reaction.
Abstract: The covalent linking of acetylenes presents an important route for the fabrication of novel carbon-based scaffolds and two-dimensional materials distinct from graphene. To date few attempts have been reported to implement this strategy at well-defined interfaces or monolayer templates. Here we demonstrate through real space direct visualization and manipulation in combination with X-ray photoelectron spectroscopy and density functional theory calculations the Ag surface-mediated terminal alkyne C(sp)-H bond activation and concomitant homo-coupling in a process formally reminiscent of the classical Glaser-Hay type reaction. The alkyne homo-coupling takes place on the Ag(111) noble metal surface in ultrahigh vacuum under soft conditions in the absence of conventionally used transition metal catalysts and with volatile H(2) as the only by-product. With the employed multitopic ethynyl species, we demonstrate a hierarchic reaction pathway that affords discrete compounds or polymeric networks featuring a conjugated backbone. This presents a new approach towards on-surface covalent chemistry and the realization of two-dimensional carbon-rich or all-carbon polymers.
344 citations
TL;DR: The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.
Abstract: Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.
339 citations
294 citations
TL;DR: The results suggest that the metal nanoparticles not only play a role in capturing photogenerated electrons, but are strongly involved in the photocatalytic reaction mechanism, and Interestingly, the as-prepared Pd and Au-Pd decorated TiO(2) materials exhibit excellent long-term photoactivity.
Abstract: Noble metal nanoparticles (Au, Pd, Au–Pd alloys) with a narrow size distribution supported on nanocrystalline TiO2 (M/TiO2) have been synthesized via a sol-immobilization route. The effect of metal identity and size on the photocatalytic performance of M/TiO2 has been systematically investigated using phenol as a probe molecule. A different phenol degradation pathway was observed when using M/TiO2 catalysts as compared to pristine TiO2. We propose a mechanism to illustrate how the noble metal nanoparticles enhance the efficiency of phenol decomposition based on photoreduction of p-benzoquinone under anaerobic conditions. Our results suggest that the metal nanoparticles not only play a role in capturing photogenerated electrons, but are strongly involved in the photocatalytic reaction mechanism. The analysis of the reaction intermediates allows us to conclude that on M/TiO2 undesired redox reactions that consume photogenerated radicals are effectively suppressed. The analysis of the final products shows th...
249 citations
TL;DR: Among 18 oxide/noble metal catalysts, TiO(2)/0.1 mol % Pd microspheres showed the highest turnover frequency in NaBH(4) reduction of 4-nitrophenol.
Abstract: Catalytic microspheres: A general approach is demonstrated for the facile preparation of mesoporous metal oxide microspheres loaded with noble metal nanoparticles (see TEM image in the picture). Among 18 oxide/noble metal catalysts, TiO(2)/0.1 mol % Pd microspheres showed the highest turnover frequency in NaBH(4) reduction of 4-nitrophenol (see picture).
243 citations
TL;DR: In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied.
Abstract: Metal decorated graphene materials are highly important for catalysis. In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method. The thermal reductions of metal doped-graphite oxide precursors were carried out in nitrogen and hydrogen atmospheres and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied. The hybrids exfoliated in nitrogen atmosphere contained a higher amount of oxygen-containing groups and lower density of defects on their surfaces than hybrids exfoliated in hydrogen atmosphere. The metals significantly affected the electrochemical behavior and catalysis of compounds that are important in energy production and storage and in electrochemical sensing. Research in the field of energy storage and production, electrochemical sensing and biosensing as well as biomedical devices can take advantage of the properties and catalytic capabilities of the metal doped graphene hybrids.
TL;DR: Hydrous hydrazine (N2H4·H2O) is considered as a promising liquid hydrogen storage material owing to the high content of hydrogen and the advantage of CO-free H2 produced.
Abstract: Storing hydrogen safely and efficiently is one of the major technological barriers preventing the widespread application of hydrogen-fueled cells, such as proton exchange membrane fuel cells (PEMFCs). Hydrous hydrazine (N2H4·H2O) is considered as a promising liquid hydrogen storage material owing to the high content of hydrogen (7.9%) and the advantage of CO-free H2 produced. [1] In particular, hydrous hydrazine offers great potential as a hydrogen storage material for some special applications, such as unmanned space vehicles and submarine power sources, where hydrazine is usually used as a propellant. The decomposition of hydrazine proceeds by two typical reaction routes:
TL;DR: In this paper, the most recent progress of both synthesis and applications of noble metal nanocrystals with high-energy facets is summarized, with an emphasis on surface-enhanced properties and applications.
TL;DR: Self-assembly of noble metal nanocrystals has become one of the hottest fields in nanoscience due to their unique/strong interactions with extra electromagnetic field, which are known as localized surface plasmon resonance as discussed by the authors.
TL;DR: In this article, various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts.
TL;DR: In this paper, the effects of nitrogen doping and noble metal loading were investigated in detail for CO 2 photoreduction by water in gas phase, and it was found that the loading of Pt also promoted the transformation of catalyst associated carbon residues to methane.
Abstract: Nitrogen-doped mesoporous TiO 2 photocatalysts were developed for CO 2 photoreduction by water in gas phase. The effects of nitrogen doping and noble metal loading were investigated in detail. The characteristics of samples were investigated by techniques, such as XRD, FT-IR, TEM, XPS, nitrogen adsorption–desorption, and UV–vis diffuse reflectance spectroscopy. The loading of noble metals (i.e., Pt, Au, and Ag) generally improved the photocatalytic activity, and the efficiency follows the order: Pt > Au > Ag. It was found that the loading of Pt also promoted the transformation of catalyst associated carbon residues to methane. With unique properties, such as the mesoporous structure, light absorption, and the electron transfer character, the nitrogen-doped mesoporous TiO 2 samples showed good activity for CO 2 photoreduction to methane under visible light. The optimum loading amount of Pt was 0.2 wt.%, and the optimum doping amount of N was 0.84% on the basis of the lattice oxygen atoms. Aspects such as the origination of visible light sensitivity in terms of nitrogen doping, the effect of noble metal loading, and the reaction mechanism were also discussed.
TL;DR: In this paper, the etching mechanism of metal-assisted chemical etching using a contiguous metal thin film is investigated, especially the mass transport of reactants and byproducts, and several models of metal assisted chemical etch using a metal film are presented.
Abstract: Metal-assisted chemical etching is a relatively new top-down approach allowing a highly controlled and precise fabrication of Si and Si/Ge superlattice nanowires. It is a simple method with the ability to tailor diverse nanowire parameters like diameter, length, density, orientation, doping level, doping type, and morphology. In a typical metal-assisted chemical etching procedure, a Si substrate is covered by a lithographic noble metal film and etched in a solution containing HF and an oxidant (typically H2O2). In general, the function of the metal is to catalyze the reduction of H2O2, which delivers electronic holes necessary for the oxidation and subsequent dissolution of the Si oxide by HF. However, the details of the etching process using contiguous metal thin films, especially the mass transport of reactants and byproducts are still not well understood. In this study, the etching mechanism was systematically investigated. Several models of metal-assisted chemical etching using a contiguous metal film...
TL;DR: In this article, the authors describe the successful fabrication of silver nanoparticles (Ag NPs) in situ grown on magnetically separable alginate-based biohydrogels (Ag@AMH) by an environmentally friendly light-driven approach.
Abstract: Noble metal nanocatalysts are one of the most promising candidates for various catalysis applications. However, their high surface energy undesirably causes serious stability problems, which remarkably decreases the intrinsic catalytic activity. In this paper, for the first time, we describe the successful fabrication of silver nanoparticles (Ag NPs) in situ grown on magnetically separable alginate-based biohydrogels (Ag@AMH) by an environmentally friendly light-driven approach. In the presence of alginate biopolymers, silver ions can be readily adsorbed and subsequently photoreduced to metallic Ag NPs on the biohydrogels. These Ag@AMH catalysts were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) techniques. The resulting Ag@AMH exhibited excellent and durable activity for the catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous solution, which can be recycled for three successive cycles of the reaction with a conversion efficiency of more than 99%. Such Ag@AMH were thus expected to have the potential as a highly efficient, cost-effective and eco-friendly heterogeneous catalyst for industrial applications.
TL;DR: In this article, the Adams method was used for solid polymer electrolyte (SPE) water electrolysis and the physicochemical properties of the catalyst were characterized via X-ray diffraction (XRD) and transmission electron microscopy (TEM).
TL;DR: In this article, a critical review of gold, silver and platinum nanoparticles with relevance to the above parameters is presented, including how these nanomaterials interact with the cells at the molecular level, how their biodistribution and pharmacokinetics influenced by their surface and routes of administration, mechanism of their detoxification and clearance and their therapeutic efficacy in appropriate disease model.
Abstract: Biomedical nanotechnology is an evolving field having enormous potential to positively impact the health care system. Important biomedical applications of nanotechnology that may have potential clinical applications include targeted drug delivery, detection/diagnosis and imaging. Basic understanding of how nanomaterials, the building blocks of nanotechnology, interact with the cells and their biological consequences are beginning to evolve. Noble metal nanoparticles such as gold, silver and platinum are particularly interesting due to their size and shape dependent unique optoelectronic properties. These noble metal nanoparticles, particularly of gold, have elicited a lot of interest for important biomedical applications because of their ease of synthesis, characterization and surface functionalization. Furthermore, recent investigations are demonstrating another promising application of these nanomaterials as self-therapeutics. To realize the potential promise of these unique inorganic nanomaterials for future clinical translation, it is of utmost importance to understand a few critical parameters; (i) how these nanomaterials interact with the cells at the molecular level; (ii) how their biodistribution and pharmacokinetics influenced by their surface and routes of administration; (iii) mechanism of their detoxification and clearance and (iv) their therapeutic efficacy in appropriate disease model. Thus in this critical review, we will discuss the various clinical applications of gold, silver and platinum nanoparticles with relevance to above parameters. We will also mention various routes of synthesis of these noble metal nanoparticles. However, before we discuss present research, we will also look into the past. We need to understand the discoveries made before us in order to further our knowledge and technological development (318 references).
TL;DR: In this article, the synthesis, characterization, and catalytic performance of Pt supported on PTA encapsulated in a metal organic framework (MOF) are reported, where the highly dispersed Keggin units of PTA in NH 2 -MIL-101(Al), synthesized in one step, act as anchoring sites for the Pt precursor species.
TL;DR: In this article, the authors presented the synthesis of chemically derived graphene and noble metal composites with coal as the starting material by means of catalytic graphitization, chemical oxidation, and dielectric barrier discharge (DBD) plasma-assisted deoxygenation.
Abstract: Coal has been used as an important resource for the production of chemicals, conventional carbon materials, as well as carbon nanomaterials with novel structures, in addition to its main utilization in the energy field. In this work, we present the synthesis of chemically derived graphene and graphene–noble metal composites with coal as the starting material by means of catalytic graphitization, chemical oxidation, and dielectric barrier discharge (DBD) plasma-assisted deoxygenation. It is found that the graphitization degree of the coal-derived carbon remarkably affects the properties of graphene obtained from chemical exfoliation, and high crystallinity of coal-derived carbon is essential for the preparation of high-quality graphene sheets (GS). GS decorated with highly dispersed noble metallic nanoparticles (NP) on their surface (NP/GS) were successfully fabricated via simultaneous reduction of graphite oxide (GO) and noble metal salts by H2 DBD plasma technique. The electrochemical performance of the ...
TL;DR: Study shows that supported Ag and Au NPs may be employed in sustainable environmental remediation, as they can be used at room temperature in aqueous solutions without the use of additional stimulus such as UV light.
Abstract: Application of nanoparticles (NPs) in environmental remediation such as water purification requires a detailed understanding of the mechanistic aspects of the interaction between the species involved. Here, an attempt was made to understand the chemistry of noble metal nanoparticle–pesticide interaction, as these nanosystems are being used extensively for water purification. Our model pesticide, chlorpyrifos (CP), belonging to the organophosphorothioate group, is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl thiophosphate at room temperature over Ag and Au NPs, in supported and unsupported forms. The degradation products were characterized by absorption spectroscopy and electrospray ionization mass spectrometry (ESI MS). These were further confirmed by ESI tandem mass spectrometry. The interaction of CP with NP surfaces was investigated using transmission electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS rev...
TL;DR: In this paper, a plate-like anatase TiO2 mesocrystal superstructures and noble metal (Au, Pt) nanoparticles were preferentially photodeposited on the edge of the mesocrystals and the electron transport and photocatalytic properties of the novel nanocomposites were subsequently studied.
Abstract: Metal–semiconductor nanocomposites have been widely employed for designing efficient optoelectronic devices and catalysts. The performance of such nanocomposites is significantly influenced by both the method of preparation and the electronic and morphological structures of metals and semiconductors. Here, we have synthesized novel nanocomposites containing plate-like anatase TiO2 mesocrystal superstructures and noble metal (Au, Pt) nanoparticles. These metal nanoparticles were preferentially photodeposited on the edge of TiO2 mesocrystals. The electron transport and photocatalytic properties of the novel nanocomposites were subsequently studied. Single-molecule fluorescence spectroscopy measurements on a single particle directly revealed that most of the photogenerated electrons could migrate from the dominant surface to the edge of the TiO2 mesocrystal with the reduction reactions mainly occurring at its lateral surfaces containing {101} facets. The loading of metal nanoparticles on the superstructure o...
TL;DR: Among these catalysts, the PtPd-based composites exhibited the highest activity and resistance to poisoning during the catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH(4).
Abstract: A simple, efficient, and general approach was developed to selectively deposit noble metal (Pt, Pd, or PtPd) nanoparticles 35 nm in size on magnetite/graphene composites. The biomolecule L-lysine with two kinds of functional groups (NH2 and COOH) played the key role of connecter between noble metals and Fe3O4/graphene composites. These composites were characterized by TEM, XRD, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results indicated that the noble metals are mostly dispersed on the magnetite surfaces of the composites. The as-obtained composites are ideal recyclable catalysts for liquid-phase reactions owing to their stability and efficient magnetic separation. Among these catalysts, the PtPd-based composites exhibited the highest activity and resistance to poisoning during the catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH4. Such hybrid catalysts obtained by this simple, efficient method are expected to find use in industrial applications, where separation and recycling are critically required to reduce cost and waste production.
TL;DR: A stable body-centred tetragonal phase is observed in silver nanoparticles with fivefold twinning even at ambient conditions, indicating that the nanoparticle is composed of a highly strained core encapsulated in a less-strained sheath that helps stabilize the strained core.
Abstract: Crystallization of noble metal atoms usually leads to the highly symmetric face-centred cubic phase that represents the thermodynamically stable structure. Introducing defective microstructures into a metal crystal lattice may induce distortions to form non-face-centered cubic phases when the lateral dimensions of objects decrease down to nanometre scale. However, stable non-face-centered cubic phases have not been reported in noble metal nanoparticles. Here we report that a stable body-centred tetragonal phase is observed in silver nanoparticles with fivefold twinning even at ambient conditions. The body-centered tetragonal phase originates from the distortion of cubic silver lattices due to internal strains in the twinned nanoparticles. The lattice distortion in the centre of such a nanoparticle is larger than that in the surfaces, indicating that the nanoparticle is composed of a highly strained core encapsulated in a less-strained sheath that helps stabilize the strained core.
TL;DR: In this paper, Ni-based (over MgO and Al 2 O 3 ) and noble metal-based catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors.
TL;DR: In this article, a cobalt-free and noble metal-free dual-phase oxygen-transporting membrane with a composition of 40 wt % Pr0.6Sr0.4FeO3−δ−60 wt% Ce0.9Pr0.1O2−ε (40PSFO-60CPO) has been successfully developed via an in situ one-pot one-step glycine-nitrate combustion process.
Abstract: A novel cobalt-free and noble metal-free dual-phase oxygen-transporting membrane with a composition of 40 wt % Pr0.6Sr0.4FeO3−δ–60 wt % Ce0.9Pr0.1O2−δ (40PSFO–60CPO) has been successfully developed via an in situ one-pot one-step glycine-nitrate combustion process. In situ XRD demonstrated that the 40PSFO–60CPO dual-phase membrane shows a good phase stability not only in air but also in 50 vol % CO2/50 vol % N2 atmosphere. When using pure He or pure CO2 as sweep gases, at 950 °C steady oxygen permeation fluxes of 0.26 cm3 min–1 cm–2 and 0.18 cm3 min–1 cm–2 are obtained through the 40PSFO–60CPO dual-phase membrane. The partial oxidation of methane (POM) to syngas was also successfully investigated in the 40PSFO–60CPO dual-phase membrane reactor. Methane conversion was found to be higher than 99.0% with 97.0% CO selectivity and 4.4 cm3 min–1 cm–2 oxygen permeation flux in steady state at 950 °C. Our dual-phase membrane - without any noble metals such as Ag, Pd or easily reducible metals oxides of Co or Ni -...
TL;DR: In this paper, a colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensional ordered macroporous (3DOM) Au/CeO 2 catalyst, which possesses well defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at ∼75°C.
Abstract: A colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensionally ordered macroporous (3DOM) Au/CeO 2 catalyst. The resultant Au/CeO 2 catalyst possesses well-defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at ∼75 °C. The catalytic mechanism of HCHO catalytic oxidation over 3DOM Au/CeO 2 catalyst was systematically investigated by means of gas chromatograph (GC), H 2 -temperature programmed reduction (H 2 -TPR), temperature programmed surface reaction (TPSR), CO 2 -temperature programmed desorption (TPD), and Fourier transform infra-red (FT-IR) spectroscopy. GC results indicate that HCOOH intermediate is generated during HCHO catalytic oxidation. TPD and TPSR tests show that the weak absorption ability of CO 2 over 3DOM Au/CeO 2 catalyst and the existence of Au active species in ionic and metallic states in 3DOM Au/CeO 2 catalyst largely improve the catalytic activity, favoring the enhanced HCHO catalytic oxidation. FT-IR tests prove that the carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO 2 catalyst during HCHO catalytic oxidation may account for its deactivation. Based on the above investigation, a new catalytic mechanism of enhanced HCHO catalytic oxidation over 3DOM Au/CeO 2 catalyst is proposed. The mechanism may afford the scientific guidance for preparing high efficiency oxide supported noble metal catalysts and present a solution for solving their deactivation problem.
TL;DR: In this paper, the conversion of guaiacol catalyzed by Pt/MgO in the presence of H2 was investigated with a flow reactor at 573 K and 140 KPa.
Abstract: The conversion of guaiacol catalyzed by Pt/MgO in the presence of H2 was investigated with a flow reactor at 573 K and 140 kPa. Among the dozens of reaction products identified by gas chromatography (GC) and GC/mass spectrometry, the predominant ones were phenol, catechol, and (surprisingly) cyclopentanone, with others including methane, n-butane, butenes, n-pentane, and carbon monoxide. The predominant reactions were hydrodeoxygenation (with about 70 % of the guaiacol that was converted forming products that were reduced in oxygen). In contrast, when the catalyst incorporated an acidic support, Pt/γ-Al2O3, other reactions became kinetically significant, exemplified by transalkylation, and the selectivity to deoxygenated products was reduced to about half the value observed with Pt/MgO at guaiacol conversions in the range of about 6–20 %. Pt/MgO underwent deactivation less rapidly than Pt/γ-Al2O3, consistent with a lower rate of coke formation and with observations by scanning transmission electron microscopy showing that the average platinum cluster diameter, approximately 1–2 nm in each catalyst, did not change significantly during operation. The results point to the advantages of basic supports for noble metal hydrodeoxygenation catalysts. .