Showing papers on "Noble metal published in 2020"

Noble-metal-free Ni2P modified step-scheme SnNb2O6/CdS-diethylenetriamine for photocatalytic hydrogen production under broadband light irradiation

Abstract: Step-scheme (S-scheme) photocatalytic system has been considered as an effective method for solar energy conversion by utilizing broadband solar energy, realizing easy separation of photoexcited carriers and strong redox ability. Herein, the novel ternary Ni2P cocatalysted two-dimensional (2D)/2D SnNb2O6/CdS-diethylenetriamine (SNO/CdS-D) system was designed and fabricated. The S-scheme SNO/CdS-D heterostructure gives photocatalytic hydrogen production of 7808 μmol g−1 h−1, which is about 130.13 and 2.35 times stronger than that of SNO and CdS-D. Further, noble-metal-free Ni2P cocatalyst is decorated into SNO/CdS-D heterostructure, the photocatalytic hydrogen evolution performance could be enhanced to 11,992 μmol g−1 h−1. Additionally, XPS analysis and DFT calculation revealed the carriers moves from CdS-D to SNO and then to Ni2P in the Ni2P-SNO/CdS-D nanocomposite. This work will give a reliable and clear insight into the interface and surface design of the 2D catalysts and offer a broadband photocatalytic hydrogen evolution process without noble metal cocatalysts.

Recent Advances in Noble Metal (Pt, Ru, and Ir)-Based Electrocatalysts for Efficient Hydrogen Evolution Reaction.

Abstract: Noble metal (Pt, Ru, and Ir)-based electrocatalysts are currently considered the most active materials for the hydrogen evolution reaction (HER). Although they have been associated with high cost, easy agglomeration, and poor stability during the HER reaction, recent efforts to intentionally tailor noble-metal-based catalysts have led to promising improvements, with lower cost and superior activity, which are critical to achieving large-scale production of pure hydrogen. In this mini-review, we focus on the recent advances in noble-metal-based HER electrocatalysts. In particular, the synthesis strategies to enhance cost-effectiveness and the catalytic activity for HER are highlighted.

Remarkably catalytic activity in reduction of 4-nitrophenol and methylene blue by Fe3O4@COF supported noble metal nanoparticles

Abstract: Noble metal nanoparticles (NPs) and covalent organic frameworks (COFs) represent two types of the most studied nanomaterials due to their excellent properties and broad applications. Herein, Fe3O4@COF (TAPB-DMTP) core-shell structure was constructed and used as a support for the immobilization of ultrafine Au NPs for the first time. Au NPs (4.0 nm) were in situ synthesized via the post-reduction method with NaBH4 and immobilized homogeneously in shells of Fe3O4@COF. The resultant core-shell structured Fe3O4@COF-Au exhibits remarkably catalytic activities, good thermal and chemical stabilities, and convenient magnetic separability in reduction of 4-nitrophenol (4-NP) and methylene blue (MB) with NaBH4. More importantly, this synthesis strategy is also applicable to other noble metal NPs (for example, Pt and Pd) to construct such multifunctional hybrid nanomaterials for catalysis application.

Recent advances on catalysts for improving hydrocarbon compounds in bio-oil of biomass catalytic pyrolysis

Abstract: This paper reports the progress of catalysts for improving the hydrocarbon compounds in bio-oil obtained from catalytic pyrolysis of biomass. In addition, the effects of the other operating conditions, such as temperature, type of biomass, heating rate, vapors residence time, carrier gas, and hydrogen donor on the yield and properties of bio-oil have been briefly explored. Temperature and catalysts type were found to have major impact on the bio-oil yield and quality. TGA-DTA analysis of biomass revealed that major biomasses pyrolysis zone for high bio-oil yield is in the range of 400–600 °C. Pilot, semi-pilot and large-scale units reported an average temperature of 500 °C for pyrolysis of biomass. The development of advanced catalysts such as zeolite-based catalysts, supported transition and noble metal catalysts, and metal oxide catalysts have been designed to remove the undesired compounds and to increase the hydrocarbon yield in bio-oil. Noble metal supported catalysts produced bio-oil with a low content of oxygenated compounds compared to non-noble metal catalysts; however, their cost and accessibility favor the utilization of non-noble metal supported catalysts.

Three-dimensional carbon foam supported MnO2/Pt for rapid capture and catalytic oxidation of formaldehyde at room temperature

Abstract: Catalytic oxidation of formaldehyde (HCHO) at room temperature is one of the most viable approaches to indoor HCHO pollution abatement. Herein, three-dimensional (3D) carbon foam decorated with Pt/MnO2 nanosheets (Pt/MnO2-CF) was in-situ synthesized for room-temperature catalytic oxidation of HCHO. The 3D Pt/MnO2-CF with a low platinum content of 0.3 wt% exhibited excellent catalytic activity because of its hierarchically porous structure facilitating the diffusion of reactant molecules. Moreover, an abundance of active oxygen species resulting from oxygen vacancies are favorable for HCHO oxidation. In addition, the carbon foam substrate exhibited a very good HCHO adsorption capability, which helps achieve prompt reduction in HCHO concentration in the gas-phase and subsequent complete oxidation of adsorbed HCHO. The combination of adsorption and oxidation was more favorable for oxidative decomposition of HCHO. This work demonstrates that such 3D nanocomposites with low noble metal loading have promising application for indoor HCHO removal and air purification.

Mechanochemical Kilogram-Scale Synthesis of Noble Metal Single-Atom Catalysts

Abstract: Summary Single-atom catalysts (SACs) have attracted broad interest recently due to their superior catalytic properties. However, a facile fabrication method for the large-scale synthesis of SACs is still in demand. This study reports a mechanochemical approach for the mass production of noble metal SACs. The successful formation of atomically dispersed palladium species on zinc oxide (Pd1/ZnO) was verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy. Furthermore, our method exhibited little scaling-up effect on the mass production of Pd1/ZnO at ranges of 10–1,000 g, in which the catalyst structure and catalytic performance were retained. Meanwhile, the versatility of this approach was demonstrated by the large-scale fabrication of Rh and Ru SACs, and Pd1/Cu single-atom alloys. Thus, this promising strategy provides the potential for cost-effective mass production of SACs and subsequently may open a window for their industrial application.

Crystallized RuTe2 as unexpected bifunctional catalyst for overall water splitting

Abstract: Bifunctional catalysis for water splitting is for the first time realized on Ru noble metal in the form of crystallized RuTe2 nanoparticles on graphene Super activity to the state-of-the-art Pt and RuO2 is found for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) because of the high degree of crystallinity, uniform distribution of nanoparticles, and electronic effect in the catalyst system It offers a low cell voltage of 157 V to drive 10 mA cm−2, 100 mV lower than that of Pt/C-RuO2 benchmark electrodes in an alkaline electrolyte, along with a pretty good chemical and structural stability in the strong corrosive environment The theory calculation confirms the superior intermediates adsorption property because of the Ru/Te synergism, and Pt like/RuO2 like character for water splitting reaction It is a very promising catalyst in the alkaline electrolyzer due to the reliable catalytic ability and relatively low price (1/4 Pt)

A tailored oxide interface creates dense Pt single-atom catalysts with high catalytic activity

Abstract: Highly reactive dense Pt single-atoms stabilized on an oxide support can resolve a grand challenge in the economic use of Pt in catalysis. The maximized number density of reaction sites provided by dense Pt single-atoms guarantees the improved catalytic performance of Pt combined with high efficiency. By manipulating the chemical nature of multi-component interfaces, we synthesized CO-tolerant dense Pt single-atoms highly reactive for the CO oxidation reaction, which governs the key steps for chemical energy conversion and emission control. The addition of 1 wt% of Ce to TiO2 support particles creates a CeOx–TiO2 interface that stabilizes Pt single-atoms by strong electronic interactions. Dense Pt single-atoms formed on CeOx/TiO2 oxides exhibit 15.1 times greater specific mass activity toward CO oxidation at 140 °C compared with a bare Pt/TiO2 catalyst. We elaborate how the CeOx–TiO2 interfaces activate the interface-mediated Mars–van Krevelen mechanism of CO oxidation and protect Pt single-atoms from CO-poisoning. Through a comprehensive interpretation of the formation and activation of dense Pt single-atoms using operando X-ray absorption spectroscopy, density functional theory calculations, and experimental catalyst performance tests, we provide a key that enables the catalytic performance of noble metal single-atom catalysts to be optimized by atomic-scale tuning of the metal–support interface.

Pyridinic nitrogen exclusively doped carbon materials as efficient oxygen reduction electrocatalysts for Zn-air batteries

Abstract: Rational design a metal-free catalyst with well-defined structure as alternative of noble metal is highly desirable but challenging to catalyze oxygen reaction for metal–air batteries. In this report, nitrogen with a specific configuration is selectively doped into the carbon skeleton to prepare a graphdiyne-like carbon material, in which one carbon atom in every benzene ring of graphdiyne (GDY) is substituted by pyridinc N (PyN-GDY). Composed by pyridine ring and acetylenic linkers, the PyN-GDY is prepared through a bottom-up strategy using pentaethynylpyridine as the monomer. The as-synthesized PyN-GDY with “defined” molecular structure is an ideal model for addressing the intrinsic activity of active sites at molecular level. It exhibits excellent performance in both alkaline and acidic media as electrochemical catalyst for oxygen reduction reaction (ORR). The PyN-GDY-based Zn-air battery is demonstrated more active and stable than commercial Pt/C-based battery. Density functional theory calculations are used to analyze and determine the possible active sites of PyN-GDY in ORR. The precise construction of specific nitrogen doped carbon material is an effective method to produce efficient catalysts for electrocatalysis.

Bimetallic iron-iridium alloy nanoparticles supported on nickel foam as highly efficient and stable catalyst for overall water splitting at large current density

Abstract: In this work, FeIr bimetallic alloy self-supported on nickel foam is prepared by hydrothermal method, with average particle size of 2.17 nm and the Ir-loading is only 0.936 wt.%. It displays ultralow overpotentials for OER (200 mV) and HER (16.6 mV) at 20 mA cm−2 in alkaline media, which is superior to the ever reported HER catalysts. For overall water splitting, it only needs 1.48 V to derive a current density of 10 mA cm−2, and it also demonstrates an outstanding long-term stability with an ignorable decline in performance after testing 504 h at the current density of 150 mA cm−2. The excellent performance is ascribed to the ultrasmall FeIr alloy, the 3D conductive substrate, and the ethylene-glycol ligand environment facilitates highly efficient HER through hydrogen spillover. Thus, this work undoubtedly provides a promising method for developing ultralow-loading noble metal catalysts with excellent performance at large current density for overall water splitting.

Engineering stable electrocatalysts by synergistic stabilization between carbide cores and Pt shells.

Abstract: Core–shell particles with earth-abundant cores represent an effective design strategy for improving the performance of noble metal catalysts, while simultaneously reducing the content of expensive noble metals1–4. However, the structural and catalytic stabilities of these materials often suffer during the harsh conditions encountered in important reactions, such as the oxygen reduction reaction (ORR)3–5. Here, we demonstrate that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials. In situ, time-resolved experiments showed how the Pt coating protects the normally labile core against oxidation and dissolution, and detailed microscopy studies revealed the dynamics of partially and fully coated core–shell nanoparticles during potential cycling. Particles with complete Pt coverage precisely maintained their core–shell structure and atomic composition during accelerated electrochemical ageing studies consisting of over 10,000 potential cycles. The exceptional durability of fully coated materials highlights the potential of core–shell architectures using earth-abundant transition metal carbide (TMC) and nitride (TMN) cores for future catalytic applications. Using core–shell particles represents an effective design strategy for improving the performance of noble metal catalysts, but their stabilities can suffer during reactions. Atomically thin Pt shells are shown to stabilize titanium tungsten carbide cores, even at highly oxidizing potentials.

Hydrogen Generation upon Nanocatalyzed Hydrolysis of Hydrogen-Rich Boron Derivatives: Recent Developments.

Abstract: ConspectusProduction of hydrogen from nonfossil sources is essential toward the generation of sustainable energy. Hydrogen generation upon hydrolysis of stable hydrogen-rich materials has long been proposed as a possibility of hydrogen disposal on site, because transport of explosive hydrogen gas is dangerous. Hydrolysis of some boron derivatives could rapidly produce large amounts of hydrogen, but this requires the presence of very active catalysts. Indeed, late transition-metal nanocatalysts have recently been developed for the hydrolysis of a few hydrogen-rich precursors.Our research group has focused on the improvement and optimization of highly performing Earth-abundant transition-metal-based nanocatalysts, optimization of remarkable synergies between different metals in nanoalloys, supports including positive synergy with nanoparticles (NPs) for rapid hydrogen generation, comparison between various endo- or exoreceptors working as homogeneous and heterogeneous supports, mechanistic research, and comparison of the nanocatalyzed hydrolysis of several boron hydrides.First, hydrogen production upon hydrolysis of ammonia borane, AB (3 mol H2 per mol AB) was examined with heterogeneous endoreceptors. Thus, a highly performing Ni@ZIF-8 nanocatalyst was found to be superior over other Earth-abundant nanocatalysts and supports. With 85.7 molH2·molcat-1·min-1 at 25 °C, this Ni nanocatalyst surpassed the results of previous Earth-abundant nanocatalysts. The presence of NaOH accelerated the reaction, and a remarkable pH-dependent "on-off" control of the H2 production was established. Bimetallic nanoalloys Ni-Pt@ZIF-8 showed a dramatic volcano effect optimized with a nanoalloy containing 2/3 Ni and 1/3 Pt. The rate reached 600 molH2·molcat-1·min-1 and 2222 molH2·molPt-1·min-1 at 20 °C, which much overtook the performances of both related nanocatalysts Ni@ZIF-8 and Pt@ZIF-8. Next, hydrogen production was also researched via hydrolysis of sodium borohydride (4 mol H2 per mol NaBH4) using nanocatalysts in ZIF-8, and, among Earth-abundant nanocatalysts, Co@ZIF-8 showed the best performance, outperforming previous Co nanocatalysts. For exoreceptors, "click" dendrimers containing triazole ligands on their tripodal tethers were used as supports for homogeneous (semiheterogeneous) catalysis of both AB and NaBH4 hydrolysis. For both reactions, Co was found to be the best Earth-abundant metal, Pt the best noble metal, and Co1Pt1 the best nanoalloy, with synergistic effects. Based on kinetic measurements and kinetic isotope effects for all of these reactions, mechanisms are proposed and the hydrogen produced was further used in tandem reactions. Overall, dramatic triple synergies between these nanocatalyst components have allowed hydrogen release within a few seconds under ambient conditions. These nanocatalyst improvements and mechanistic findings should also inspire further nanocatalyst design in various areas of hydrogen production.

Challenges and opportunities in the bottom-up mechanochemical synthesis of noble metal nanoparticles

Abstract: Mechanochemistry is a promising alternative to solution-based protocols across the chemical sciences, enabling different types of chemistries in solvent-free and environmentally benign conditions. The use of mechanical energy to promote physical and chemical transformations has reached a high level of refinement, allowing for the design of sophisticated molecules and nanostructured materials. Among them, the synthesis of noble metal nanoparticles deserves special attention due to their catalytic applications. In this review, we discuss the recent progress on the development of mechanochemical strategies for the controlled synthesis of noble metal nanostructures. We start by covering the fundamentals of different preparation routes, namely top-down and bottom-up approaches. Next, we focus on the key examples of the mechanochemical synthesis of non-supported and supported metal nanoparticles as well as hybrid nanomaterials containing noble metals. In these examples, in addition to the principles and synthesis mechanisms, their performances in catalysis are discussed. Finally, a perspective of the field is given, where we discuss the opportunities for future work and the challenges of mechanochemical synthesis to produce well-defined noble metal nanoparticles.

Stable and selective electrosynthesis of hydrogen peroxide and the electro-Fenton process on CoSe2 polymorph catalysts

Abstract: Electrochemical synthesis of hydrogen peroxide (H2O2) in acidic solution can enable the electro-Fenton process for decentralized environmental remediation, but robust and inexpensive electrocatalysts for the selective two-electron oxygen reduction reaction (2e− ORR) are lacking. Here, we present a joint computational/experimental study that shows both structural polymorphs of earth-abundant cobalt diselenide (orthorhombic o-CoSe2 and cubic c-CoSe2) are stable against surface oxidation and catalyst leaching due to the weak O* binding to Se sites, are highly active and selective for the 2e− ORR, and deliver higher kinetic current densities for H2O2 production than the state-of-the-art noble metal or single-atom catalysts in acidic solution. o-CoSe2 nanowires directly grown on carbon paper electrodes allow for the steady bulk electrosynthesis of H2O2 in 0.05 M H2SO4 with a practically useful accumulated concentration of 547 ppm, the highest among the reported 2e− ORR catalysts in acidic solution. Such efficient and stable H2O2 electrogeneration further enables the effective electro-Fenton process for model organic pollutant degradation.

Stable Rhodium (IV) Oxide for Alkaline Hydrogen Evolution Reaction

Abstract: Water electrolysis in alkaline electrolyte is an attractive way toward clean hydrogen energy via the hydrogen evolution reaction (HER), whereas the sluggish water dissociation impedes the following hydrogen evolution. Noble metal oxides possess promising capability for catalyzing water dissociation and hydrogen evolution; however, they are never utilized for the HER due to the instability under the reductive potential. Here it is shown that compressive strain can stabilize RhO2 clusters and promote their catalytic activity. To this end, a strawberry-like structure with RhO2 clusters embedded in the surface layer of Rh nanoparticles is engineered, in which the incompatibility between the oxide cluster and the metal substrate causes intensive compressive strain. As such, RhO2 clusters remain stable at a reduction potential up to -0.3 V versus reversible hydrogen electrode and present an alkaline HER activity superior to commercial Pt/C.

C–O bond activation using ultralow loading of noble metal catalysts on moderately reducible oxides

Abstract: Selective C–O activation of multifunctional molecules is essential for many important chemical processes. Although reducible metal oxides are active and selective towards reductive C–O bond scission via the reverse Mars–van Krevelen mechanism, the most active oxides undergo bulk reduction during reaction. Here, motivated by the enhanced oxide reducibility by metals, we report a strategy for C–O bond activation by doping the surface of moderately reducible oxides with an ultralow loading of noble metals. We demonstrate the principle using highly dispersed Pt anchored onto TiO2 for furfuryl alcohol conversion to 2-methylfuran. A combination of density functional theory calculations, catalyst characterization (scanning transmission electron microscopy, electron paramagnetic resonance, Fourier-transform infrared spectroscopy and X-ray absorption spectroscopy), kinetic experiments and microkinetic modelling expose substantial C–O activation rate enhancement, without bulk catalyst reduction or unselective ring hydrogenation. A methodology is introduced to quantify various types of sites, revealing that the cationic redox Pt on the TiO2 surface is more active than metallic sites for C–O bond activation. Reducible metal oxides selectively catalyse the hydrodeoxygenation of C–O bonds in bio-based aromatic molecules, although they show limited performance. Now, using TiO2 as an example, a method is reported to enhance the activity of the oxide by surface doping with an ultralow loading of Pt.

Irreversible accumulated SERS behavior of the molecule-linked silver and silver-doped titanium dioxide hybrid system.

Abstract: In recent years, surface-enhanced Raman scattering (SERS) of a molecule/metal–semiconductor hybrid system has attracted considerable interest and regarded as the synergetic contribution of the electromagnetic and chemical enhancements from the incorporation of noble metal into semiconductor nanomaterials. However, the underlying mechanism is still to be revealed in detail. Herein, we report an irreversible accumulated SERS behavior induced by near-infrared (NIR) light irradiating on a 4-mercaptobenzoic acid linked with silver and silver-doped titanium dioxide (4MBA/Ag/Ag-doped TiO2) hybrid system. With increasing irradiation time, the SERS intensity of 4MBA shows an irreversible exponential increase, and the Raman signal of the Ag/Ag-doped TiO2 substrate displays an exponential decrease. A microscopic understanding of the time-dependent SERS behavior is derived based on the microanalysis of the Ag/Ag-doped TiO2 nanostructure and the molecular dynamics, which is attributed to three factors: (1) higher crystallinity of Ag/Ag-doped TiO2 substrate; (2) photo-induced charge transfer; (3) charge-induced molecular reorientation. The authors report that near-infrared light induces an irreversible accumulated Surface-enhanced Raman scattering (SERS) behavior of a molecule/metal–semiconductor hybrid system. They investigate the underlying mechanism and show that it is attributed to crystallinity, charge transfer and reorientation.

Unveiling reductant chemistry in fabricating noble metal aerogels for superior oxygen evolution and ethanol oxidation.

Abstract: Amongst various porous materials, noble metal aerogels attract wide attention due to their concurrently featured catalytic properties and large surface areas. However, insufficient understanding and investigation of key factors (e.g. reductants and ligands) in the fabrication process limits on-target design, impeding material diversity and available applications. Herein, unveiling multiple roles of reductants, we develop an efficient method, i.e. the excessive-reductant-directed gelation strategy. It enables to integrate ligand chemistry for creating gold aerogels with a record-high specific surface area (59.8 m2 g−1), and to expand the composition to all common noble metals. Moreover, we demonstrate impressive electrocatalytic performance of these aerogels for the ethanol oxidation and oxygen evolution reaction, and discover an unconventional organic-ligand-enhancing effect. The present work not only enriches the composition and structural diversity of noble metal aerogels, but also opens up new dimensions for devising efficient electrocatalysts for broad material systems. Non-efficient gelation methods for noble metal particles limit the development of the corresponding gel materials. Here the authors describe the role of reductants, unlocking ligand chemistry, and largely expanding the composition space of noble metal aerogels for high-performance electrocatalysis.