Showing papers on "Catalyst support published in 2017"

An efficient and pH-universal ruthenium-based catalyst for the hydrogen evolution reaction

Abstract: Ruthenium nanoparticles homogeneously dispersed in a nitrogenated, two-dimensional carbon matrix show high turnover frequency and small overpotential for hydrogen evolution reaction both in acidic and alkaline media. The hydrogen evolution reaction (HER) is a crucial step in electrochemical water splitting and demands an efficient, durable and cheap catalyst if it is to succeed in real applications1,2,3. For an energy-efficient HER, a catalyst must be able to trigger proton reduction with minimal overpotential4 and have fast kinetics5,6,7,8,9. The most efficient catalysts in acidic media are platinum-based, as the strength of the Pt–H bond10 is associated with the fastest reaction rate for the HER11,12. The use of platinum, however, raises issues linked to cost and stability in non-acidic media. Recently, non-precious-metal-based catalysts have been reported, but these are susceptible to acid corrosion and are typically much inferior to Pt-based catalysts, exhibiting higher overpotentials and lower stability13,14,15. As a cheaper alternative to platinum, ruthenium possesses a similar bond strength with hydrogen (∼65 kcal mol–1)16, but has never been studied as a viable alternative for a HER catalyst. Here, we report a Ru-based catalyst for the HER that can operate both in acidic and alkaline media. Our catalyst is made of Ru nanoparticles dispersed within a nitrogenated holey two-dimensional carbon structure (Ru@C2N). The Ru@C2N electrocatalyst exhibits high turnover frequencies at 25 mV (0.67 H2 s−1 in 0.5 M H2SO4 solution; 0.75 H2 s−1 in 1.0 M KOH solution) and small overpotentials at 10 mA cm–2 (13.5 mV in 0.5 M H2SO4 solution; 17.0 mV in 1.0 M KOH solution) as well as superior stability in both acidic and alkaline media. These performances are comparable to, or even better than, the Pt/C catalyst for the HER.

Catalyst support effects on hydrogen spillover

Abstract: The mechanism of hydrogen spillover is described using a precisely nanofabricated model system, explaining why it is slower on an aluminum oxide catalyst support than on a titanium oxide catalyst support.

Tracking Catalyst Redox States and Reaction Dynamics in Ni-Fe Oxyhydroxide Oxygen Evolution Reaction Electrocatalysts: The Role of Catalyst Support and Electrolyte pH.

Abstract: Ni–Fe oxyhydroxides are the most active known electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes and are therefore of great scientific and technological importance in the context of electrochemical energy conversion. Here we uncover, investigate, and discuss previously unaddressed effects of conductive supports and the electrolyte pH on the Ni–Fe(OOH) catalyst redox behavior and catalytic OER activity, combining in situ UV–vis spectro-electrochemistry, operando electrochemical mass spectrometry (DEMS), and in situ cryo X-ray absorption spectroscopy (XAS). Supports and pH > 13 strongly enhanced the precatalytic voltammetric charge of the Ni–Fe oxyhydroxide redox peak couple, shifted them more cathodically, and caused a 2–3-fold increase in the catalytic OER activity. Analysis of DEMS-based faradaic oxygen efficiency and electrochemical UV–vis traces consistently confirmed our voltammetric observations, evidencing both a more cathodic O2 release and a more cathodic onset of Ni...

A Review on Bimetallic Nickel‐Based Catalysts for CO2 Reforming of Methane

Abstract: In recent years, CO2 reforming of methane (dry reforming of methane, DRM) has become an attractive research area because it converts two major greenhouse gasses into syngas (CO and H2 ), which can be directly used as fuel or feedstock for the chemical industry. Ni-based catalysts have been extensively used for DRM because of its low cost and good activity. A major concern with Ni-based catalysts in DRM is severe carbon deposition leading to catalyst deactivation, and a lot of effort has been put into the design and synthesis of stable Ni catalysts with high carbon resistance. One effective and practical strategy is to introduce a second metal to obtain bimetallic Ni-based catalysts. The synergistic effect between Ni and the second metal has been shown to increase the carbon resistance of the catalyst significantly. In this review, a detailed discussion on the development of bimetallic Ni-based catalysts for DRM including nickel alloyed with noble metals (Pt, Ru, Ir etc.) and transition metals (Co, Fe, Cu) is presented. Special emphasis has been provided on the underlying principles that lead to synergistic effects and enhance catalyst performance. Finally, an outlook is presented for the future development of Ni-based bimetallic catalysts.

Metal/Porous Carbon Composites for Heterogeneous Catalysis: Old Catalysts with Improved Performance Promoted by N-Doping

Abstract: Developing novel and efficient catalysts is always an important theme for heterogeneous catalysis from fundamental and applied research points of view. In the past, carbon materials were used as supports for numerous heterogeneous catalysts because of their fascinating properties including high surface areas, tunable porosity, and functionality. Recently, the newly emerging N-doped carbon-supported metal catalysts have arguably experienced great progress and brought the most attention over the last decades in view of the fact that nitrogen doping can tailor the properties of carbon for various applications of interest. Compared with pristine carbon-supported metal catalysts, these catalysts normally show superior catalytic performance in many heterogeneous catalytic reactions because of the introduced various metal–support interactions from N doping. In this Perspective, we focus on the fabrication methods for N-doped carbon-supported metal catalysts and the catalytic application of these fascinating cata...

Support Effects in Single-Atom Platinum Catalysts for Electrochemical Oxygen Reduction

Abstract: Single-atom catalysts (SACs) provide an ideal platform for reducing noble-metal usage. SACs also exhibit unusual catalytic properties due to the absence of a metal surface. The role of the support may have a significant effect on the catalytic properties, similar to that of the ligand molecules in homogeneous catalysts. Here, the support effect was demonstrated by preparing a single-atom platinum catalyst on two different supports: titanium carbide (Pt1/TiC) and titanium nitride (Pt1/TiN). The formation of single-atom Pt was confirmed by STEM, EXAFS, and in situ IR spectroscopy. Pt1/TiC showed higher activity, selectivity, and stability for electrochemical H2O2 production than Pt1/TiN. Density functional theory calculations presented that oxygen species have strong affinity into Pt1/TiN, possibly acting as surface poisoning species, and Pt1/TiC preserves oxygen–oxygen bonds more with higher selectivity toward H2O2 production. This work clearly shows that the support in SACs actively participates in the su...

Low-Temperature Hydrogenation of Carbon Dioxide to Methanol with a Homogeneous Cobalt Catalyst

Abstract: Herein we describe the first homogeneous non-noble metal catalyst for the hydrogenation of CO2 to methanol. The catalyst is formed in situ from [Co(acac)3], Triphos, and HNTf2 and enables the reaction to be performed at 100 °C without a decrease in activity. Kinetic studies suggest an inner-sphere mechanism, and in situ NMR and MS experiments reveal the formation of the active catalyst through slow removal of the acetylacetonate ligands.

Ethanol steam reforming for hydrogen production: Latest and effective catalyst modification strategies to minimize carbonaceous deactivation

Abstract: Hydrogen is being contemplated as the future fuel in view of the abundant availability of hydrogen bearing substances in nature, its high energy content (120.7 kJ/g), and its combustion without creating any environmental pollution. Pollution free sources for hydrogen generation and efficient conversion to useful energy are the two important factors controlling the development of hydrogen economy. Out of various liquid hydrogen sources, ethanol is a sustainable candidate because of its renewable nature, increasing availability, biodegradable nature, low toxicity, and ease of transport. It can be easily converted to a hydrogen rich mixture through catalytic steam reforming process. Further, ethanol steam reforming (ESR) is thermodynamically feasible and does not cause catalyst poisoning due to complete absence of S-impurities. However, the carbonaceous deposition during ESR is still an issue to make it sustainable for hydrogen generation. This review contains all parallel possible reactions besides the desired reactions, which can promote carbonaceous deposition over catalyst surface with respect to temperature. The role of operating conditions such as water and ethanol feed ratio and temperature with carbon generation were interrelated. The characterization of different carbon forms synthesized during ESR and the possible role of active catalyst into carbon synthesis mechanism was also considered. The contribution of precursor used for catalyst preparation, the role of active metals, the interaction between active metals for bimetallic catalyst, different kind of support prominently studied for ESR and their structural behaviors were also correlated. This review makes an attempt to critically summarize the recent strategies used to reduce the carbonaceous deactivation of catalyst during ESR on the basis of available literature survey. The focus of the review is catalyst deactivation due to carbonaceous deposition during reforming and possible strategies used to control the deactivation process during ESR.

Highly dispersed TiO2 nanocrystals and carbon dots on reduced graphene oxide: Ternary nanocomposites for accelerated photocatalytic water disinfection

Abstract: Graphene is widely used as a catalyst support for improved charge separation in TiO2 photocatalysis. However, the surface oxygen reduction activity of TiO2/graphene might be hindered due to the electron storage ability of graphene. In this study, highly dispersed TiO2 and carbon dots (C-dots) co-decorated reduced graphene oxide (CTR) is synthesized via a simple hydrothermal reaction using TiCl4 and glucose. Transmission electron microscope, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis and Fourier transform IR spectroscopy are employed to characterize the CTR nanocomposite. The comparison experiment confirmed that C-dots were sourced from the carbonization of glucose. Glucose and TiCl4 which are mutual dispersants, are critical for forming highly dispersed and uniform-sized C-dots and TiO2 nanocrystals. With well dispersed TiO2 and C-dots at separated sites of reduced graphene oxide surface, CTR shows enhanced photocatalytic bacterial inactivation performance under simulated solar light. As confirmed by the reactive oxygen species production, the generation of superoxide anion (O2−) and hydrogen peroxide (H2O2) is improved. The electrochemical characterization reveals that charge separation in CTR photocatalysis is also promoted. Taken together, the concurrently improved charge separation and surface oxygen reduction activity contribute to an accelerated photocatalytic bacteria inactivation process.

Hybrid Catalysis Enabling Room-Temperature Hydrogen Gas Release from N-Heterocycles and Tetrahydronaphthalenes

Abstract: Hybrid catalyst systems to achieve acceptorless dehydrogenation of N-heterocycles and tetrahydronaphthalenes—model substrates for liquid organic hydrogen carriers—were developed. A binary hybrid catalysis comprising an acridinium photoredox catalyst and a Pd metal catalyst was effective for the dehydrogenation of N-heterocycles, whereas a ternary hybrid catalysis comprising an acridinium photoredox catalyst, a Pd metal catalyst, and a thiophosphoric imide organocatalyst achieved dehydrogenation of tetrahydronaphthalenes. These hybrid catalyst systems allowed for 2 molar equiv of H2 gas release from six-membered N-heterocycles and tetrahydronaphthalenes under mild conditions, i.e., visible light irradiation at rt. The combined use of two or three different catalyst types was essential for the catalytic activity.

A novel strategy for the synthesis of sulfur-doped carbon nanotubes as a highly efficient Pt catalyst support toward the methanol oxidation reaction

Abstract: Doped nanocarbon materials (e.g., carbon nanotubes, graphene) are considered as effective electrocatalyst supports for fuel cells, and their electrochemical properties are closely related to the synthetic methods and the types of doping elements. In the current paper, we report a novel approach to synthesize sulfur-doped multi-walled carbon nanotubes (S-MWCNTs) as a highly efficient support material for Pt nanoparticle catalysts. The S-MWCNTs are obtained by annealing poly(3,4-ethylenedioxythiophene) (PEDOT) functionalized multi-walled carbon nanotubes at 800 °C. The prepared nanohybrids were physically characterized by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It has been found that the doping of sulfur into MWCNTs could significantly improve the dispersion of supported Pt nanoparticles of 2.37 nm in size and increase the electrochemically active surface area (ECSA, 161.4 m2 g−1). The doped sulfur atoms not only provide uniformly dispersed anchoring sites for the deposition of Pt nanoparticles on the surface of MWCNTs but also enhance the electron transfer interaction between Pt nanoparticles and the S-MWCNT support. The electrochemical properties of the catalysts were evaluated by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The results demonstrate that the as-prepared Pt/S-MWCNTs exhibit much higher electrocatalytic activity, long-term durability and CO-tolerance ability for the methanol oxidation reaction (MOR) compared to the undoped MWCNT supported Pt and commercial Pt/C catalysts.

A novel nickel-based structured catalyst for CO2 methanation: A honeycomb-type Ni/CeO2 catalyst to transform greenhouse gas into useful resources

Abstract: The purpose of this study is to construct a honeycomb-type structured catalyst with a high methanation performance to effectively transform CO2 to CH4. To select the best methanation component for structuring, a 10 wt% Ni-loaded granular catalyst was prepared by evaporation to dryness using Al2O3, TiO2, ZrO2, Y2O3, MgO and CeO2 as the support materials. The granular Ni/CeO2 catalyst displayed the highest activity at 200–500 °C, while the granular Ni/Al2O3, Ni/MgO and Ni/TiO2 catalysts showed low CO2 conversions. The variable affecting the Ni/CeO2 catalyst having a high performance would be related to the large amount of adsorbed CO2 and the production of many chemical species that originated from the CO2 on the surface. The structured catalyst with the Ni/CeO2 component was prepared by a wash-coating method on an aluminum substrate with a honeycomb-fin configuration. The prepared catalyst showed a high methanation performance, indicating that the cell density and the configuration of the honeycomb-fin clearly influenced the performance. Especially, the structured catalyst with the stacked-type-fin enhanced the methanation performance that improved the mass transfer properties in the reaction field. Furthermore, the structured Ni/CeO2 catalyst showed a steady catalytic performance that maintained the high activity and the high selectivity during a durability test at 350 °C. The honeycomb-type catalyst developed in this study has the potential to be a practicable catalyst for producing energy resources from CO2.

Application of biochar-based catalysts in biomass upgrading: a review

Abstract: Biochar is a low-cost carbon-rich material derived from the thermochemical degradation of biomass. Due to its unique chemical structure, biochar with a large surface area and tailored surface functional groups can be easily prepared by activation and/or functionalization, and shows great potential to be used as a versatile catalyst and/or catalyst support in many chemical processes. However, the application of biochars as versatile catalysts and/or catalyst supports for biomass upgrading has not been systematically overviewed so far. In this work, the formation of pyrochar and hydrochar is proposed, and the activation and/or functionalization of biochar are also included. Subsequently, the application of biochar-based catalysts in biomass upgrading, including biochar-based solid acids for biomass hydrolysis and dehydration, biochar-based catalysts for biodiesel production, and biochars as catalyst supports for biomass pyrolysis, gasification, and bio-oil upgrading, are discussed in detail.

Graphdiyne: A Promising Catalyst–Support To Stabilize Cobalt Nanoparticles for Oxygen Evolution

Abstract: Graphdiyne (GDY), with highly π-conjugated structure of sp2- and sp-hybridized carbons, has recently appeared as an allotropic form of carbon nanomaterials. However, the application of this material is far behind its sister graphene. Herein, we attempt to use GDY as catalyst–support to stabilize cobalt nanoparticles for oxygen evolution, which is considered as the bottleneck for water splitting. In terms of close interaction between metal ions and alkyne π-conjugated networks, the self-supported electrode is made in situ by a facile chemical reduction of Co2+ salt precursor in aqueous solution. The prepared 3D Cu@GDY/Co electrode shows high OER electrocatalytic activity with a small overpotential of nearly 0.3 V and a large unit mass activity of 413 A g–1 at 1.60 V vs RHE. In the course of 4 h electrolysis, the electrode maintains the relatively constant current density. Our results indicate that the GDY is a promising catalyst–support to stabilize metal NPs for oxygen evolution.

Trends in Adhesion Energies of Metal Nanoparticles on Oxide Surfaces: Understanding Support Effects in Catalysis and Nanotechnology.

Abstract: Nanoparticles on surfaces are ubiquitous in nanotechnologies, especially in catalysis, where metal nanoparticles anchored to oxide supports are widely used to produce and use fuels and chemicals, and in pollution abatement. We show that for hemispherical metal particles of the same diameter, D, the chemical potentials of the metal atoms in the particles (μM) differ between two supports by approximately −2(Eadh,A – Eadh,B)Vm/D, where Ead,i is the adhesion energy between the metal and support i, and Vm is the molar volume of the bulk metal. This is consistent with calorimetric measurements of metal vapor adsorption energies onto clean oxide surfaces where the metal grows as 3D particles, which proved that μM increases with decreasing particle size below 6 nm and, for a given size, decreases with Eadh. Since catalytic activity and sintering rates correlate with metal chemical potential, it is thus crucial to understand what properties of catalyst materials control metal/oxide adhesion energies. Trends in how...

Interfaces in Heterogeneous Catalysts: Advancing Mechanistic Understanding through Atomic-Scale Measurements.

Abstract: ConspectusDeveloping novel catalysts with high efficiency and selectivity is critical for enabling future clean energy conversion technologies. Interfaces in catalyst systems have long been considered the most critical factor in controlling catalytic reaction mechanisms. Interfaces include not only the catalyst surface but also interfaces within catalyst particles and those formed by constructing heterogeneous catalysts. The atomic and electronic structures of catalytic surfaces govern the kinetics of binding and release of reactant molecules from surface atoms. Interfaces within catalysts are introduced to enhance the intrinsic activity and stability of the catalyst by tuning the surface atomic and chemical structures. Examples include interfaces between the core and shell, twin or domain boundaries, or phase boundaries within single catalyst particles. In supported catalyst nanoparticles (NPs), the interface between the metallic NP and support serves as a critical tuning factor for enhancing catalytic a...

Carbon dioxide hydrogenation over nickel-, ruthenium-, and copper-based catalysts: Review of kinetics and mechanism

Abstract: This study critically reviews the mechanism of CO2 hydrogenation over Ni, Ru, and Cu, and the effect of catalyst properties and operating conditions on reaction kinetics. Most studies have reported the presence of CO and formate species on Ni-, Ru-, and Cu-based catalysts, where subsequent conversion of these species depends on the type of catalyst and the physicochemical properties of the catalyst support. Methane is the major product that forms during CO2 hydrogenation over Ni and Ru catalysts, while methanol and CO are mainly produced on Cu catalysts. A different approach for catalyst formulations and/or process development is required where long chain hydrocarbons are desired.

Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts

Abstract: ConspectusRecyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles—some without homogeneous analogues—for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity.Ongoing efforts in our laboratories are aimed to address the above challenge by heterogenizing homogeneous...

One-pot sol-gel synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon

Abstract: A single pot sol-gel method was adopted for the synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon for the first time. The catalysts were successfully synthesized via a facile sol-gel route without the assistance of any surfactants. The as-synthesized catalysts were completely characterized for their structural, textural and redox properties using several analytical techniques. The X-Ray diffraction analysis confirmed the formation of NiMgO solid solution and magnesioferrites as the active phases in the fresh catalysts. The inter-aggregation of nanoparticles in the catalyst generated pores, and a mesoporous texture resulted. The hydrogen chemisorption analysis indicated that the NiMgO solid solution was very difficult to reduce compared to the magnesioferrites. The thermocatalytic decomposition of methane at 700 °C, 800 °C and 900 °C fully validated their enhanced catalytic activity and stability for the reaction. The initial hydrogen yield and total carbon yield were found to be significantly increased, when the reaction temperature was increased. However, the highest catalytic performance was shown by the Fe/MgO catalyst. Moreover, no catalyst deactivation was observed for both of the catalysts for a period of 360 min of time on stream. This could be ascribed to their enhanced catalytic stability due to the presence of metal nanoparticles dispersed on the surface of the support, with proper metal-support interaction rather than their specific surface area. Multiwalled carbon nanotubes with metal encapsulated carbon particles and few layered graphene sheets were deposited over Ni/MgO and Fe/MgO catalysts, respectively. The studies of the effect of reaction temperature on the crystalline properties of the deposited nanocarbon indicated that the crystallinity and graphitization degree were increased with increasing reaction temperatures.

Enhancing CO2 electrolysis to formate on facilely synthesized Bi catalysts at low overpotential

Abstract: The electrochemical reduction of CO 2 to fuels and chemicals powered by renewable electricity has been regarded as a promising pathway, which can mitigate the greenhouse effect and energy crisis. However, the development of catalyst with high activity, selectivity, and good stability is still the bottleneck to accomplish this goal. In this communication, we report the promising performance of a micro-structured Bi catalyst which directly converts CO 2 to fuels at room temperature and ambient pressure. The Bi catalyst is designed by a simple and facile aqueous chemical reduction strategy, which readily scales up. The Bi 45 catalyst exhibits a superior catalytic activity for CO 2 conversion to formate, achieving a high Faradic efficiency of 90% at applied potential −1.45 V vs. SCE. The overpotential for the Bi 45 /GDE electrode is only 600 mV, a new record to all reported Bi catalysts in the literature. Particularly, the catalyst proves to be robust without any obvious degradation over 20 h of continuous electrolysis at −1.45 V vs. SCE. The notable activity achieved here is ascribed to the special micro-structure of the Bi catalyst, which may afford more active sites, as indicated by comparison to the structure of commercial Bi.