The design of active and durable catalysts for the H
O/O
interconversion is one of the major challenges of electrocatalysis for renewable energy. The oxygen evolution reaction (OER) is catalyzed by ...SrRuO
with low potentials (ca. 1.35 V
), but the catalyst's durability is insufficient. Here we show that Na doping enhances both activity and durability in acid media. DFT reveals that whereas SrRuO
binds reaction intermediates too strongly, Na doping of ~0.125 leads to nearly optimal OER activity. Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO
octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites.
Ru size matters: This work investigates the catalytic consequences of Ru cluster size (4–23
nm) in the Fischer–Tropsch Synthesis. This reaction is structure sensitive when Ru
<
10
nm: turnover ...frequency of CO consumption increases as Ru size increases from 4 to 10
nm, reaching a constant value for larger clusters.
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► The performance of Ru catalysts for the synthesis of hydrocarbons is dominated by Ru particle size. ► Ru particles between 8–10
nm show the maximum rate for hydrocarbon production. ► Fischer–Tropsch Synthesis is a structure-sensitive reaction when Ru particles are smaller than 10
nm.
This work investigates the catalytic consequences of Ru cluster size in the Fischer–Tropsch Synthesis (FTS). Ru/Al
2O
3 catalysts with different metal particles size have been obtained by treating the solid in pure H
2 at increasing temperatures and times. Steady-state isotopic transient kinetic analysis (SSITKA) has been carried out at 523
K, 5.5
kPa CO, 55
kPa H
2, and 124.5
kPa inert in order to determine surface residence times and coverage of reversibly bonded CO and CH
x
intermediates as a function of Ru particle size (4–23
nm). We have found that FTS with Ru-based catalysts is a highly structure-sensitive reaction when Ru
<
10
nm. In this range, turnover frequency of CO consumption (TOF
CO) increases as the particle size increases, reaching a constant value for Ru particles larger than 10
nm. The lower intrinsic activity shown by Ru clusters <10
nm may be related to the stronger CO adsorption and concomitant partial blocking of active sites, as suggested by the decreased CO surface residence time as the Ru cluster size increases in the range below 10
nm.
Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO2. Recently, this process has attracted the ...attention of the industry due to the environmental benefits of CO2 elimination from the atmosphere and its lower operating costs with respect to the classical, two-step synthesis of DME from syngas (CO + H2). However, due to kinetics and thermodynamic limits, the direct use of CO2 as raw material for DME production requires the development of more effective catalysts. In this context, the objective of this review is to present the latest progress achieved in the synthesis of bifunctional/hybrid catalytic systems for the CO2-to-DME process. For catalyst design, this process is challenging because it should combine metal and acid functionalities in the same catalyst, in a correct ratio and with controlled interaction. The metal catalyst is needed for the activation and transformation of the stable CO2 molecules into methanol, whereas the acid catalyst is needed to dehydrate the methanol into DME. Recent developments in the catalyst design have been discussed and analyzed in this review, presenting the different strategies employed for the preparation of novel bifunctional catalysts (physical/mechanical mixing) and hybrid catalysts (co-precipitation, impregnation, etc.) with improved efficiency toward DME formation. Finally, an outline of future prospects for the research and development of efficient bi-functional/hybrid catalytic systems will be presented.
The effect of temperature and water/thiourea ratio on the growth, crystallinity and morphological characteristics of CdS nanostructures synthetized by a solvothermal method using ethylenediamine as ...solvent were studied. The temperature and water/thiourea ratio used in the synthesis determine the surface area, shape, length and degree of crystallinity of the CdS nanostructures obtained. Nanowires of high crystallinity and length were obtained when the solvothermal synthesis was performed at 190 °C, while nanorods with lower length and crystallinity were obtained as the solvothermal temperature decreased to 120 °C. The change in the water/thiourea ratio affects the crystallinity and length of the CdS nanostructures to a lesser extent than temperature. Nevertheless an increase in the water/thiourea ratio used during the solvothermal synthesis resulted in CdS nanorods with higher crystallinity, lower aspect ratio and lower specific surface area. Textural, structural and surface properties of the prepared CdS nanostructures were determined and related to the activity results in the production of hydrogen from aqueous solutions containing SO3(2-) + S(2-) under visible light.
The influence of nitrogen in the mechanism of ionic conduction has been studied in lithium phosphorus oxynitride glasses with composition xLi2O.(100−x)P2O5 (x=38–60mol%). A correlation between glass ...structure and ionic conductivity has been established for explaining the conduction mechanism. The change of glass structure during nitridation has been studied as a function of lithium and nitrogen contents. Raman spectra confirm the increase of P2O74− groups with increasing lithium and the presence of nitrogen, as also shown by X-Ray Photoelectron Spectroscopy. The O1s core-level XPS spectra allow determining the variation of the bridging (BO) to non-bridging (NBO) oxygen ratio, observing that its decrease is directly linked to an increase of ionic conductivity. The ionic conductivity of oxynitride glasses is higher than that of their parent phosphate glasses, although this increase also depends on the lithium content. Furthermore, it has been demonstrated that the influence of nitrogen is higher in glasses with smaller amount of lithium. These findings will contribute to the design of glasses with lower lithium contents and high ionic conductivity for their application as solid electrolytes in lithium rechargeable batteries.
► LiPON glasses with variable Li and N contents were prepared by ammonolysis. ► The lower the Li content the higher the increase of conductivity after nitridation. ► Nitrogen introduction produces a decrease of the BO/NBO ratio. ► The increase of the ionic conductivity by N depends on the variation of BO/NBO ratio.
Carbon nanotubes can be utilized in several ways to enhance the performance of silicon-based anodes. In the present work, thermally carbonized mesoporous silicon (TCPSi) microparticles and ...single-walled carbon nanotubes (CNTs) are conjugated to create a hybrid material that performs as the Li-ion battery anode better than the physical mixture of TCPSi and CNTs. It is found out that the way the conjugation is done has an essential role in the performance of the anode. The conjugation should be made between negatively charged TCPSi and positively charged CNTs. Based on the electrochemical experiments it is concluded that the positive charges, i.e., excess amine groups of the hybrid material interfere with the diffusion of the lithium cations and thus they should be removed from the anode. Through the saturation of the excess positive amine groups on the CNTs with succinic anhydride, the performance of the hybrid material is even further enhanced.
Density functional theory (DFT) studies of the interaction between graphene sheets and nitrile oxides have proved the feasibility of the reaction through 1,3‐dipolar cycloaddition. The viability of ...the approach has been also confirmed experimentally through the cycloaddition of few‐layer exfoliated graphene and nitrile oxides containing functional organic groups with different electronic nature. The cycloaddition reaction has been successfully achieved in one‐pot from the corresponding oximes under microwave (MW) irradiation. The successful formation of the isoxazoline ring has been confirmed by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X‐ray photoelectron spectroscopy (XPS).
Functionalizing graphene: The feasibility of the 1,3‐dipolar cycloaddition reaction of oximes to the surface of few‐layer exfoliated graphene is demonstrated by theoretical calculations and experimentally.
Delamination of Layered Covalent Organic Frameworks Berlanga, Isadora; Ruiz-González, Maria Luisa; González-Calbet, José María ...
Small (Weinheim an der Bergstrasse, Germany),
May 9, 2011, Letnik:
7, Številka:
9
Journal Article
Recenzirano
The isolation of nanostructures consisting of 10–25 layers of a covalent organic framework is confirmed by AFM carried out on several surfaces. This is achieved by means of selective ultrasound ...exfoliation on the bulk layered material. TEM demonstrates the porous nature of the free‐standing layers on a carbon gird. The chemical composition of this novel 2D polymer is determined by infrared, X‐ray photoelectron, and electron‐energy‐loss spectroscopy.
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The non-enzymatic determination of glucose is a current trend in analytical chemistry. Copper-based nanomaterials are being widely employed for the fabrication of electrochemical ...analytical devices for glucose monitoring. In this work, copper-modified titanium phoshate nanoparticles (CuTiPNPs) were synthesized for the first time. Interestingly, CuTiPNPs show an electrocatalytic effect towards the oxidation of glucose. These nanoparticles were characterized by different techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy, voltammetry and electrochemical impedance spectroscopy. Important information on the structural, morphological, surface and electrochemical properties was obtained. A mechanism involving a Cu(III) species stabilized by phosphate groups of the nanoparticles is proposed for the oxidation of glucose. The analytical performance of 8-channel screen-printed electrodes modified with CuTiPNPs for glucose determination was evaluated. A wide linear range from 25μM to 2mM and a limit of detection of 7μM was obtained. The good analytical figures of merit and the good selectivity towards glucose led to the versatile and accurate non-enzymatic glucose determination in real samples such as honey and plasma.
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