Integrated Ni/Nb2O5 nanocatalytic agent dose for improving the hydrogenation/dehydrogenation kinetics of reacted ball milled MgH2 powders

Reactive ball milling (RBM) technique was employed to synthesize ultrafine powders of MgH₂, using high energy ball mill operated at room temperature under 50 bar of a hydrogen gas atmosphere. The MgH₂ powders obtained after 200 h of continuous RBM time composed of β and γ phases. The powders possessed nanocrystalline characteristics with an average grain of about 10 nm in diameter. The time required for complete hydrogen absorption and desorption measured at 250 °C was 500 s and 2500 s, respectively. In order to improve the hydrogenation/dehydrogenation kinetics of as synthesized MgH₂ powders, three different types of nanocatalysts (metallic Ni, Nb₂O₅ and (Ni)_x/(Nb₂O₅)_y) were utilized with different weight percentages and independently ball milled with the MgH₂ powders for 50 h under 50 bar of a hydrogen gas atmosphere. The results showed that the prepared nanocomposite MgH₂/5Ni/5Nb₂O₅ powders possessed superior hydrogenation/dehydrogenation characteristics, indexed by low values of activation energy for β-phase (68 kJ/mol) and γ-phase (74 kJ/mol). This nanocomposite system showed excellent hydrogenation/dehydrogenization behavior, indexed by the short time required to uptake (41 s) and release (121 s) of 5 wt% H₂ at 250 °C. At this temperature the synthesized nanocomposite powders possessed excellent absorption/desorption cyclability of 180 complete cycles. No serious degradation on the hydrogen storage capacity could be detected and the system exhibited nearly constant absorption and desorption values of +5.46 and −5.46 wt% H₂, respectively.     

Characterization of cobalt oxide nanocatalysts prepared by microemulsion with different surfactants, reduction by hydrazine and mechanochemical method

Cobalt oxide (Co₃O₄) nanoparticles were prepared by different techniques (i) by microemulsion with different surfactants, (ii) by reduction as nanometal with hydrazine hydrates and (iii) by thermal treatment of precursor obtained from mechanochemical reaction of Co(NO₃)·H₂O with NH₄HCO₃. The products were calcined at 400 °C to give crystalline Co₃O₄. The obtained different samples of Co₃O₄ were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) from which the particle size was calculated. The results revealed that all samples obtained from different methods were nanosized particles.     

Preparation of CeO2/ZnO nanostructured microspheres and their catalytic properties

CeO₂/ZnO nanostructured microspheres with an average diameter of about 3.8 μm were synthesized by a solid-stabilized emulsion route. The CeO₂/ZnO nanostructured microspheres were characterized with SEM, XRD, CO₂-TPD, BET measurement and size analysis. Based on the oxidative coupling reaction of methane with carbon dioxide as an oxidant, the catalytic performance of the CeO₂/ZnO nanostructured microspheres was evaluated and compared with that of the CeO₂/ZnO nanoparticles. The results showed that the surfaces of the CeO₂/ZnO nanostructured microspheres consisted of petal-like structures with a petal thickness of about 90 nm and a petal depth of 0.4 μm to 0.9 μm. Using CeO₂/ZnO nanostructured microspheres as catalysts for the oxidative coupling of methane with carbon dioxide, the conversion of methane corresponded with that using the CeO₂/ZnO nanoparticles, while the CeO₂/ZnO nanostructured microspheres had much longer operating life.     

纳米催化剂在生物柴油合成中的应用

生物柴油作为一种可再生的绿色能源,是化石燃料理想的替代品.该文聚焦于纳米催化剂在生物柴油合成中的应用,对常见的纳米催化剂的设计、制备、物化性质、催化行为及重复使用性等方面进行了综述.提出了纳米催化剂在生物柴油合成中所面临的问题并展望其应用前景.     

Thin layer vs. nanoparticles: Effect of SnO2 addition to PtRhNi nanoframes for ethanol oxidation reaction

When designing catalysts for direct ethanol fuel cell applications (DEFC), four main parameters must be considered: shape, structure, size, and chemical composition. According to this knowledge, it is assumed that polyhedral hollow Pt-based nanoframes, with the addition of Rh and SnO₂ with a size below 50 nm, could be a promising nanocatalysts for the anode of DEFC. In this work, two different PtRhNi/SnO₂ nanoframes-based catalysts are obtained. First consists of PtRhNi nanoframes covered with small, about 3 nm, SnO₂ nanoparticles (PtRhNi/SnO₂ NPs); and second is the PtRhNi nanoframes covered with a thin and incomplete SnO₂ layer (PtRhNi/SnO₂ TL). Both nanocatalysts were tested toward ethanol oxidation reaction (EOR) and show higher activity in comparison to PtRhNi nanoframes without SnO₂ (PtRhNi NFs) addition and commercially used Pt nanoparticles. Especially, the electrochemical durability and stability of obtained nanocatalysts were tested. It was shown that both PtRhNi/SnO₂ nanoframes-based catalysts develop similar mass and specific activity, as well as nearly the same onset potential, but their stability is significantly different. It turns out, that catalyst based on PtRhNi nanoframes covered with a thin SnO₂ layer is susceptible to degradation, while the catalyst consisting of PtRhNi nanoframes covered with SnO₂ nanoparticles is much more durable and could be used as an efficient catalyst toward EOR.     

Electrophoretically fabricated nickel/nickel oxides as cost effective nanocatalysts for the oxygen reduction reaction in air-cathode microbial fuel cell

The high cost and limited availability of cathode catalyst materials (most commonly Pt) prevent the large-scale practical application of microbial fuel cells (MFCs). In this study, unique Pt group metal-free (PGM-free) nanocatalysts were fabricated using a simple and cost-effective technique called electrophoretic deposition (EPD) to create a high catalytic oxygen reduction reaction rate (ORR) on the cathode surface of MFCs. Among the tested PGM-free catalysts (Ni, Co, and Cd-based), a maximum power density of 1630.7 mW m⁻² was achieved based on nickel nanoparticles. This value was 400% greater than that obtained using a commercial Pt catalyst under the same conditions. This result was due to the uniform deposition of a thin layer of Ni/NiO_x nanoparticles on the cathode, which improved electrical conductivity, catalytic activity, and long-term stability while reducing electron transfer resistance. The fabricated PGM-free catalysts significantly improved MFC performance and accelerated ORR induced by the novel layered morphology of metal/metal oxide nanoparticles.     

NiPdPt trimetallic nanoparticles as efficient electrocatalysts towards the oxygen reduction reaction

In this article, the synthesis and characterization of NiPdPt (60:20:20 wt. %) nanoparticles supported on Vulcan carbon are analyzed towards the oxygen reduction reaction (ORR) in acid medium. We report a novel trimetallic nanocatalyst produced by a synthetic chemical route by reacting chemical reagents in oleylamine and oleic acid. The physical characterization of the synthesized nanoparticles was performed by X-ray diffraction (XRD), energy disperse X-ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM). The presence of Ni, Pd, and Pt in the nanoparticles was confirmed by EDS and XRD. From STEM micrographs, a size distribution of nanoparticles in a range of 30–52 nm was obtained. In the electrocatalyst research, cyclic voltammetry (CV), CO-stripping, and rotating disk electrode (RDE) were employed for electrochemical evaluation of the synthesized nanoparticles in acid medium. The NiPdPt/C nanocatalyst showed superior mass and specific activity compared to the commercial Pt/C towards the ORR in acid medium.     

Copper zinc oxide nanocatalysts grown on cordierite substrate for hydrogen production using methanol steam reforming

Hydrogen production from methanol rather than the traditional source, methane, is considered to be advantageous in ease of transportation and storage. However, the current copper-based catalysts utilized in methanol steam reforming are associated with challenges of sintering at high temperature and production of CO which could poison fuel cells. In addressing these challenges, ZnO nanorods were grown hydrothermally on the surface of cordierite and impregnated with Cu to produce catalysts for methanol steam reforming. The catalysts were characterized using SEM, XRD, FTIR, XPS, BET and Raman Spectroscopy. A fixed-bed reactor was used for testing the catalysts while the reaction products were characterized using a GC fitted with FID and TCD. The effects of temperature, methanol concentration and particle size of catalysts on methanol steam reforming were investigated. The experiments were carried out between 180 and 350 °C. CO selectivity of 0% was observed for temperatures between 180 and 230 °C for 0.8 MeOH:1H₂O with an average H₂ selectivity of 98% for that temperature range. XPS showed that the catalyst was relatively unchanged after reaction while Raman spectroscopy revealed coke formation on the catalyst surface for reactions carried out above 300 °C. This shows that the catalyst is active and selective for the reaction.     

Metal Nanocrystals Embedded within Polymeric Nanostructures: Effect of Polymer-Metal Compound Interactions

pH-responsive PDEAEMA-b-PHEGMA amphiphilic block copolymers and random polymer networks have been used as matrices for the incorporation of metal species and the nucleation and growth of metal nanoparticles with sizes in the range of a few nanometers. The polymer characteristics and polymer-metal interactions upon metal incorporation and after metal reduction were investigated. Two different synthetic procedures were followed for the preparation of Pt nanoparticles within the block copolymers; addition of the metal precursor in a molecular copolymer solution at low pH led to a polymer-metal charge neutralization process and the formation of micelles with compact non-hydrated cores, while the incorporation of H₂PtCl₆ in a micellar copolymer solution at high pH led to polymer aggregation. The impregnation of K₂PtCl₆ in a micellar copolymer solution at high pH was unsuccessful suggesting the lack of coordination of the neutral amine groups to the metal precursor. The effect of the metal precursor impregnation and the metal nanoparticle formation on the degree of swelling of random networks carrying different functionalities was also examined and the metal content of the hybrid materials was assessed. The equilibrium degrees of swelling of the networks were determined by two opposing effects: the degree of ionization, which caused the network to swell, and the polymer-metal complexation, which increased the effective cross-link density and caused the network to shrink. The metal content of the network was dictated by the polymer-metal interactions and the degree of swelling of the network in the solvent medium. These hybrid materials are proposed for use as advanced catalysts in the synthesis of high-value cosmetics and pharmaceuticals.     

Hydrogen generation over Ni@Pd NCs through an active H-exchange from formic acid-water system

The use of Formic acid as an alternative to fossil fuels is promising, both from economical and ecological standpoints, and has received great of attention owing to its inherently superiority in recent decades. Nevertheless, efficient and low-cost solid catalyst for formic acid dehydrogenation at room temperature still constitutes a biggish challenge. Moreover, comparing to increase the catalytic performance of catalysts, very little attention payed to the kinetic mechanism of dehydrogenation reaction because of the lack of effective characterization artifice. Here, the as-prepared Ni@Pd nanoparticles by a sequential reduction process can be useful catalyst for formic acid decomposition at room temperature without a promoter. Thanks to the effective catalyst and isotope distribution technique, preliminary mechanistic results firstly reveal that hydrogen is obtained via a H-atom recombination on isolated sites after the proton exchange randomly between activated H and solvent.