121,981 research outputs found
Mechanistic study of hydrazine decomposition on Ir(111)
No full textHydrogen transport and storage technology remain one of the critical challenges of the hydrogen economy. Hydrazine (N2H4) is a carbon-free hydrogen carrier which has been widely used as fuel in the field of space exploration. We have combined experiments and computer simulations in order to gain a better understanding of the N2H4 decomposition on Ir catalyst, the most efficient catalyst for hydrazine decomposition up to date. We have identified metallic Ir rather than IrO2 as the active phase for hydrazine decomposition and carried out density functional theory (DFT) calculations to systematically investigate the changes in the electronic structure along with the catalytic decomposition mechanisms. Three catalytic mechanisms to hydrazine decomposition over Ir(111) have been found: (i) intramolecular reaction between hydrazine molecules, (ii) intramolecular reaction between co-adsorbed amino groups, and (iii) hydrazine dehydrogenation assisted by co-adsorbed amino groups. These mechanisms follow five different pathways for which transition states and intermediates have been identified. The results show that hydrazine decomposition on Ir(111) starts preferentially with an initial N-N bond scission followed by hydrazine dehydrogenation assisted by the amino group produced, eventually leading to ammonia and nitrogen production. The preference for N-N scission mechanisms was rationalized by analyzing the electronic structure. This analysis showed that upon hydrazine adsorption, the π bond between nitrogen atoms becomes weaker
Gold based bimetallic catalysts for liquid phase application
No full textThe liquid phase oxidation of D-Sorbitol has been carried out in water using oxygen as the oxidant in the presence of gold based catalyst. Au/C, Pt/C and Pd/C monometallic systems were compared to bimetallic Au/Pd and Au/Pt on carbon. A strong synergistic effect was observed producing a significant increase of reaction rate. Moreover, the addition of gold to Pd or Pt catalyst produced a system more resistant to oxygen poisoning allowing it to work also under a moderate pressure. The effect of varying the molar ratio of the metals has also been studied
Catalytic transformation of renewables (Olefin, bio‐sourced, et al.)
No full textThe objective of this Special Issue is to provide new diverse contributions that can
demonstrate recent applications in biomass transformation using heterogeneous catalysts.
In recent decades, a wide variety of biomass-derived chemicals have emerged as key platform chemicals for the production of fine chemicals and liquid fuels using heterogeneous
catalysts as the preferred option for most of the developed and proposed catalytic processes.
A range of heterogeneous catalysts have been evaluated for effective biomass conversion,
such as supported metal nanoparticles, mixed metal oxides and zeolites, where the control
of particle size, porosity, acid-basic and redox properties is crucial for providing active,
stable and selective heterogeneous catalysts. Moreover, the crucial role of the solvent,
choice of reactor design and final chemical processes for controlling activity, selectivity and
deactivation phenomena has been demonstrate
Optimization of the Zr-loading on siliceous support catalysts leads to a suitable Lewis/Bronsted acid sites ratio to produce high yields to gamma-valerolactone from furfural in one-pot
No full textThe study for the production of gamma-valerolactone from furfural in one-pot has been carried out using ZrO2 supported on silica spheres. The catalysts synthesized were characterized by XRD, UV-vis, HR-TEM, N-2 adsorption, IR, pyridine adsorption-IR and NH3-TPD in order to determine their physicochemical characteristics. Both, Lewis and Bronsted acid sites are necessary to produce gamma-valerolactone from furfural, because they are involved in different steps of the reaction. Accordingly, a reaction mechanism has been proposed. Lewis acid sites of ZrO2 interacting with the -OH surface groups of the siliceous spheres can generate Bronsted acid sites in the supported Zr catalysts, which are absent in both pure ZrO2 and the silica spheres. Then, by controlling the amount of Zr in the supported catalysts, the relative amount of Lewis and Bronsted acid sites can be optimized to obtain the highest yields to gamma-valerolactone. The Zr-loading of the optimal supported catalyst was ca. 7 wt% Zr, which reached a gamma-valerolactone yield of 72.4 % after 8 h at 180 C using 2-propanol as a solvent and hydrogen donor
Hydrous hydrazine decomposition for hydrogen production using of ir/ceo2: Effect of reaction parameters on the activity
No full textIn the present work, an Ir/CeO2 catalyst was prepared by the deposition–precipitation method and tested in the decomposition of hydrazine hydrate to hydrogen, which is very important in the development of hydrogen storage materials for fuel cells. The catalyst was characterised using different techniques, i.e., X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with X‐ray detector (EDX) and inductively coupled plasma—mass spectroscopy (ICP‐MS). The effect of reaction conditions on the activity and selectivity of the material was evaluated in this study, modifying parameters such as temperature, the mass of the catalyst, stirring speed and concentration of base in order to find the optimal conditions of reaction, which allow performing the test in a kinetically limited regime
Catalytic formation of C(sp3)-F bonds via decarboxylative fluorination with mechanochemically-prepared Ag2O/TiO2 heterogeneous catalysts
No full textMechanochemically-prepared, Ag2O-containing solid materials, are shown to be efficient heterogeneous catalysts for the synthesis of C(sp3)-F bonds via decarboxylative fluorination. Five catalytic cycles without loss of intrinsic activity could be performed with the optimal catalyst, composed of 1 wt% Ag2O supported on TiO2 (P25), despite the challenging conditions. The catalyst is easily prepared from the corresponding oxides in 20 minutes by simple mechanical mixing methods. In addition to ease of separation and re-use, the turnover numbers obtained over the solid catalyst are over one order of magnitude higher than those obtained with the state-of-the-art homogeneous catalyst, AgNO3, under otherwise identical conditions. To the best of our knowledge, this represents the first true heterogeneous catalyst for the selective formation of C(sp3)-F bonds with electrophilic fluorine donors, representing a major breakthrough in the field of catalytic fluorination
Supported Metal Nanoparticles with Tailored Catalytic Properties through Sol immobilisation: Applications for the Hydrogenation of Nitrophenols
No full textColloidal Pd nanoparticles, prepared at different temperatures and supported on TiO2 support via sol immobilisation were studied for their performance in the catalytic hydrogenation of nitrophenols. The physicochemical properties of the catalysts were characterised in depth using a range of techniques, including UV-vis spectroscopy, TEM, IR and XAFS. The dataset contains TEM micrographs, as well as Origin and Athena (XAFS) files relating to the catalyst characterisation. The catalytic performance data for the aforementioned hydrogenation reaction, including conversion profiles and first order kinetics, is also documented.</span
A Career in Catalysis: Laura Prati
No full textThis account celebrates the long and successful scientific career of Laura Prati, recalling her most important scientific achievements since the beginning of her work as a researcher in inorganic chemistry. Laura went through many aspects of liquid-phase heterogeneous catalysis, taking her first steps in the field of catalysts
synthesis, where she pursued the development of innovative strategies for preparing catalysts until laying the foundations of the colloidal synthesis of metal nanoparticles, with particular interest in gold. Her investigations in colloids for catalysis had a natural outcome on catalysts synthesis and optimization. In her career, she dealt with liquidphase oxidation reactions, with particular attention to biomass valorization processes. According to this, she could not help to deal
also with hydrogenation and hydrogenolysis reactions, to which she dedicated herself, especially in the more recent years. Her discoveries have influenced many researchers in the area of heterogeneous catalysis and design of materials
Metal-free Doped Carbons for Electroanalytical Sensors
No full textIn this chapter, a quick excursus of metal-free doped carbon materials for the modification of electrodes to be used in electroanalytical sensors has been made. After a brief introduction to the different methods available for modified electrode preparation, the most used carbonaceous materials doped with heteroatoms (B, N, O, P, S) have been considered: carbon paste and ordered carbons, glassy carbon, boron-doped diamond and amorphous carbon, carbon nanotubes, and graphene. The effect of the presence of metals, graphitic and amorphous carbon impurities, which is not completely avoidable when considering these materials, has also been discussed
Influence of hydro-soluble polymeric stabilizers in nano-catalysis: molecular weight effect
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