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Perisanu S.,Polytechnic University of Bucharest | Contineanu I.,Institute of Physical Chemistry of the Romanian Academy | Neacsu A.,Institute of Physical Chemistry of the Romanian Academy | Rath N.P.,University of Missouri-St. Louis | And 3 more authors.
Structural Chemistry | Year: 2013

The crystalline and gas phase enthalpy of formation of 5-cyano-7H-dibenzo- [a,c]-cyclohepten-6-amine (1) (142.0 ± 11.6 and 264 ± 20 kJ mol-1, respectively) are reported. The sublimation enthalpy at T = 298.15 K for this compound was evaluated by combining the fusion enthalpy from DSC measurements adjusted to 298 K with estimated vaporization enthalpy. The experimental enthalpy of formation is discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory and by means of group additivity. The crystal structure of this compound was determined by X-ray crystallography and shown to exist entirely in the cyanoenamine form 1, i.e. not the tautomeric α-cyanoimine 2. © 2013 Springer Science+Business Media New York.


Magureanu M.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Piroi D.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Mandache N.B.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Parvulescu V.I.,University of Bucharest | And 6 more authors.
Applied Catalysis B: Environmental | Year: 2011

Silver colloids have been prepared by reducing AgNO3 in aqueous solution and embeded in alumina following a sol-gel procedure in the presence of Pluronic 84 ((EO)19(PO)39(EO)19), as surfactant. Plasma-catalytic experiments aimed at the mineralization of toluene showed that the selectivity to CO2 was significantly increased in the presence of Ag catalysts compared with results obtained using the plasma alone. In-situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for mineralization reactions. It is noticeable that when ozone is chemisorbed on embedded Ag colloidal catalysts no change in the silver oxidation state or size is found. The population of the chemisorbed species is higher at lower temperatures, where the non-selective decomposition of ozone is smaller. The catalysts exhibit high stability, preserving the structural and textural properties after the catalytic tests, that is indeed very important in the presence of ozone. © 2011 Elsevier B.V.


Marinescu G.,Institute of Physical Chemistry of the Romanian Academy | Marinescu G.,University of Bucharest | Marin G.,University of Bucharest | Madalan A.M.,University of Bucharest | And 3 more authors.
Crystal Growth and Design | Year: 2010

The self-assembly processes between binuclear [Zn2] and [Cu 2] complex cations and exo-bidentate ligands [trans-4,4'-azo-pyridine (azpy), 4,4'-bipyridine (4,4'-bipy), 1,2-bis(4-pyridyl)ethane (bpeta), 1,3-bis(4-pyridyl)propane (bpp)] generate two types of complexes: tetranuclear species with a rectangular topology and one-dimensional (1-D) coordination polymers: [{L2(μ-OH)Cu2}(μ-azpy)2{Cu 2(μ-OH)L2}][{L2(μ-OH)Cu 2(H2O)}(μ-azpy)2{(H2O)Cu 2(μ-OH)L2}](ClO4)8 (1); [{L 1Cu2(H2O)2}(μ-azpy) 2{Cu2L1(H2O)2}](ClO 4)4•(azpy)•2H2O (2); 1 ∞[{Cu2(μ-OH)L3}(μ-bpp)] (ClO4)2 (3); 1 ∞[{L 3Zn2(μ-OH)}(μ-4,4'-bipy)](ClO4) 2•2H2O (4); 1 ∞[{L 3Zn2(μ-OH)}(μ-bpeta)](ClO4)2 (5a); 1 ∞[{L3Zn2(μ-OH)} (μ-bpeta)](ClO4)2•THF (5b); 1 ∞[{L2Zn2(μ-OH)}(μ-4,4'- bipy)2](ClO4)2•2H2O (6) (H 2Ln are compartmental Schiff-base ligands resulting from condensation reactions between 2,6-diformyl-p-cresol with, respectively, 1,3-diamino-propane, 2-aminoethyl-pyridine, and N,N-dimethyl-ethylenediamine). The zinc complexes exhibit luminescence properties. © 2010 American Chemical Society.


Marinescu G.,Institute of Physical Chemistry of the Romanian Academy | Marinescu G.,University of Bucharest | Andruh M.,University of Bucharest | Lloret F.,Departament Of Quimica Inorganica Institute Ciencia Molecular Icmol | Julve M.,Departament Of Quimica Inorganica Institute Ciencia Molecular Icmol
Coordination Chemistry Reviews | Year: 2011

The mononuclear oxalato-containing chromium(III) complexes of general formula [Cr(AA)(C2O4)2]- (AA=α-diimine type ligand) are able to produce a large variety of heterometallic complexes by acting as ligands towards either fully solvated metal ions or preformed cationic complexes with available coordination sites. This review focuses on the structural diversity of the polynuclear complexes (oligonuclear and coordination polymers) which are generated by the bis(oxalato)chromate(III) species, with a special emphasis to their magnetic properties. © 2010 Elsevier B.V.


Parvulescu V.I.,University of Bucharest | Cojocaru B.,University of Bucharest | Parvulescu V.,Institute of Physical Chemistry of the Romanian Academy | Richards R.,Colorado School of Mines | And 5 more authors.
Journal of Catalysis | Year: 2010

Silver colloids prepared by reducing AgNO3 in aqueous solution with sodium citrate were embedded in alumina following two different preparation procedures resulting in samples containing 3 and 5 wt.% silver. Characterization of these materials using TEM, XPS, XAES, CP/MAS NMR, XRD, and adsorption-desorption isotherms of nitrogen showed that embedding the pre-prepared silver colloids into the alumina via the sol-gel procedure preserved the particle size of silver. However, as XAES demonstrates, the catalysts prepared in a sol-gel with a lower amount of water led to embedded colloids with a higher population of Ag+ species. The catalytic behaviors of the resultant catalysts were well correlated with the concentration of these species. Thus, the active silver species of the catalysts containing more Ag+ species selectively converts NO to N2. However, subsequent thermal aging leads to an enhancement of the conversion of NO parallel to slight alteration of the selectivity with the appearance of low amounts of N2O despite an increase of Ag+ species. Accordingly, an optimal surface Ag0/Ag+ ratio is probably needed, independently of the size of silver particles. It was found that this optimal ratio strongly depends on the operating conditions during the synthesis route. © 2010 Elsevier Inc.


Papa F.,Institute of Physical Chemistry of the Romanian Academy | Balint I.,Institute of Physical Chemistry of the Romanian Academy | Negrila C.,National Institute of Materials Physics Bucharest | Olaru E.-A.,University of Bucharest | And 2 more authors.
Industrial and Engineering Chemistry Research | Year: 2014

Pd-Cu nanoparticles were synthesized by the alkaline polyol method and further supported on alumina or titania. The nanoparticles show a crystalline Pd core and a shell rich in amorphous copper as was put in evidence by complex characterization methods (X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and CO chemisorption). The performances of as-prepared catalysts in the water phase reduction of nitrate were assessed in comparison with catalysts obtained by impregnation. Supported nanoparticle catalysts show a high activity in the reduction of nitrates, better than the impregnated catalysts. The importance of the support choice was discussed. The catalyst based on Pd-Cu nanoparticles supported on titania (PCT-np) is the most active, selective, and stable among those investigated. Also, the influence of pH conditions on the PCT-np catalyst performances was emphasized. © 2014 American Chemical Society.


Papa F.,Institute of Physical Chemistry of the Romanian Academy | Negrila C.,National Institute of Materials Physics Bucharest | Miyazaki A.,Japan Women's University | Balint I.,Institute of Physical Chemistry of the Romanian Academy
Journal of Nanoparticle Research | Year: 2011

Well-dispersed, uniform monometallic Pt and bimetallic Pt-Cu, and Pt-Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core-shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results. © 2011 Springer Science+Business Media B.V.


Balint I.,Institute of Physical Chemistry of the Romanian Academy | Miyazaki A.,Japan Women's University | Gingasu D.,Institute of Physical Chemistry of the Romanian Academy | Papa F.,Institute of Physical Chemistry of the Romanian Academy
Reaction Kinetics, Mechanisms and Catalysis | Year: 2012

This article focuses on the catalytic behavior of MO-Sm 2O 3 (M = Zn, Mg, Ca, Sr) mixed oxides. The obtained results could be interpreted in terms of solid acid-base catalysis. The mixed oxides were prepared starting from the tartarate complexes of the constituent metals. The concentration as well as the evolution of surface carbonate species with the nature of MO and reaction temperature were analyzed by XRD and TPD methods. The amount of surface basic sites responsible for the formation of C 2 +was determined by measuring the amount of evolved CO 2 in the 300-800 °C temperature range. The catalytic behavior of the investigated mixed oxides was expressed in terms of methane yield to C 2 + and the concentration of CO 2 in reaction mixture. The conclusion is that C 2 + is formed on the basic sites whereas the acidic sites are responsible for nonselective oxidation of methane to CO 2. © Akadémiai Kiadó, Budapest, Hungary 2011.


Miyazaki A.,Japan Women's University | Numata M.,Japan Women's University | Etou M.,Fukuoka University | Yonezu K.,Fukuoka University | And 2 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2013

27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to investigate the effect of Zn2+ ion adsorption on Al(OH)3 gel. While as-prepared Al(OH)3 gel exhibits a single peak around 5ppm, the same gel with adsorbed Zn2+ has new peaks around 15 and 60ppm. These peaks correspond to AlO6 octahedral species with adsorbed Zn2+ and AlO4 tetrahedral species, respectively. In order to assess the mechanism for the formation of AlO4 tetrahedral species, hydroxide coprecipitates of Al3+ and Zn2+ were prepared and the chemical states of Al in the solids were observed by 27Al MAS NMR. The coprecipitates were found to have the AlO4 tetrahedral structure, except for those with high Zn/Al ratios. From these results, it can be assumed that adsorption of Zn2+ onto Al(OH)3 gel induces Al3+ dissolution followed by the coprecipitation of Al3+ with Zn2+ to form AlO4 tetrahedral structures on the surface of Al(OH)3 gel. © 2012 Elsevier B.V.


Miyazaki A.,Japan Women's University | Matsuda K.,Japan Women's University | Papa F.,Institute of Physical Chemistry of the Romanian Academy | Scurtu M.,Institute of Physical Chemistry of the Romanian Academy | And 3 more authors.
Catalysis Science and Technology | Year: 2015

Well-dispersed Pt-Cu nanoparticles with two average sizes were synthesized: small (≈1.6 nm) and large (≈4.8 nm), respectively. The effects of size and support on the catalytic behavior of the nanoparticles for denitration reaction were analyzed. Both the unsupported and alumina-supported nanoparticles of smaller average size (1.6 nm) were very active, completely converting NO3 - and NO2 - (an intermediate reaction product) to N2 and NH4 +. They were also more selective of N2 compared to the larger particles. The effects of particle size and alumina support on the denitration rate constants were analyzed in detail. The kinetic investigation indicates that the catalytic behavior is strongly related to the size of Pt-Cu nanoparticles as well as to the metal-support interaction. Generally, the larger nanoparticles proved to be less active, but on the other hand, they are less influenced by the support than the smaller ones. The metal-support interaction for bimetallic nanoparticles with smaller average size proved to be a key factor both for nitrate and nitrite reduction. Consideration of the reaction mechanism is made in light of the experimental results. © The Royal Society of Chemistry 2015.

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