National Institute Of Materials Physics - Romania

Publications

163 articles found

111. Evidence of A-B site cooperation in the EuFeO3 perovskite from Eu-151 and Fe-57 Mossbauer spectroscopy, EXAFS, and toluene catalytic oxidation

Authors: Florea, M; Alifanti, M; Kuncser, V; Macovei, D; Apostol, N; Granger, P; Parvulescu, VI

Published: JUL 2014, JOURNAL OF CATALYSIS, 316, 140, DOI: 10.1016/j.jcat.2014.04.016

EuFeO3 perovskite was considered as a case study of the cooperative effects of the rare earth and transition metal elements in the total catalytic oxidation of aromatic hydrocarbons. For this purpose, a EuFeO3 perovskite was prepared using the citrate route. Extensive characterization was performed via ex situ and in situ methods. EXAFS revealed that oxygen vacancies are formed in the nearest neighborhood of Fe and next-nearest neighborhood of Eu. Combining Eu-151 and Fe-57 Mossbauer experiments also suggested local oxygen defects in the proximity of the Eu cations during the reaction, as well as cooperative electron delocalization effects between Eu and Fe. XPS has shown the +3 oxidation state of both Eu and Fe cations and the relatively strong ionicity of the Fe-O chemical bonds, as suggested by the weakened 2p(3/2) satellite in the Fe2p spectrum. A systematic change of this satellite with the A cation in AFeO(3) perovskites was also discussed. The thermal treatment of the catalyst at 623 K, in air or toluene, was accompanied by a partial reduction of Fe and a partial oxidation of Eu, respectively. The interaction between the two elements appeared to be influenced mainly by the temperature and only slightly by the sample environment during further treatments. Catalytic oxidation of toluene on this perovskite led only to the production of carbon dioxide and water with no side-product formation from partial oxidation reactions. All the characterization and catalytic results preferably agree with a Volkenstein mechanism. (C) 2014 Elsevier Inc. All rights reserved.

112. Comment on "High multi-photon visible upconversion emissions of Er3+ singly doped BiOCl microcrystals: A photon avalanche of Er3+ induced by 980 nm excitation" [Appl. Phys. Lett. 103, 231104 (2013)]

Authors: Tiseanu, C; Florea, M; Cojocaru, B

Published: JUN 9 2014, , DOI: 10.1063/1.4882167

113. Thermal behavior of several stable hydrazyl free radicals and of their parent hydrazines

Authors: Marinescu, M; Zalaru, C; Florea, M; Ionita, P

Published: APR 2014, , DOI: 10.1007/s10973-013-3448-x

114. Heavily impregnated ceria nanoparticles with europium oxide: spectroscopic evidences for homogenous solid solutions and intrinsic structure of Eu3+-oxygen environments

Authors: Avram, D; Rotaru, C; Cojocaru, B; Sanchez-Dominiguez, M; Florea, M; Tiseanu, C

Published: MAR 2014, , DOI: 10.1007/s10853-013-7904-6

115. Structural changes during toluene complete oxidation on supported EuFeO3 monitored by in situ Eu-151 and Fe-57 Mossbauer spectroscopy

Authors: Florea, M; Alifanti, M; Kuncser, V; Parvulescu, VI

Published: JUN 1 2013, CATALYSIS TODAY, 208, 59, DOI: 10.1016/j.cattod.2012.09.035

Pure EuFeO3 and ceria were prepared via a sol-gel citrate route and were calcined at 700 degrees C. Separately, a 20 wt% EuFeO3/CeO2 was prepared via incipient wetness impregnation of calcined ceria with citrate precursors and calcined in the same conditions. SBET, XRD, toluene chemisorption, toluene-TPD and in situ Eu-151 and Fe-57 Mossbauer investigations were performed. All characterization data indicate the formation of a well-dispersed EuFeO3 at the surface of CeO2. During the oxidation of toluene Eu-151 and Fe-57 Mossbauer spectroscopy suggested a cooperative effect of the cations. The catalysts were tested in total oxidation of toluene. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuFeO3. All structural changes during operation time were reversible. (C) 2012 Elsevier B.V. All rights reserved.

116. Postsynthetic Modification of a Metal-Organic Framework (MOF) Structure for Enantioselective Catalytic Epoxidation

Authors: Candu, N; Tudorache, M; Florea, M; Ilyes, E; Vasiliu, F; Mercioniu, I; Coman, SM; Haiduc, I; Andruh, M; Parvulescu, VI

Published: MAY 2013, CHEMPLUSCHEM, 78, 450, DOI: 10.1002/cplu.201300076

Postsynthetic modification of [Cu2(mand)2(hmt)] (mand=mandelic acid, hmt=hexamethylenetetramine) with a chiral, dimeric chromium(III)salen complex led to a robust structure. Characterization of this new material showed that it perfectly preserved the textural and structural properties of the parent metalorganic framework (MOF). Although epoxidation of trans-methyl cinnamate with hydrogen peroxide led to copper leaching of 23%, experiments performed with N-methylmorpholine-N-oxide indicated no leaching, even after 72h of exposure. The obtained chiral MOF is an effective catalyst for the enantioselective epoxidation of trans-methyl cinnamate and leads to (2R,3S)-phenylglycidate with a high enantiomeric excess at room temperature.

117. A Robust Metal-Organic Framework Constructed from Alkoxo-Bridged Binuclear Nodes and Hexamethylenetetramine Spacers: Crystal Structure and Sorption Studies

Authors: Ilyes, E; Florea, M; Madalan, AM; Haiduc, I; Parvulescu, VI; Andruh, M

Published: AUG 6 2012, , DOI: 10.1021/ic301139j

118. Spectroscopic Analysis of the Interstitial Anions in Some Layered Double Hydroxide Materials

Authors: Frunza, L; Gheorghe, N; Iova, F; Ganea, P; Neatu, F; Parvulescu, VI

Published: AUG 2011, REVISTA DE CHIMIE, 62, 772, DOI:

Layered double hydroxide materials with Zn2+ and Mg2+ as bivalent cations and Al3+ and Ga3+ as trivalent cations were studied. The anions to balance the positive charge of the network were carbonate and/or nitrate. The samples were prepared in laboratory and routinely characterized. Here the investigations by Fourier transform infrared spectra and thermogravimetric measurements are detailed. On the basis of calibration curves for carbonate and nitrate ions obtained from IR spectra of the corresponding salts, the sample analysis of the interlayer anions was performed quantitatively.

119. Benzylation of benzene with benzyl alcohol on zeolite catalysts

Authors: Candu, N; Florea, M; Coman, SM; Parvulescu, VI

Published: FEB 15 2011, , DOI: 10.1016/j.apcata.2010.11.044

120. Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)-Salen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester

Authors: Protesescu, L; Tudorache, M; Neatu, S; Grecu, MN; Kemnitz, E; Filip, P; Parvulescu, VI; Coman, SM

Published: FEB 3 2011, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 1122, DOI: 10.1021/jp106281z

A dimer chromium(III)-salen complex immobilized on modified silica is an effective catalyst for the epoxidation/epoxide ring-opening reaction of trans-methylcinnamate ester and gave significantly high ee in methyl (2R,3S)-2,3-dihydroxy-3-phenylpropionate. For the first time, it is shown that a donor ligand (e.g., Et3N) can be involved into the enantioselective mechanism of the product configuration. It is suggested that the additive is interacting with the reaction intermediate in a manner that prolongs its lifetime, thus affording a free rotation of the C-C single bond in this species and a selective collapse to the cis-epoxide product. In the presence of water, this epoxide led to methyl (2S,3R)-2,3-dihydroxy-3-phenylpropionate. Alternatively, the donor additives may give rise to a new chromium-based oxidant that effects epoxidation and its consecutive ring opening to diols via an unusual pathway.