12014-56-1Relevant articles and documents
Diehl, H.,Smith, G. F.
, p. 382 - 383 (1959)
Carnelley, T.,Walker, J.
, p. 59 - 101 (1888)
Hydrolysis of lanthanide dicarbides. Rates of reaction with water
McColm, I. J.,Quigley, T. A.,Bourne, D. R.
, p. 191 - 198 (1991)
The kinetics of the reaction between liquid water and nine lanthanide dicarbides and YC2 have been investigated by monitoring the gas evolved into a constant volume apparatus. The ratio of volume of gas-evolved to that predicted was found to be consistent at 0.51 for wholly trivalent dicarbides, but rose to 0.66 for the light lanthanides containing LnIV components. Only linear kinetics were observed with the linear reaction rate constant KL in the range 0.44 cm cm-2 min-1 for LuC2 to 6.9 cm cm-2 min-1 for CeC2. Over the limited temperature range 283-303.5 K it was possible to estimate activation energies for four of the dicarbides and the values ranged from 48.5 kj mol-1 for the heavy, hard carbides to 150 kJ mol-1 for the light, soft, LnIV-containing members. The variation of KL and E across the series is discussed in terms of M-C2 bond energies, 4f-band electron density and the hardness of these dicarbides.
Synthesis methods for Ce(CrO4)2 · xH 2O and crystal structures of K2CrSO7, (NH 4)2Cr2O7 and Na2Cr 2O7 · 2H2O
Casari, Barbara M.,Eriksson, Annika K.,Langer, Vratislav
, p. 771 - 777 (2007)
New and quick methods to synthesize Ce(CrO4)2 · 2H2O and Ce(CrO4)2 · H 2O, giving high yields, are described. The methods are based on exchange reactions by refluxing in water or on solid state reactions. The first crystal structure containing a chromatosulfato ion is presented. K 2CrSO7 belongs to space group P21/n with a = 7.4024(1), b = 7.3908(1), c = 12.9883(2) A?, β = 90.021(1)° and Z = 4. The CrSO72- ion, consisting of one chromate group sharing one oxygen atom with one sulfate group, has a pseudo syn-C2v conformation with eclipsed oxygen atoms. K2CrSO7 forms a three dimensional network of CrSO72- ions held together by the charge balancing potassium ions, with the general structural features common with dichromate-like structures. The redetermination of the structures of (NH4)2Cr2O7 (space group C2/c, with hydrogen atoms located) and Na2Cr2O7 · 2H2O (space group P21, with hydrogen atoms located and the absolute structure established) are reported.
Facile synthesis of ceria nanoparticles by precipitation route for UV blockers
Anupriya,Vivek,Subramanian
, p. 406 - 410 (2014)
Homogeneous ceria (CeO2) nano particles of approximately 4 nm have been successfully synthesized via a simple precipitation route by employing the mixed solvent method. X-ray diffraction analysis revealed the precipitate particles to be of highly crystalline nature with face centered cubic structure along (1 1 1) (2 0 0) (2 2 0) (3 1 1) (4 0 0) (3 3 1) (4 2 2) (5 1 1) planes. Cerium oxide nanoparticles exhibits enhanced specific surface area of about 139.116 m2/g. The mono-dispersed spherical shape morphology of approximately 4 nm particles was confirmed using TEM analysis and its chemical composition by SEM-EDS analysis. Surface morphology reveals the smooth surface with an average roughness of 14.9 nm with the help of AFM. Raman studies show a characteristic peak at 464 cm-1. The UV absorption edge was found at 314 nm i.e. In the Ultra Violet region suggesting that the material has a good absorption of UV light. Also, it shows an excellent transparency in the visible region.
Dipotassium tetrachromate(VI), K2Cr4O13
Casari, Barbara M.,Langer, Vratislav
, p. i117-i119 (2005)
The structure of dipotassium tetrachromium(VI) tridecaoxide, K 2Cr4O13, has been determined from single-crystal X-ray data collected at 173 (2) K on a racemically twinned crystal with monoclinic Pc space-group symmetry. The structure is composed of discrete [Cr4O13]2- zigzag chains held together by the charge-balancing potassium ions. The conformations adopted by the tetrachromate anion in alkali metal salts and Cr8O21 are different and can be divided into three categories.
New structure type among octahydrated rare-earth sulfates, β-Ce 2(SO4)3·8H2O, and a new Ce 2(SO4)3·4H2O polymorph
Casari, Barbara M.,Langer, Vratislav
, p. 1074 - 1081 (2007)
Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce2(SO4) 3·4H2O (I) and β-Ce2(SO 4)3·8H2O (II), both forming three-dimensional networks. Compound I crystallizes in the space group P2 1/n. There are two non-equivalent cerium atoms in the structure of I, one nine-and one ten-fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge-sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S-Oμ3-Ce2 bonding mode. Compound II constitutes a new structure type among the octahydrated rare-earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H2O)4(SO4)]nn+ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce2(SO4)3·5H 2O, Ce2(SO4)3·4H2O and Ce2(SO4)3, respectively. During the oxidative decomposition of the anhydrous form, Ce2(SO 4)3, into the final product CeO2, small amount of CeO(SO4) as an intermediate species was detected.
Catalysis on Ruthenium Clusters Supported on CeO2 or Ni-Doped CeO2: Adsorption Behavior of H2 and Ammonia Synthesis
Izumi, Yasuo,Iwata, Yasuhiro,Aika, Ken-ichi
, p. 9421 - 9428 (1996)
Catalysis on Ru clusters supported on CeO2 or Ni-doped CeO2 was investigated.Ru3(CO)12 was reacted with CeO2, followed by heating in vacuum at 673 (i) or 813 K (ii) and then in H2 at 588-1073 K (TH2).Activities of both catalysts had the TH2 dependence, which has a maximum at TH2 = 873 K for ammonia synthesis.The rates on i were faster than those on ii by a factor of 2.0-1.1 in the range of TH2 = 588-973 K.On a sample in which Ru3(CO)12 was supported on previously reduced Ni/CeO2 (in H2 at 773 K) iii, the highest synthesis rate was 1.5E-3 mol h-1 gcat-1 at TH2 = 588 K on iii.The activity order iii > i > ii can be understood in terms of two factors: (A) reduction extent of support and (B) number of active Ru sites.The two factors conflicted with each other when the treatment temperature in H2 increased.By heating the samples in H2 up to 873 K to satisfy factor A, the aggregation of Ru clusters for i or physical blocking of surface Ru sites by CeO2-x for ii occurred: factor B was not satisfied.The two factors should be optimized in catalyst iii, where the support cerium oxide was thoroughly reduced through the doped Ni.On reduced Ni/CeO2, the Ru cluster implantation can be done at low temperature (588 K).Obtained values of rRu-Ru at 2.62 Angstroem (N = 7.1) and rRu-O(s) (O(s) is the oxygen atom at surface) at 2.12 Angstroem (N = 1.2) by EXAFS for Ru3-Ni/CeO2 suggested a flat Ru cluster model comprised of several Ru atoms on reduced Ni/CeO2-x surface.The H(a)/Rutotal ratio exceeded unity for catalysts i and iii, suggesting new H adsorption sites.The temperature-programmed desorption for hydrogen (simultaneous desorption of HD and D2 for iii at 330-430 K suggested that the H at the new site and H on Ru surface were exchangeable above 330 K.The reservoir effect of the new site for H on catalysis is discussed in relation to new kinetic design of hydrogenation catalyst.
Hinsvark, O. N.,Stone, K. G.
, p. 334 - 337 (1956)
Influence of molybdenum on ceria activity and CO2 selectivity in propene total oxidation
Flouty,Abi-Aad,Siffert,Aboukais
, p. 219 - 226 (2004)
A total oxidation of propene into CO2 is obtained on pure ceria at 673 K. However, in the presence of molybdenum, propene can be partially oxidized at room temperature. The Electron Paramagnetic Resonance (EPR) indicates changes in the oxidation state of molybdenum occurring upon interaction with propene. It has been found that the concentration of Mo(V) influences the propene conversion. The interaction between propene and molybdenum leads to the formation of surface species that, depending on the strength of their bonding to the surface, can be decomposed to ethene or coke. These results have been confirmed by infrared (FTIR) study. The oxidation reaction of propene is in competition with that of coke or ethene deposit on the catalyst surface, which can explain the decrease of the catalyst activity and selectivity in the presence of high molybdenum loadings.
Size Dependence of Lattice Parameter and Electronic Structure in CeO Nanoparticles
Beck, Aaron,Bonani, Walter,Eloirdi, Rachel,Engelhard, Mark H.,Gouder, Thomas,Guo, Xiaofeng,Kriegsman, Kyle W.,Kvashnina, Kristina,Martin, Philippe,Popa, Karin,Prieur, Damien,Scheinost, Andreas C.,Vitova, Tonya,Walter, Olaf
, (2020)
Intrinsic properties of a compound (e.g., electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. Here, we explore the size dependence of both crystal and electronic properties of CeO nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. X-ray diffraction, X-ray photoelectron spectroscopy, and high-energy resolution fluorescence-detection hard X-ray absorption near-edge structure (HERFD-XANES) spectroscopy demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of CeIV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to Fourier transform infrared spectroscopy and thermogravimetric analysis measurements. In addition, the size dependence of the t2g states in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.
Copper nanoparticles supported on CeO2 as an efficient catalyst for click reactions of azides with alkynes
Amini, Mojtaba,Hassandoost, Ramin,Bagherzadeh, Mojtaba,Gautam, Sanjeev,Chae, Keun Hwa
, p. 13 - 16 (2016/07/20)
Readily prepared copper nanoparticles supported on CeO2 have been found to effectively catalyse the 1,3-dipolar cycloaddition (CuAAC) of a variety terminal alkynes and organic azides generated in situ from sodium azide and different organic halides furnishing the corresponding 1,2,3-triazoles in excellent yields. Cu nanoparticles supported on CeO2 have been characterized by X-ray diffraction analysis, energy dispersive X-ray analysis, scanning electron microscope and transmission electron microscope. The salient features of the present protocol are shorter reaction time, mild reaction conditions, reusability of the catalyst, and applicability to a wide range of substrates.
