12016-69-2Relevant articles and documents
Three-dimensionally ordered macroporous spinel-type MCr2O4 (M = Co, Ni, Zn, Mn) catalysts with highly enhanced catalytic performance for soot combustion
Wang, Jinguo,Yang, Gaoyang,Cheng, Li,Shin, Eun Woo,Men, Yong
, p. 4594 - 4601 (2015)
Three-dimensionally ordered macroporous (3DOM) spinel-type MCr2O4 (M = Co, Ni, Zn, Mn) catalysts were successfully prepared by a colloidal crystal template strategy and characterized by means of XRD, FE-SEM, BET, FT-IR, H2-TPR and O2-TPD. The 3DOM catalysts exhibited superior activity to their corresponding bulk counterparts, which were used as reference benchmarks in this study, due to the enlarged contact between the catalyst and the soot particle and improved mass transfer caused by the unique well-defined 3DOM structures. Meanwhile, the factors influencing the catalytic activity of the 3DOM catalysts in soot combustion were also optimized, such as metallic cations and feed compositions. Furthermore, the 3DOM catalysts displayed strong durability against structural collapse due to the robust 3DOM structure, demonstrating their promising potential in view of the practical working conditions of diesel engines.
Kanomata, T.,Tsuda, T.,Yasui, H.,Kaneko, T.
, p. 196 - 198 (1988)
Chemical compatibility of perovskite-type oxide La0.7Ca0.3Cr1-yCoyO3 with Y2O3 stabilized ZrO2
Kamata, Hiroyuki,Hosaka, Akio,Mizusaki, Junichiro,Tagawa, Hiroaki
, p. 679 - 688 (1995)
In order to evaluate the compatibility between the SOFC (Solid Oxide Fuel Cells) interconnector material of the perovskite-type La0.7Ca0.3Cr1-yCoyO3 (y = 0.05, 0.1 and 0.2) and 8 mol%Y2O3-ZrO2 (YSZ), two types of experiments were carried out in air. One was by the reaction of powder mixtures. The reaction products were identified by X-ray analysis after heating at 1000-1300 °C. The other was the experiments using diffusion couples. The distribution of elements at the interface was observed by EPMA for the couples heated at 1300 °C and 1400 °C. The reaction progressed mainly by the dissolution of calcium ions from the perovskite phase into YSZ. In the perovskite phase, due to the loss of A-site Ca ion, the activity of B-site ions increased, resulting in the deposition of the spinel-type CoCr2O4. The excess amount of calcium ions incorporated in YSZ reacted ZrO2 to form CaZrO3. Increase of cobalt content enlarge the reactivity of the perovskite phase with YSZ. The parabolic rate constant of the reaction, kp, was determined by the thickness of CaZrO3 at the interface of the diffusion couples. Calculated kp were 2.9×10-12cm2sec-1 and 2.1×10-11cm2sec-1 at 1300 °C and 1400 °C, respectively. For the practical application as the SOFC interconnector material, the content of cobalt as a sintering accelerator in (La, Ca)CrO3 must be controlled at low level to keep the chemical interaction to a minimum.
Highly Ordered Mesoporous Cobalt-Containing Oxides: Structure, Catalytic Properties, and Active Sites in Oxidation of Carbon Monoxide
Gu, Dong,Jia, Chun-Jiang,Weidenthaler, Claudia,Bongard, Hans-Josef,Spliethoff, Bernd,Schmidt, Wolfgang,Schüth, Ferdi
, p. 11407 - 11418 (2015)
Co3O4 with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co3+ is considered to be the active site, while tetrahedrally coordinated Co2+ is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H2 reduction of nanocast Co3O4 at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co2+ octahedrally coordinated by lattice oxygen in Fm3ˉm symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co2+ to Co3+ causes the high activity. Other mesoporous spinels (CuCo2O4, CoCr2O4, and CoFe2O4) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co3+ highly active but also the octahedrally coordinated Co2+ species in CoFe2O4 with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co2+ species is easily oxidized and shows high catalytic activity for CO oxidation.
Evolution of ferrimagnetism in Co(Cr1?xAlx)2O4(x=0.0?1.0)
Padam,Ravi,Pal
, p. 231 - 235 (2016)
Here we report on the preparation, structural and magnetic properties of solid solutions of Co(Cr1?xAlx)2O4. Substituted Al ions are found to occupy the B-site of the spinel structure. Enhancement in the magneti
Synthesis and anomalous magnetic properties of CoCr2O4 nanocrystallites with lattice distortion
Li, Shandong,Zhao, Guoxia,Bi, Hong,Huang, Zhigao,Lai, Heng,Gai, Rongquan,Du, Youwei
, p. 448 - 451 (2006)
Nanocrystalline Cobalt chromite (CoCr2O4) ceramic has been synthesized under a mild condition, rather than by a high-temperature sintering (e.g. >1673 K, in general). A shifted hysteresis loop with an exchange-bias field of 35.7 kA/m and a high coercivity of 627.9 kA/m at 4.2 K was achieved under the cooling field of 2.39×106 A/m. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results reveal that a strong lattice distortion and a large amount of surface defects exist in CoCr2O4 nanocrystallites (NCs). The anomalous magnetic properties, such as bias field and large coercivity, are attributed not only to the nanosize effect but also to the lattice distortion and crystal defects.
Thermolysis of [Co(NH3)6][Cr(C2O 4)3]
Pechenyuk,Domonov,Belyaevskii
, p. 1221 - 1226 (2008)
Thermolysis of the double-metal complex [Co(NH3) 6][Cr(C2O4)3] was studied in air at 200, 350, and 500°C and in a hydrogen atmosphere at 200, 350, 500, 700, and 900°C, as well as the composition and properties of thermolysis products. Oxidative thermolysis produces mixed oxides CoCr2O4 and Co2CrO4; reductive thermolysis produces Co + Cr 2O3 mixture. Specific surface areas were measured for reductive thermolysis products; the maximal specific surface area and, therefore, maximal dispersion are reached at 500°C. The morphology of the reductive thermolysis products and the thermolysis chemism were studied in relation to the nature of the complex anion.
Pressure derivatives of the Curie temperature of spinel-type CoCr2O4 and CoMn2O4
Tamura Syuzo
, (1993)
The magnetic permeability of CoCr2O4 and CoMn2O4 at high pressures has been measured in a piston-cylinder apparatus. The Curie temperature or the temperature of the Hopkinson peak of CoCr2O4 increases with pressure at a range of -0.1±0.1 to -0.3±0.2 K GPa-1 or -0.26±0.06 to -0.17±0.09 K GPa-1, respectively; namely, these are negative pressure derivatives and those of CoCr2O4 increase with pressure at a rate of 1.5±0.2 to 2.7±0.2 K GPa-1 or 1.37±0.08 to 1.9±0.4 K GPa-1, respectively.
Thermoprogrammed reduction and thermoprogrammed desorption studies of Co and Cr bimetallic oxides
Teodorescu,Georgescu,Sitaru,Vass,Segal
, p. 307 - 313 (1996)
Bulk (unsupported) bimetallic oxide catalysts and those supported on alumina and alumosilica (type 4Co-1Cr) have been investigated by thermoprogrammed reduction (TPR) and thermoprogrammed desorption (TPD) techniques. Influences of the support and the prep
Preparation of fine particle chromites. A combustion approach
Manoharan,Kumar,Patil
, p. 731 - 738 (1990)
Fine particle metal chromites, MCr2O4 where M = Mg, Mn, Fe, Co, Ni, Cu and Zn have been obtained by the combustion of a redox mixture containing corresponding divalent metal nitrate, chromium (III) nitrate and tetraformal trisazine (TFTA). An aqueous saturated solution of the redox mixture when rapidly heated at 350°C boils, foams and ignites to yield voluminous, fine particle chromite powder. Formation of chromite was confirmed by X-ray diffraction pattern and IR spectra. Fine particle nature of chromites was studied using particle size analysis, surface area measurements, TEM and SEM. The particle size of chromites is below lum and the surface area ranges from 13 to 30 m2/g.
Three-dimensionally ordered macroporous CoCr2O4-supported Au–Pd alloy nanoparticles: Highly active catalysts for methane combustion
Wang, Zhiwei,Deng, Jiguang,Liu, Yuxi,Yang, Huanggen,Xie, Shaohua,Wu, Zhixing,Dai, Hongxing
, p. 467 - 476 (2017)
Three-dimensionally ordered macroporous CoCr2O4 (3DOM CoCr2O4) and its supported Au–Pd alloy (xAuPdy/3DOM CoCr2O4; x = 0.98 and 1.93 wt%; Pd/Au molar ratio (y) = 1.93–1.96) nanocatalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of a number of techniques, and their catalytic activities were evaluated for methane combustion. The 3DOM CoCr2O4 and xAuPdy/3DOM CoCr2O4 samples possessed a high-quality 3DOM structure and a surface area of 33–36 m2/g. The Au–Pd alloy nanoparticles (NPs) with an average size of 3.3 nm were uniformly dispersed on the surface of the samples. The 1.93AuPd1.95/3DOM CoCr2O4 sample showed the best catalytic performance: the T10%, T50%, and T90% (temperatures required for achieving methane conversion of 10, 50, and 90%, respectively) were 305, 353, and 394 °C at a space velocity (SV) of 20,000 mL/(g h). The effects of SV, water vapor, and sulfur dioxide on the catalytic activity of the 1.93AuPd1.95/3DOM CoCr2O4 sample were also examined. It is concluded that the excellent catalytic performance of 1.93AuPd1.95/3DOM CoCr2O4 was associated with the higher surface area and adsorbed oxygen species concentration, better low-temperature reducibility, and strong interaction between Au–Pd alloy NPs and 3DOM CoCr2O4.
Casado, P. Garcia,Rasines, I.
, p. 787 - 790 (1986)
Structure and magnetic phase transitions in (Ni1? xCox)Cr2O4 spinel nanoparticles
Mohanty,Venter,Sheppard,Prinsloo
, (2020)
NiCr2O4 and CoCr2O4 are two distinct members of the chromite family (ACr2O4) having unique structural and magnetic properties. This paper is a continuation of previous work [Mohanty et al., J. Magn. Magn. Mater. 451(2018)20] and is focused on the modification of ferrimagnetic properties in NiCr2O4 by substituting Co ions at Ni sites. In order to do so (Ni1? xCox)Cr2O4 (x = 0, 0.50, 0.75, 1.00) powder samples were synthesized using chemical co-precipitation techniques. Interest is primarily on (Ni0.5Co0.5)Cr2O4 and (Ni0.25Co0.75)Cr2O4 as characterization results on the end members have been reported. It was determined with in-situ temperature dependent X-ray diffraction measurements that these compositions become fully crystallized cubic spinels with space group Fd3-m above 700 °C. All samples were subsequently calcined at 900 °C to ensure phase purity and uniform crystallinity. Transmission electron microscopy showed non-uniform distribution of particle sizes with the majority of the particles having bi-pyramidal structures with flat tops for both samples. A comparative account of different ferrimagnetic Curie temperature, θf or TC, estimations are presented as determined from measured temperature dependences of the following techniques: Fits of the magnetic susceptibility data indicated a minimum value for the (Ni0.5Co0.5)Cr2O4 sample at 56.1 ± 0.9 K, followed by an increase to 76.8 ± 0.4 K for the (Ni0.25Co0.75)Cr2O4 sample; Neutron diffraction measurements gave values of 80 ± 1 K and 87 ± 1 K; Their paramagnetic Curie points, θp, were determined to be 73.3 and 84.9 K, respectively. The magnetic frustration index f = ΘCW/TC was found to decrease continuously over the series from 11.9 for NiCr2O4 to 7.1 and 6.5 for x = 0.5 and 0.75 respectively with (Ni0.5Co0.5)Cr2O4 being more frustrated than (Ni0.25Co0.75)Cr2O4. Magnetization as a function of applied magnetic field measured at 3 K demonstrates unusually high coercivity for (Ni0.5Co0.5)Cr2O4, supporting the notion for the higher degree of magnetic frustration in this sample. No exchange bias was observed for M (μ0H) in the (Ni0.25Co0.75)Cr2O4 sample measured at 3 K, but did however show a significant anomaly in its hysteresis loop at this temperature. The anomaly in hysteresis behaviour disappeared when measured at 1.7 K and also at higher temperatures. Frequency dependent ac-susceptibility measurements revealed no shift in the peak position with frequency refuting the existence of spin-glass like behavior in both these samples.
