The correlations between structural and optical properties of magnetite nanoparticles synthesised from natural iron sand

The correlations between structural and optical properties of magnetite (Fe₃O₄) nanoparticles were analyzed by using X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. The magnetite was synthesised from the iron sand using NaOH, HCl, and NaCl as a solvent. From the quantitative analysis of XRD spectra, the crystallite size (D), strain ($\epsilon$), stress ($\sigma$), energy deformation (u), porosity, and specific surface area were determined. The Kramers Kronig (K–K) relations was applied to the FTIR spectra to determine the optical properties: refractive index (n), extinction coefficient (k), the complex dielectric function ($\mathit{\epsilon }$), and the energy loss function (Im(-1/ε)). The uniform strain was produced from the NaOH and HCl as the solvent. The magnetite had higher porosity with NaCl as a solvent and was directly proportional to the optical phonon vibration. We found a perfect correlation; when the difference between two optical phonon increases, the crystallite size decreases, and the strain will be uniform.     

Anionic Clays as Potential Slow-Release Fertilizers: Nitrate Ion Exchange

Several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO₃ ^– release were determined to test their suitability as slow-release N fertilizers. A sample (Mg:Al = 2:1) synthesized at 60°C with smaller particle size released 75, 86 and 100% of its NO₃ ^– in 1, 3 and 7 days, respectively when equilibrated with a simulated soil solution. On the other hand, the 175°C/2 hrs sample with larger particle size released 65, 77 and 84% of its nitrate in 1, 3 and 7 days, respectively. Another anionic clay (synthesized at 175°C/24 hrs) of higher charge density (Mg:Al = 2:1) containing NO₃ ^– was equilibrated with a 0.012 N NaCl or Na₂CO₃ to test the role of different anions in releasing the NO₃ ^– anion from the interlayers. The results showed that Cl^– released more NO₃ ^– than did CO₃ ^2– from this anionic clay after all the treatment times probably as a result of the CO₃ ^2– anion blocking the release of NO₃ ^– from the interior of the crystals. When a lower charge density (Mg:Al = 3:1) sample (synthesized at 175°C/48 hrs) was equilibrated with 0.02N solution of anions the release of nitrate was as follows: Cl^– < F^– < SO₄ ⁼ CO₃ ^2–. These results suggest that the divalent SO₄ ⁼ and CO₃ ^2– anions are more effective in the release of NO₃ ^– from this lower charge density anionic clay. Time-resolved structural analysis of NO₃ ^– exchange with CO₃ ^2– in the above anionic clay using synchrotron x-ray diffraction showed that ion exchange is rapid because of small crystal size and lower charge density. Thus the release of NO₃ ^– from anionic clays is an interplay among the type of anions present in soil solution, their concentration, pH of soil solution, the charge density and crystal size of anionic clay etc.     

Sol-Gel法制备氧化铝负载铜基超细粒子影响因素的研究

通过对Sol-Gel法制备氧化铝负载铜基超细粒子的研究，表明PEG分散剂对粒度分布有重要影响；采用XRD对制得的催化剂表面组成进行了研究，指出了发生固相反应生成活性较低的CuAl2O4的影响因素。     

Reforming of methane with carbon dioxide over supported bimetallic catalysts containing Ni and noble metal: I. Characterization and activity of SiO2 supported Ni–Rh catalysts

Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m²/g), large pore volume (∼5 cm³/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C₁₀₊ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C₉–C₁₅ hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.     

Oxidative coupling of methane over LaCoO3−δ-based mixed oxides

The catalytic activity of LaCoO_3–-based mixed oxides for the oxidative coupling of methane has been tested by TPR and cyclic reaction. Characterization has been done by XRD, TGA and Mössbauer spectrometry. It is likely that the perovskite-crystal structure containing hypervalent metal ions has an important role and that unique structural oxygen species in the perovskite contribute to the partial oxidation of methane.     

反应过程中升华型催化剂的物性变化(Ⅱ) X—射线衍射结果

对衰化程度不同的升华型催化剂进行了 X—射线衍射测定。发现在使用过程中催化剂比表面迅速减小,但氯化汞-活性炭催化剂的新旧样品中,氯化汞均保持单层分散。但即将废弃的醋酸锌-活性炭催化剂上,醋酸锌的单层分散情况受到破坏,出现了醋酸锌晶相峰。晶相峰的出现可能与后期使用温度偏高引起烧结有关。晶相峰的出现会降低催化活性,使之不得不被废弃。     

Selectivities in methanol oxidation over silica supported molybdena

Selectivities in methanol oxidation over silica supported molybdenum oxide catalysts were investigated in relation with the phase distribution. The supported catalysts were prepared by impregnation with ammonium heptamolybdate. In addition to crystalline MoO₃, Mo containing cluster species of 1–2 nm size were observed by STEM even from a used catalyst with 13% catalyst loading. The percentage of Mo present as crystalline MoO₃ increases with the catalyst loading. An ESCA study indicates that part of surface Mo in the supported catalysts is reduced to Mo⁵⁺. The dimethyl ether selectivity increases with the catalyst loading and its formation occurs over the crystalline MoO₃ phase. The Selectivities to CO and methyl formate are greatly enhanced because of the presence of support, and are relatively independent of the catalyst loading and phase distribution. The dependence and independence of the Selectivities of different byproducts on the loading make the silica supported catalysts with high catalyst loadings less selective for the partial oxidation of methanol to formaldehyde.     

磨加工及残余应力对氮化硅陶瓷强度的影响

利用X-射线衍射方法测量了经不同磨削的氮化硅陶瓷表面残余应力及其对抗弯强度的影响。结果表明，磨削工艺所引入的残余应力是拉应力，对陶瓷抗弯强度有显著降低。     

Gold supported on ceria and ceria–alumina promoted by molybdena for complete benzene oxidation

New gold–molybdena catalysts supported on ceria and ceria–alumina in reaction of complete benzene oxidation were studied. The catalysts were characterized by means of XRD, TPR, XPS and Raman spectroscopy. High and stable catalytic activity was established in the temperature region 200–240 °C. The presence of gold causes a modification in ceria structure leading to an increase of Ce³⁺ and oxygen vacancies formation. The loading of Al³⁺ increases additionally the oxygen vacancies, while a tendency of decrease of Ce³⁺ amount was observed. The presence of alumina results also in a larger share of active oxygen species proved by analysis of O 1s XPS spectra. The differences in the activities within the starting temperature range (150–180 °C) and in the region of 100% conversion (200–240 °C) could be explained by supposing that in the LT region the electron transfer between nanosized gold and ceria particles via oxygen vacancies has a crucial role. In the HT region the oxygen mobility, provoked by the defective structure of ceria due to the presence of Al³⁺, becomes of prevailing importance. It was also concluded that alumina prevents the gold and ceria agglomeration, which is the main factor to avoid deactivation under extreme reaction conditions.