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471.
472.
Mg-Fe尖晶石复合氧化物对苯乙烯选择氧化反应的催化性能 总被引:8,自引:0,他引:8
研究了以H2O2为氧化剂时Mg-Fe尖晶石复合氧化物催化剂对苯乙烯选择氧化制苯甲醛反应的催化性能.结果表明,非化学计量比的Mg-Fe尖晶石复合氧化物催化剂的活性优于纯MgFe2O4尖晶石相,苯甲醛产率达到20%左右.在非化学计量比的Mg-Fe尖晶石复合氧化物中掺入适量的Al3+后,可进一步提高催化活性,苯甲醛最高产率达到33.4%.催化剂表征数据揭示,非化学计量比的Mg-Fe和Mg-Fe-Al复合氧化物催化剂是由纳米尺度的铁酸盐尖晶石和α-Fe2O3微晶相构成的.除了非化学计量比尖晶石具有较多的缺陷结构外,α-Fe2O3微晶相的存在也可能是造成非化学计量比催化剂活性高的原因之一. 相似文献
473.
Tomokazu Ito Akihiko Nakatsuka Hideki Maekawa Akira Yoshiasa Takamitsu Yamanaka 《无机化学与普通化学杂志》2000,626(1):42-49
The crystal structures of MgAl2–xGaxO4 (0 ≤ x ≤ 2) spinel solid solutions (x = 0.00, 0.38, 0.76, 0.96, 1.52, 2.00) were refined using 27Al MAS NMR measurements and single crystal X‐ray diffraction technique. Site preferences of cations were investigated. The inversion parameter (i) of MgAl2O4 (i = 0.206) is slightly larger than given in previous studies. It is considered that the difference of inversion parameter is caused by not only the difference of heat treatment time but also some influence of melting with a flux. The distribution of Ga3+ is little affected by a change of the temperature from 1473 K to 973 K. The degree of order‐disorder of Mg2+ or Al3+ between the fourfold‐ and sixfold‐coordinated sites is almost constant against Ga3+ content (x) in the solid solution. A compositional variable of the Ga/(Mg + Ga) ratio in the sixfold‐coordinated site has a constant value through the whole compositional range: the ratio is not influenced by the occupancy of Al3+. The occupancy of Al3+ is independent of the occupancy of Ga3+, though it depends on the occupancy of Mg2+ according to thermal history. The local bond lengths were estimated from the refined data of solid solutions. The local bond length between specific cation and oxygen corresponds with that expected from the effective ionic radii except local Al–O bond length in the fourfold‐coordinated site and local Mg–O bond length in the sixfold‐coordinated site. The local Al–O bond length in the fourfold‐coordinated site (1.92 Å) is about 0.15 Å longer than the expected bond length. This difference is induced by a difference in site symmetry of the fourfold‐coordinated site. The nature that Al3+ in spinel structure occupies mainly the sixfold‐coordinated site arises from the character of Al3+ itself. The local Mg–O bond length in the sixfold‐coordinated site (2.03 Å) is about 0.07 Å shorter than the expected one. Difference Fourier synthesis for MgGa2O4 shows a residual electron density peak of about 0.17 e/Å3 in height on the center of (Ga0.59 Mg0.41)–O bond. This peak indicates the covalent bonding nature of Ga–O bond on the sixfold‐coordinated site in the spinel structure. 相似文献
474.
为改善CuCr2O4黑色颜料呈色性能,将Fe3+掺杂进入CuCr2O4晶体中,采用共沉淀法制备CuCr2-xFexO4(x=0,0.04,0.05,0.06,0.07),并对所制备样品进行TG-DTA、XRD、SEM、Raman、XPS、UV-Vis吸收光谱和色度值的测试与表征。结果表明,Fe以三价态固溶进入Cr3+位置,未出现杂质相,得到的CuCr2-xFexO4晶粒细小、分散均匀。Fe3+掺杂可减小CuCr2O4的禁带宽度,从1.25 eV减小到1.08 eV,禁带宽度的减小是由于2p(O2-)→3d(Fe3+)和Fe3+的d-d(6A1g→4T1g和 6A1g→4T2g)电荷跃迁引起的。禁带宽度的减小使得黑色颜料对可见光(380~780 nm)的吸收率提高,L*值减小,呈现出良好的黑度。得到的最佳黑色颜料为CuCr1.95Fe0.05O4,L*=17.63,a*=-0.77,b*=-1.61。 相似文献
475.
Dr. Youssef Doubi Prof. Bouchaib Hartiti Prof. Maryam Siadat Prof. Hicham Labrim Prof. Salah Fadili Prof. Mounia Tahri Prof. Mohamed Stitou Prof. Philippe Thevenin Etienne Losson 《欧洲无机化学杂志》2023,26(22):e202300047
The semiconductor realization is a very significant stage in gas sensor application. Herein, the Mn3O4 semiconductor was deposited using chemical spray pyrolysis. The effect of deposition temperature on structural, vibrational optical and electrical Mn3O4 thin layers properties were investigated through: X-ray diffraction, Raman spectroscopy, UV-visible spectrophotometer, and two points electrometers respectively. The X-ray diffraction showed the appearance of spinel phase of tetragonal Mn3O4 with strong formation direction along (101) plan and without any secondary phase indicating the formation of pure Mn3O4. The Raman spectroscopy confirmed the results obtained in XRD and certified the high-quality formation of Mn3O4. In addition, the crystallinity improvement (the increase of crystallite size and the decrease of dislocation density) was caused by the increasing of deposition temperature from 350 °C to 450 °C. Optical properties such as transmittance, absorbance and band gap energy were extracted by UV-Visible spectrophotometer. Thus, low transmittance, high absorbance and small band gap energy were observed at the highest substrate temperature (450 °C). The electrical conductivity showed good values between 4.83 and 13.89 mS.cm−1. These properties make Mn3O4 an appropriate material to be used as a sensitive layer in gas sensors applications. 相似文献