共查询到20条相似文献,搜索用时 31 毫秒
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目前中国广泛采用以三氧化二铝为载体、以金属盐作活性组分制备合成甲基异丙基酮的催化剂.合成甲基异丙基酮的关键是催化剂的制备技术.为了改善催化剂的选择性,提高合成产物的收率,以异丁酸和乙酸为原料、以In/TiO2为催化剂合成甲基异丙基酮.研究了催化剂活性组分、催化合成反应温度、原料异丁酸和乙酸的配比、催化剂的再生等因素对催化合成反应的影响.确定了合成甲基异丙基酮的最佳条件:稀土活性组分的质量分数15.0%,合成温度430~450℃,异丁酸与乙酸的物质的量比1.0:1.5,反应空速0.6~0.7h-1.在此条件下转化率>90%,催化剂选择性>80%. 相似文献
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综述了Ln(B1/2Ti1/2)O3 (B=Mg, Zn, Co)型微波介质陶瓷的结构、低温烧结及改性研究现状. 少量烧结助剂可有效降低陶瓷的烧结温度,但有时会恶化品质因数(Q×f). 离子取代可显著提高Q×f值,对谐振频率温度系数(τf)无明显影响;而复合改性则可有效调节τf值至近0. 最后探讨了Ln(B1/2Ti1/2)O3型微波介质陶瓷研究中存在的问题和未来的发展趋势,简化和优化合成工艺、实现低温烧结和调节谐振频率温度系数、加强低温烧结、离子取代和复合改性的机理研究是未来重要的研究方向. 相似文献
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本文采用空气中一次高温还原烧成、快冷至中温氧化新工艺,系统地研究了稀土氧化物Ln_2O_3(Ln—La、Sm、Dy)掺杂对SrTiO_3半导瓷晶界阻挡层电容器(简称GBBLC)结构和性能的影响。获得了介电常数ε≥50000、介质损耗tgδ≤0.010、绝缘电阻率ρ≥10~(10)Ω·cm、介电常数温度系数(-25℃—85℃)α=±(10—12)%的La_2O_3掺杂SrTiO_3GBBLC_o其综合性能、稳定性、重复性好。实验结果表明:不同种类的La_2为_3掺杂对SrTiO_3显微结构和性能有很大彤响。提出了不同掺杂量时,Ln_2O_3掺杂SrTiO_2的晶粒缺陷机制。用XRD测定了Ln_2O_3掺杂SrTiO3的晶胞常数,SEM分析显示:Dy_2O_3、Sm_2O_3掺杂比La_2O_3掺杂的SrTiO_3晶粒生长缓慢,且Sm_2O_3掺杂的SrTiO_3晶粒生长呈取向分布。研究了非化学计量比对稀土氧化物掺杂SrTiO_2GBBLC的影响:探讨了烧成制度对性能的影响。 相似文献
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合成了稀土高氯酸盐与咪唑、DL α 丙氨酸的4种配合物晶体。经傅里叶变换红外光谱(FTIR)、元素分析和化学分析测定后确定其组成为[Ln(C3H7NO2)x(C3H4N2)(H2O)](ClO4)3(Ln=La,x=3;Ln=Pr,Nd,Sm,x=2)。用差示扫描量热法(DSC)测定了4种配合物的热分解数据,4个配合物开始熔化分解的温度分别为502 5K,532 4K,495 7K,516 7K,配合物有较高的热稳定性。 相似文献
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New hetero-dilanthanide β-diketonate complexes of the type [Ln1Ln2(fod)6(μ-bpm)] {fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione; bpm = 2,2′-bipyrimidine; Ln1 = Pr and Ln2 = Nd (1); Ln1 = Nd and Ln2 = Sm (2); Ln1 = Eu and Ln2 = Tb (3) and Ln1 = Ho and Ln2 = Er (4)} have been isolated by reacting sequentially, the coordinatively unsaturated Ln(fod)3 chelates of two different lanthanides and 2,2′-bipyrimidine bridging ligand in 1:1:1 molar ratio, in ethanol. The purity and hetero-dilanthanide nature of the complexes has been confirmed by NMR, 4f–4f absorption spectroscopies and electrospray mass spectrometry. The oscillator strength of the hypersensitive transitions confirms the presence of the two different lanthanides in the complexes in 1:1 ratio. The complexes 2 and 3 display strong pink and red luminescences, respectively. The intramolecular Tb(III) → Eu(III) energy transfer has been observed in complex 3. 相似文献
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《Journal of the European Ceramic Society》2019,39(14):4275-4282
Yb/Ln (Ln=Er, Tm) doped TeO2-based glasses containing CsPbBr3 perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr3 exciton recombination under UV excitation, and produce Er3+ green, Er3+ red and Tm3+ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln3+ emissions will be quenched with the precipitation of CsPbBr3 in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr3 rather than energy transfers from Ln3+ to CsPbBr3. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr3 and upconversion luminescence of Er3+ related to pristine ones are retained after immersing the products in water up to 30 days. 相似文献
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介绍了 Ln2 O3 / x- 13分子筛担载型催化剂的制备方法 ,并通过实验说明了 Ln2 O3 / x- 13分子筛在合成DOP(邻苯二甲酸二辛酯 )中的高催化活性 相似文献
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X-ray crystallography reveals four isostructural lanthanide polymeric solids, [Ln2(atp)3(H2O)2]·dmf·4H2O (atp = 2-aminoterephthalate; dmf = N,N′-dimethylformamide; Ln = La (1), Ce (2), Pr (3) and Nd (4), respectively) that are obtained from the solvothermal synthesis which are crystallized in an interesting 3D polymeric framework with a (4,4,6)-linked {42·84}{44·62}2{48·66·8}2 fsy net topology. Upon excitation at 350 nm, they all show the solid state ligand-centered luminescences but both 2 and 3 also exhibit the weak lanthanide-based characteristic emissions in the visible region at room temperature. The cyclic voltammetric investigation indicates that 2 exhibits appreciable electrochemical activity for formaldehyde. 相似文献
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研究了稀土顺丁橡胶(Ln-BR)与天然橡胶(NR)以不同比例共混后生胶、混炼胶和硫化胶的性能,并与相同条件下的镍系顺丁橡胶(Ni-BR)/NR共混胶的性能进行了对比,结果表明,共混胶随Ln-BR用量的增大,ML^100℃1+4降低,工艺行为良好,硫化胶力学性能、磨耗、湿滑指数和生热值下降,并且Ln-BR/NR硫化胶的抗湿滑性和动态疲劳性均优于Ni-BR/NR硫化胶。 相似文献
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采用微波水热合成法,在不添加任何表面活性剂或者模版的条件下,快速合成了系列NaGd(WO4)2:Ln3+(Ln=Tb, Dy, Sm, Eu)荧光粉。探讨了pH值、反应温度和反应时间对样品物相结构、微观形貌及发光性能的影响。结果表明:反应体系pH值为8.0,在180 ℃下反应60 min即可合成四方晶系NaGd(WO4)2的纯相,且结晶良好,形貌为规整的四方盘。所合成的NaGd(WO4)2:Ln3+ 系列荧光粉的激发光谱均由两部分组成:200~300 nm的宽激发带归属于W-O、Ln-O之间的电荷转移;300~500 nm的系列尖峰归属于Ln3+的特征f-f跃迁。系列样品均可被近紫外光有效激发,当Ln3+为Tb3+、Dy3+、Sm3+和Eu3+时,分别呈现绿、黄、橙红和红光发射。 相似文献
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Gheorghiţa Mitran Adriana Urda Nathalie Tanchoux François Fajula Ioan-Cezar Marcu 《Catalysis Letters》2009,131(1-2):250-257
Ln–Mg–Al mixed oxide catalysts (Ln = Ce, Sm, Dy, Yb) were prepared from layered double hydroxide precursors, characterized using XRD, N2 adsorption, TG-DTG, EDX, H2-TPR and CO2-TPD techniques and tested in the oxidative dehydrogenation of propane in the temperature range 450–600 °C. For all the catalysts the conversion increases with increasing the reaction temperature while the propene selectivity decreases to the benefit of carbon oxides for Ce-based system and of cracking products for the others. The best yields in propene were obtained with Dy- and Sm–Mg–Al–O catalysts. No correlation between the reducibility of the rare-earth cation and the catalytic performances was observed. A linear correlation between the catalyst basicity and the propene selectivity was evidenced. 相似文献
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以锌(Ⅱ)离子为模板分步合成法获得了大环配体单核锌配合物,在此基础上引入稀土离子获得Ln(Ⅲ)—Zn(Ⅱ)(Ln=Eu,Tb)杂核配合物。用IR、UV、ES—MS等手段对配合物进行了表征。Eu(Ⅲ)—Zn(Ⅱ)大环配合物在己腈溶液中检测到Eu(Ⅲ)离子特征荧光发射。 相似文献
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