Adsorption of the lanthanum and thorium cryptates at mercury electrode

The adsorption behavior of cryptates of La³⁺ and Th⁴⁺ cations at the Hg/aqueous solution interface is studied by using the electrochemical impedance spectroscopy method. It was shown that the studied complexes have high surface activity at the interface. The lanthanum cryptate adsorption parameters are found using the regression analysis based on the two parallel capacitor model supplemented by the Frumkin adsorption isotherm. The differential capacitance curves calculated by using these parameters agree satisfactorily with the experimental ones. The more complicated adsorption behavior of lanthanum cryptate, as compared with the complexes of lower valence cations, is interpreted with taking into consideration the strong interaction of the La³⁺ cation contained in the [2.2.2.] cryptand intramolecular cavity with the supporting electrolyte anions.     

Carbon dioxide reforming of methane on monolithic Ni/Al2O3-based catalysts

Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal (Na, K) oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess.     

Dehydrogenation of Amine?Borane Me2NH⋅BH3 Catalyzed by a Lanthanum?Hydride Complex

The rare‐earth‐metal? hydride complexes [{(1,7‐Me₂TACD)LnH}₄] (Ln=La 1 a , Y 1 b ; (1,7‐Me₂TACD)H₂=1,7‐dimethyl‐1,4,7,10‐tetraazacyclododecane, 1,7‐Me₂[12]aneN₄) were synthesized by hydrogenolysis of [{(1,7‐Me₂TACD)Ln(η³‐C₃H₅)}₂] with 1 bar H₂. The tetrameric structures were confirmed by ¹H NMR spectroscopy and single‐crystal X‐ray diffraction of compound 1 a . Both complexes catalyze the dehydrogenation of secondary amine? borane Me₂NH ? BH₃ to afford the cyclic dimer (Me₂NBH₂)₂ and (Me₂N)₂BH under mild conditions. Whilst the complete conversion of Me₂NH ? BH₃ was observed within 2 h with lanthanum? hydride 1 a , the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me₂NH ? BH₃ in various stoichiometric ratios gave a series of intermediate products, [{(1,7‐Me₂TACD)LaH}₄](Me₂NBH₂)₂ ( 2 a ), [(1,7‐Me₂TACDH)La(Me₂NBH₃)₂] ( 3 a ), [(1,7‐Me₂TACD)(Me₂NBH₂)La(Me₂NBH₃)] ( 4 a ), and [(1,7‐Me₂TACD)(Me₂NBH₂)₂La(Me₂NBH₃)] ( 5 a ). Complexes 2 a , 3 a , and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me₂NH ? BH₃” fragments that were trapped within the coordination sphere of a rare‐earth‐metal center.     

Diels–Alder and Retro‐Diels–Alder Cycloadditions of (1,2,3,4,5‐Pentamethyl)cyclopentadiene to La@C2v‐C82: Regioselectivity and Product Stability

One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5‐pentamethylcyclopentadiene (Cp*) with La@C_2v‐C₈₂ were investigated. The attack of Cp was proposed to occur on bond 19 , whereas that of Cp* was confirmed by X‐ray analysis to be over bond o . Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C_2v‐C₈₂Cp was one order of magnitude faster than that of La@C_2v‐C₈₂Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C_2v‐C₈₂ to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C₈₂Cp and La@C₈₂Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o . This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C₈₂ singly occupied molecular orbital. In addition, we show that the higher stability of the La@C₈₂Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long‐range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C₈₂Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult.     

染料敏化太阳能电池对电极La2Mo2O7复合MWCNTs非Pt催化剂的制备与性能

通过高温固相法对醋酸镧（C₆H₉O₆La·xH₂O）与高钼酸铵（（NH₄）₆Mo₇O₂₄·4H₂O）在一定条件下热解制备非Pt催化剂La₂Mo₂O₇（La₂O₃-2MoO₂）。进一步采用2种方法将La₂Mo₂O₇与多壁碳纳米管（MWCNTs）进行复合,一种是将La₂Mo₂O₇喷涂到MWCNTs表层之上得到La₂Mo₂O₇/MWCNTs,另一种是将两者均匀混合掺杂得到La₂Mo₂O₇@MWCNTs,再将上述2种复合材料应用于染料敏化太阳能电池对电极进行相应研究。通过扫描电子显微镜（SEM）表征了复合催化材料的微观形貌,X射线衍射（XRD）确定了微观结构。采用电流密度-光电压曲线、循环伏安,交流阻抗以及塔菲尔极化分析了材料的光电性能。实验结果表明在电解液I₃^-/I^-中,基于La₂Mo₂O₇/MWCNTs与La₂Mo₂O₇@MWCNTs的对电极,相同的条件下在光电池中获得的光电转换效率分别为6.09%和4.84%,明显高于MWCNTs的3.94%和La₂Mo₂O₇的0.87%。电极性能的提高可归因于La₂Mo₂O₇复合催化剂相对大的比表面积和高导电性。     

稀土镧在腈纶纤维化学镀银中的应用及其电化学性能

采用化学镀法(镀液中加入适量的稀土镧)在硅烷偶联剂改性后的腈纶纤维表面沉积金属银,由粒径分析、X射线衍射、扫描电子显微镜、阴极极化曲线以及循环伏安曲线等方法对其进行表征,研究了硝酸镧对化学镀银沉积速度、镀层质量和电化学性能的影响。结果表明,镀银液中加入适宜的硝酸镧,银的沉积速率和腈纶纤维表面银镀层的表面质量均有不同程度的提高。电化学测试表明,镀银液中增大硝酸镧的浓度(0～0.01 g/L),阴极极化曲线极化度增大,氧化还原峰的电流上升,电沉积的速度加快。     

Ce3+掺杂La2O3的17O固体核磁共振研究

本文用水热共沉淀法制备Ce³⁺掺杂La₂O₃的前驱体,随后在H₂/N₂气氛下用高温煅烧法合成了不同Ce³⁺浓度的掺杂La₂O₃。由于Ce³⁺的掺杂,¹⁷O固体核磁共振谱图中在698、650和558处出现了新的共振峰;随着Ce³⁺掺杂浓度的增加,这些峰的强度也随之增强。根据谱峰位置和强度,对谱图进行了归属：698、650处的共振峰应源自与Ce³⁺相连的四配位O(OCeLa₃),558处的信号则来自于与Ce³⁺相连的六配位O(OCeLa₅)。通过¹⁷O固体核磁共振能够直接观测与Ce³⁺直接相连的O显示该方法将可能用于研究稀土掺杂氧化物功能材料。     

Performance of La2O3/InAlN/GaN metal—oxide—semiconductor high electron mobility transistors

We report on the performance of La2O3/InAlN/GaN metal-oxide-semiconductor high electron mobility transistors(MOSHEMTs) and InAlN/GaN high electron mobility transistors(HEMTs).The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device,while the gate leakage current in the reverse direction could be reduced by four orders of magnitude.Compared with the HEMT device of a similar geometry,MOSHEMT presents a large gate voltage swing and negligible current collapse.     

镧在细胞膜上键合形态研究

研究了一种简单快速的富膜细胞组分的提取和分离方法，并运用这种方法研究了大豆幼苗根细胞膜上La结合形态，La末与膜蛋白结合，而是与一非膜蛋白组分呈优势结合。