钙类质同像置换对钙钛矿型La1-xCaxCoO3热催化氧化甲苯性能的制约机制

挥发性有机物(VOCs)是大气光化学臭氧(O3)和细颗粒物(PM2.5)的重要前驱体,其有效减排是治理大气污染的重要环节。钙钛矿型复合氧化物具有催化氧化活性好、化学组成可控、热稳定性高等优点,在热催化氧化VOCs中具有较好的前景。本研究采用溶胶-凝胶法合成不同钙置换量的钙钛矿型钴酸镧(La1-xCaxCoO3),并以甲苯作为目标VOC,考查钙置换对钴酸镧(LaCoO3)热催化氧化甲苯性能的制约机制,结果表明,钙置换没有明显改变钴酸镧的晶体结构,但显著增强其热催化氧化活性。钙置换使钴酸镧颗粒尺寸减小,比表面积和堆积孔容增加,有利于减少气体扩散阻力。以甲苯降解率为50%所对应的温度(T50),以及反应温度为200℃时的比表面积标化CO2生成速率作为评价指标,系列样品的催化活性强弱为:LaCoO3(260℃,0.094μmolm-2s-1)<La0.9Ca0.1CoO3(232℃,0.114μmol m-2 s-1)<La0.7Ca0.3CoO3(225℃,0.118μmol m-2 s-1)<La0.8Ca0.2CoO3(212℃,0.135μmolm-2s-1)。随钙置换量增加,钴酸镧的单位比表面积催化活性呈现先增强后轻微减弱的趋势。系列样品的阳离子空位吸附氧密度未发生明显改变,但晶格氧释放速率显著提高,有利于催化氧化甲苯为CO2和H2O。随着钙置换量增加,晶格氧活性呈先增加后减少的趋势,从而导致催化活性也表现出类似的变化。

溶胶—凝胶法制备钙钛矿型复合氧化物La_(1-x)Ca_xCoO_3纳米晶

采用溶胶—凝胶法合成了 La1-x Cax Co O3 (X=0 .1 ,0 .3 ,0 .5 ,0 .7)纳米晶 ,采用 TGA技术确定干凝胶焙烧温度 ;XRD技术证明所合成粉体为钙钛矿型复合氧化物 La1-x Cax Co O3 ,其粒径为 2 0 nm左右 .实验表明 ,脱水温度 70— 80℃左右 ,p H值小于 5时较合适 .同时也考察了柠檬酸用量对溶胶、凝胶形成的影响 .

Ca_3La_3(BO_3)_5中Ce^(3+)、Pb^(2+)、Mn^(2+)的光致发光和能量传递

本文研究了Ca_3La_3(BO_3)_5体系中Ce^(3+)、Pb^(2+)、Mn^(2+)光致发光与组成的关系及Ce^(3+)、Pb^(2+)对Mn^(2+)发光的敏化作用。实验表明在254nm激发下,Ce^(3+)、Pb^(2+)均在紫外光区发光,而单激活的Mn^(2+)几乎不发光。Ce^(3+)、Pb^(2+)能敏化Mn^(2+)发光,且Ce^(3+)的敏化作用比Pb^(2+)强。Ce^(3+)-Mn^(2+)共激活的Ca_3La_3(BO_3)_5在紫外光激发下发出明亮的红光。Ce^(3+)-Mn^(2+)能量传递的机理为电多极相互作用的共振传递。

La_(2/3)(Ca,Ba)_(1/3)MnO_3系统的顺磁共振研究

报道了对La2/3Ca1/3MnO3和La2/3Ba1/3MnO3系统不同温度下的电子顺磁共振(EPR)实验研究,当温度高于某一特征温度Tmin时,共振线宽随温度降低而线性变窄;当温度低于Tmin时,共振线宽表现出反常展宽.基于“瓶颈(bottleneck)”自旋-晶格弛豫模型我们对这种行为进行了讨论,并且指出A位离子平均半径强烈影响着自旋-晶格交换作用和自旋-自旋相互作用的强弱.

Three-dimensional ordered macroporous perovskite-type La_(1-x)K_xNiO_3 catalysts with enhanced catalytic activity for soot combustion: the Effect of K-substitution

Three-dimensional ordered macroporous (3DOM) La1?xKxNiO3 perovskite-type catalysts were successfully prepared by a colloidal crystal template method and characterized by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray scattering elemental mapping, X-ray diffraction, Raman and X-ray photoelectron spectroscopy, and temperature-programmed reduction of H2. Further, their catalytic activity in soot combustion was determined by temperature-programmed oxidation reaction. K substitution into the LaNiO3 lattice led to remarkably improved catalytic activity of this catalyst in soot combustion. Amongst various catalysts, La0.95K0.05NiO3 exhibited the highest activity in soot combustion (with its T50 and CO2 S values being 338 °C and 98.2%, respectively), which is comparable to the catalytic activities of Pt-based catalysts under the condition of poor contact between the soot and the catalyst. K-substitution improves the valence state of Ni and increases the number of oxygen vacancies, thereby leading to increased density of surface-active oxygen species. The active oxygen species play a vital role in catalyzing the elimination of soot. The perovskite-type La1?xKxNiO3 nanocatalysts with 3DOM structure without noble metals have potential for practical applications in the catalytic combustion of diesel soot particles.

Fe掺杂LSCCF对中低温固体氧化物燃料电池ITSOFC短期输出性能的影响

柠檬酸盐法制备La0.7Sr0.15Ca0.15Co1-xFexO3-δ(x=0.2、0.4、0.6、0.8)阴极材料。该前驱体在900℃处理2h后,XRD证实已经形成完整的钙钛矿结构衍射峰。随Fe掺杂量增加,XRD谱图衍射峰的位置向小角度发生偏移,粉体的晶粒尺寸逐渐变大。SEM观察La0.7Sr0.15Ca0.15Co1-xFexO3-δ粉体其表面活性较高并出现了一定的团聚现象,颗粒尺寸约为5μm。以La0.7Sr0.15Ca0.15Co1-xFexO3-δ为阴极,在氢气/空气中研究了模压法制备的单电池性能,Fe掺杂量对开路电压的高低不起决定性作用,而最高功率密度随Fe掺杂量增加而降低,在650℃最高功率密度由x=0.2时的351.7mW/cm2降为x=0.8时的231.1mW/cm2。

利用溶液前体物组合化学方法研究固相体系相关系

利用溶液前体物组合化学方法研究了La-Ca-Mn-O的相关系。这种合成方法可以完全重现常规固相反应得到的相关系,表明溶液前体物组合化学是一种研究固态相关系的可靠方法。组合化学方法对于提高寻找新型化合物和研究相关系研究效率方面具有重要意义。

Selective hydrogenolysis of furfuryl alcohol to 1,5-and 1,2-pentanediol over Cu-LaCoO_3 catalysts with balanced Cu^O-CoO sites

Selective hydrogenolysis of biomass‐derived furfuryl alcohol(FFA)to 1,5‐and 1,2‐pentanediol(PeD)was conducted over Cu‐LaCoO3 catalysts with different Cu loadings;the catalysts were derived from perovskite structures prepared by a one‐step citrate complexing method.The catalytic performances of the Cu‐LaCoO3 catalysts were found to depend on the Cu loading and pretreatment conditions.The catalyst with 10 wt%Cu loading exhibited the best catalytic performance after prereduction in 5%H2‐95%N2,achieving a high FFA conversion of 100%and selectivity of 55.5%for 1,5‐pentanediol(40.3%)and 1,2‐pentanediol(15.2%)at 413 K and 6 MPa H2.This catalyst could be reused four times without a loss of FFA conversion but it resulted in a slight decrease in pentanediol selectivity.Correlation between the structural changes in the catalysts at different states and the simultaneous variation in the catalytic performance revealed that cooperative catalysis between Cu0 and CoO promoted the hydrogenolysis of FFA to PeDs,especially to 1,5‐PeD,while Co0 promoted the hydrogenation of FFA to tetrahydrofurfuryl alcohol(THFA).Therefore,it is suggested that a synergetic effect between balanced Cu0 and CoO sites plays a critical role in achieving a high yield of PeDs with a high 1,5‐/1,2‐pentanediol selectivity ratio during FFA hydrogenolysis.

Y替代La_(2/3)Ca_(1/3)MnO_3体系的结构与输运行为

系统研究了 (La1 -xYx) 2 3Ca1 3MnO3(0 0≤x≤ 0 3)体系的结构和输运行为 .结果表明 ,实验样品具有很好的单相结构 ,随Y掺杂浓度的增加 ,金属—绝缘体 (M—I)转变温度TMI向低温区移动 ,对应的峰值电阻率 ρp 升高 ,对x =0 3样品 ,较未替代样品 (x=0 0 )增幅达 8个数量级 .在外加磁场下 ,材料表现出很强的磁电阻效应 .同时 ,从实验结果出发 ,直接给出了输运特性与晶体结构之间的关联 ,并从双交换模型和可变程跃迁理论出发 ,对实验结果进行了初步讨论 .