The role of redox property of La2-x(Sr,Th)(x)CuO4 +/-lambda playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La2-xSrxCuO4 +/- lambda (0.0 less than or equal to x less than or equal to 1.0) and La(2-x)Tn(x)CuO(4 +/-) (lambda) (0.0 less than or equal to x less than or equal to 0.4), with K2NiF4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry (lambda) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO + CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, A and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO + CO reaction. For the NO + CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted). (C) 2000 Elsevier Science B.V. All rights reserved.

Recovery of Ce(IV) and Th(IV) from rare earths(III) with Cyanex 923

Solvent extraction of Ce(IV), Th(IV) with Cyanex 923 in n-hexane from sulphuric acid medium was studied with the dependence of the extraction on acidity and temperature being investigated. The Ce(IV) and Th(IV) extraction mechanism was proposed by slope analysis and the IR spectra of purified Cyanex 923 saturated with Ce(IV) were employed to determine the composition of the Ce(IV) complex. The equilibrium constant and thermodynamic functions of Th(IV) extraction were calculated and the characteristics of the stripping of Ce(IV), Th(IV) from the loaded organic phase were studied. (C) 1998 Elsevier Science B.V. All rights reserved.

La_(2-x)(Sr,Th)_xCuO_(4±λ)系催化剂的表征及对CO+NO反应催化性能的研究

合成了x值不同的La2 -xSrxCuO4±λ( 0 .0≤x≤ 0 .1 )和La2 -xThxCuO4±λ( 0 .0≤x≤ 0 .4)两系列K2 NiF4型复合氧化物催化剂 ,用XRD和IR研究了催化剂的晶体结构 .利用化学分析和XPS等方法测定了该系列含Cu氧化物中Cu离子的平均价态、非化学计量氧 (λ)和催化剂的表面和体相组成 .通过控制B位Cu离子的价态和氧化物的非化学计量氧在一定范围内有规律的变化 ,考察对NO +CO反应的催化性能 ;利用MS TPD法研究了该系列氧化物对NO和CO +NO等小分子的吸附和活化性能 ,在此基础上探讨了含Cu的A2 BO4型复合氧化物对NO +CO反应中的催化作用本质 .发现在低温反应条件下 ,NO分子的活化是控制步骤 ,催化剂的活性与低价离子及其含量有关 .在较高反应温度下 ,NO的吸附为控制步骤 ,催化活性与氧空位有关

Perovskite-like mixed oxides La2-x(Sr,Th)(x)CuO4+/-lambda

Two groups of mixed oxides La2-xThxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 0.4) and La2-xSrxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 1.0) were prepared. Their crystal structures were studied with XRD and IR spectra, etc. Meanwhile, the average valence of Cu ions and nonstoichiometric oxygen (lambda) was measured through chemical analyses. Catalysis of the abovementioned mixed oxides was investigated in phenol hydroxylation, good results were obtained for some mixed oxides, and found that the catalysis of these mixed oxides have close relation with their defect structure and composition. A radical substitution mechanism was also proposed for this catalytic reaction.

Characterization and catalytic behavior of La2-x(Sr,Th)(x)CuO4+/-lambda in reaction NO+CO

Two mixed oxide systems La2-xSrxCuO4+/-lambda(0.0 less than or equal to x less than or equal to 1.0) and La2+xThxCuO4+/-lambda(0.0 less than or equal to x less than or equal to 0.4) with K2NiF4 structure were prepared by varying re values; Their crystal structures were studied by means of XRD and IR spectra. The average valence of Cu ion at B site, nonstoichiometric oxygen (A) and the chemical composition in the bulk and on the surface of the catalysts were measured by means of chemical analysis and XPS. The catalytic behavior in reaction CO + NO was investigated under the regular change of average valence of Cu ion at B site and nonstoichiometric oxygen (lambda). Meanwhile, the adsorption and activation of the small molecules NO and the mixture of NO + CO over the mixed oxide catalysts were studied by means of MS-TPD. The catalytic mechanism of reaction NO + CO over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, while at higher temperatures the adsorption of NO is the rate determining step and the catalytic activity is related to the oxygen vacancy and its concentration.

复合氧化物La_(2-x)(Sr,Th)_xCuO_(4±λ)——一种新型的苯酚羟化催化剂

二酚(邻苯二酚,对苯二酚)是重要的化工原料,二酚生产一直是人们所关注的课题,70年代以前主要采用的一些污染严重的生产过程正被逐渐淘汰。目前,利用过氧化氢和苯酚为原料联产邻苯二酚和对苯二酚,在化工生产中占有重要的地位。常见的催化剂有等。但这些催化剂也具有明显的不足之处,前两者具有均相催化反应本身难以克服的缺点,后者虽具有多相催化过程的优点,但由于此类催化剂难以制取,而且此类催化剂主要反应孔道的孔径较小(<0.9 nm),反应物和生成物难以在孔道中扩散,使得反应速度较慢。当前国际上还正在积极寻找新的催化体系以达到高效无污染生产二酚的目的。

Roles of oxygen vacancy and lower valence metallic ion in direct decomposition of NO over La-2-x(Sr,Th)(x)CuO4+/-lambda

Two systems of La2-xSrxCuO4+/-lambda and La2-xThxCuO4+/-lambda, mixed oxides with K2NiF4 structure were synthesized. The compositions and structures of the catalysts were characterized by means of XRD, XPS, chemical analysis and so on. The catalytic behavior for the direct decomposition of NO has been investigated. The results show that the catalytic activity is closely related to the oxygen vacancy and lower valence metallic ion in the direct decomposition of NO. The presence of oxygen vacancy is necessary for mixed oxide to have steady activity in NO decomposition.

SOLVENT-EXTRACTION OF SC(III), ZR(IV), TH(IV), FE(III), AND LU(III) WITH THIOSUBSTITUTED ORGANOPHOSPHINIC ACID EXTRACTANTS

The solvent extraction of Sc(III), Zr(IV), Th(IV), Fe(III) and Lu(III) with Cyanex 302 (bis(2,4,4-trimethylpentyl)monothiophosphinic acid) and Cyanex 301 ( bis(2,4,4-trimethylpentyl) dithiophosphinic acid) in n-hexane from acidic aqueous solutions has been investigated systematically. The effect of equilibrium aqueous acidity on the extraction with these reagents was studied. The separation of Th(IV), Fe(III) and Lu(III) from Sc(III), or the separation of other metals from Lu(III) with Cyanex 302, can be achieved by controlling the aqueous acidity. However, Cyanex 301 exhibited a poor selectivity for the above metals, except for Lu(III). The extraction of these metals with Cyanex 272, Cyanex 302 and Cyanex 301 has been compared. The stripping percentages of Sc(III) for Cyanex 302 and Cyanex 301 in a single stage are near 78% and 75% with 3.5 mol/L and 5.8 mol/L sulphuric acid solutions, respectively. The effects of extractant concentration and temperature on the extraction of Sc(III) were investigated. The stoichiometry of the extraction of Sc(III) with Cyanex 302 was determined. The role of different components of Cyanex 302 in the extraction of Sc(III) was discussed.

La－Th－O系催化剂的结构与甲烷氧化偶联催化性能的关系

研究了Ｌａ－Ｔｈ－Ｏ二元氧化物的组成、结构及其对甲烷氧化偶联反应催化性能的影响；用ＸＲＤ、ＩＲ、ＸＰＳ、ＳＥＭ等方法对催化剂进行表征。Ｌａ－Ｔｈ－Ｏ系列催化剂随Ｌａ／Ｔｈ原子比的变化，可生成Ｌａ＿ｘＴｈ＿（１－ｘ）Ｏ＿（２－δ）固溶体。具有萤石结构的Ｌａ＿ｘＴｈ＿（１－ｘ）Ｏ＿（２－δ）是甲烷氢化偶联反应的主要活性相。

EXTRACTION MECHANISM OF SC(III) AND SEPARATION FROM TH(IV),FE(III) AND LU(III) WITH BIS(2,4,4-TRIMETHYLPENTYL)PHOSPHINIC ACID IN N-HEXANE FROM SULFURIC-ACID-SOLUTIONS

The extraction equilibrium data of sulphuric acid and scandium(III) with bis(2,4,4-trimethylpentyl)phosphinic acid (H[BTMPP]) from sulphuric acid solutions have been obtained. There are two extraction mechanisms of scandium(III) with H[BTMPP] at different

GENERAL ALPHA-N INDEX AND ITS APPLICATION .1. GENERAL ALPHA-N INDEX AND ITS APPLICATION IN THE EXTRACTION OF Y, CE, U, AND TH BY NEUTRAL PHOSPHORUS EXTRACTANCTS

The general a(N) index is established for molecules containing heteroatoms, rings, and multiple bonds. The general a(N) index is able to describe molecules with minute differences in structure and can also reveal the properties of molecules. This theory is successfully applied to the case of neutral phosphorus extractants. Both the molecular polarity and steric effect are characterized by the general a(N) index. The relationships between these properties and the distribution ratios for extracting Y, Ce, U, and Th are also shown by the general a(N) index.

广义α_N指数及其应用——Ⅰ.广义α_N指数及其在中性磷萃取剂萃取Y、Ce、U和Th性能方面的应用

首先引进一般有机化合物的广义a_N指数,该指数能分辨有微小结构差别的有机化合物分子。在此基础上,计算了某些中性磷萃取剂的广义a_N指数。并将其与萃取性能进行相关分析,得到了满意的结果。

Genesis of Th-230 excess in basalts from mid-ocean ridges and ocean islands: Constraints from the global U-series isotope database and major and rare earth element geochemistry

Based on Th-230-U-238 disequilibrium and major element data from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs), this study calculates mantle melting parameters, and thereby investigates the origin of Th-230 excess. (Th-230/U-238) in global MORBs shows a positive correlation with Fe-8, P (o), Na-8, and F-melt (Fe-8 and Na-8 are FeO and Na2O contents respectively after correction for crustal fractionation relative to MgO = 8 wt%, P (o)=pressure of initial melting and F (melt)=degree of melt), while Th-230 excess in OIBs has no obvious correlation with either initial mantle melting depth or the average degree of mantle melting. Furthermore, compared with the MORBs, higher (Th-230/U-238) in OIBs actually corresponds to a lower melting degree. This suggests that the Th-230 excess in MORBs is controlled by mantle melting conditions, while the Th-230 excess in OIBs is more likely related to the deep garnet control. The vast majority of calculated initial melting pressures of MORBs with excess Th-230 are between 1.0 and 2.5 GPa, which is consistent with the conclusion from experiments in recent years that D (U)> D (Th) for Al-clinopyroxene at pressures of > 1.0 GPa. The initial melting pressure of OIBs is 2.2-3.5 GPa (around the spinel-garnet transition zone), with their low excess Ra-226 compared to MORBs also suggesting a deeper mantle source. Accordingly, excess Th-230 in MORBs and OIBs may be formed respectively in the spinel and garnet stability field. In addition, there is no obvious correlation of K2O/TiO2 with (Th-230/U-238) and initial melting pressure (P (o)) of MORBs, so it is proposed that the melting depth producing excess Th-230 does not tap the spinel-garnet transition zone. OIBs and MORBs in both (Th-230/U-238) vs. K2O/TiO2 and (Th-230/U-238) vs. P (o) plots fall in two distinct areas, indicating that the mineral phases which dominate their excess Th-230 are different. Ce/Yb-Ce curves of fast and slow ridge MORBs are similar, while, in comparison, the Ce/Yb-Ce curve for OIBs shows more influence from garnet. The mechanisms generating excess Th-230 in MORBs and OIBs are significantly different, with formation of excess Th-230 in the garnet zone only being suitable for OIBs.

中国北方风成堆积的风化作用与环境变迁—U-Th、~(10)Be及元素地球化学的研究

The surface of the Earth is continuously undergoing changes as a result of weathering-erosion, plate tectonics and volcanic processes. Continental weathering-erosion with its complex rock-water interactions is the central process of global biochemical cycling of elements, and affects the long-term ocean atmosphere budget of carbon dioxide both through the consumption of carbonic acid during silicate weathering and through changes in the weathering and burial rates of organic carbon. Rates of the weathering-erosion depend on a variety of factors, in particular rock properties and chemical composition, climate (especially rainfall), structure, and elevation. They are quite variable on a regional scale. Thus, environmental changes in a region could be indicated by the history of weathering-erosion in the region. Recent attention has focused on increased silicate weathering of tectonically uplifted areas in the India-Asia collision zone as a possible cause for falling atmospheric CO_2 levels in the Cenozoic era. The wind blown dust deposits in the Loess Plateau is derived from the arid and semiarid regions in northwestern China, in turn, where the deposits have been derived from the Qinghai-Xizang Plateau and the high mountains around. Therefore, geochemistry of the wind blown loess-paleosol and red clay sequences may provide insight both to paleoenvironmental changes on the Loess Plateau, and to the uplift and weathering-erosion histories of the Qinghai-Xizang Plateau. In this paper, uranium-thorium series nuclides and cosmogenic ~(10)Be have been employed as tracers of weathering intensities and histories of the dust sediments in the Loess Plateau. Major elements, such as Na, Al, Fe etc., are also used to estimate degree of chemical alteration of the dust sediments and to rebuild the history of weathering on the Loess Plateau. First of all, using a low-level HPGe γ-ray detector, we measured U and Th series nuclides in 170 loess and paleosol samples from five sites in the Loess Plateau, going back 2.6 Ma. The results show that ~(238)U activities are disequilibrium with its daughter nuclide ~(230)Th in young loess-paleosol sequence, indicating that weathering was happened both in dust deposition site and in dust source regions. Using concentrations of ~(238)U and ~(232)Th in the samples, we estimated the amounts of ~(238)U leached out of from paleosols due to weathering. Further, based on analyses of ~(230)Th in paleosols deposited in the past ca. 140 ka, we determined when the paleosols weathered in the source regions. We conclude that most of the weathering in the dust-source regions may have occurred during the interglacials before dust deposition.

碳酸盐岩风化过程中的U－Th不平衡研究－以黔中、黔北为例

为了进一步获得贵州碳酸盐岩风化成土过程的信息，为测定风化成土速率的研究工作奠定基础，本次研究工作通过U－Th的地球化学特征与主量元素、微量元素、稀土元素的地球化学特征的对比研究以及U－Th不平衡来研究贵州两个碳酸盐岩风化剖面的风化成土过程，并得出以下总体认识： 贵州碳酸盐岩风化剖面中的238U－234U－230Th不平衡说明风化剖面中的U－Th不平衡与风化过程密切相关，与风化壳中矿物和铁壳的演化特征密切相关。风化剖面不仅被简单的持续积累或者滤失过程所控制，而且被每一个土层中的复杂的重组过程所影响。U－Th不平衡也说明风化系统的扰动可能与中更新世晚期的气候变化有关。风化剖面中的U－Th不平衡是由母岩碳酸盐岩的风化、风化流体的溶解作用、表土层中的有机质、铁质结核带中的氧化铁矿物以及伊利石、高岭石等粘土矿物对U、Th的吸附作用、α反冲作用以及微生物的还原作用等共同作用的结果。 具体结论如下： （1）两个风化剖面中的U、Th都在半风化层中相对基岩强烈富集，安顺白云岩风化剖面中U、Th在全风化层中下部富集；而遵义石灰岩风化剖面中的U在全风化层中部富集，Th在全风化层上部富集，然后向表土层逐渐减少。 （2）U、Th在半风化层中相对基岩强烈富集，是因为在半风化层中，基岩中的原生矿物发生溶解、蚀变，生成新的次生粘土矿物伊利石，而伊利石对U、Th具有强烈的吸附能力。风化剖面中U、Th的富集主要与地表水的淋滤作用以及铁壳在进一步的风化过程中溶解释放出其中所富集的U、Th，而U、Th向下重新迁移的过程有关。 （3）风化剖面中U、Th的分布特征说明U、Th的含量与风化过程密切相关，与风化壳中的矿物和铁壳的演化特征密切相关。遵义石灰岩风化剖面中U、Th的淋失程度比安顺白云岩风化剖面中U、Th的淋失程度弱也说明了遵义石灰岩风化剖面的风化程度要低于安顺白云岩风化剖面的风化程度。 （4）安顺白云岩风化剖面中，234U/238U在<1和＞1之间交替变化。除在剖面中部，230Th/238U≈1外，230Th/238U基本上都＞1。 （5）安顺白云岩风化剖面中的238U －234U－230Th不平衡表明：安顺白云岩风化剖面中的U－Th不平衡是母岩碳酸盐岩的风化、风化流体的溶解作用、表土层中的有机质、铁质结核带中的氧化铁矿物以及伊利石、高岭石等粘土矿物对234U、230Th的吸附作用、α反冲作用以及微生物的还原作用等共同作用的结果。 （6）遵义石灰岩风化剖面中234U/238U除少数几个点外，大多数采样点的234U/238U都＜1。除了少数几个点外，大部分230Th/238U＞1。 （7）遵义石灰岩风化剖面中的238U －234U－230Th不平衡表明：234U－238U不平衡主要是由地表水和入渗水的溶解作用以及α反冲作用为主要的控制机制。而风化剖面中230Th－238U不平衡主要是由表土层中的有机质、高岭石、氧化铁矿物以及伊利石对230Th吸附作用和α反冲作用共同作用的结果。 （8）将U的迁移模型应用于本研究中的两个碳酸盐岩风化剖面，说明这两个风化剖面都被U的近期积累或者滤失过程所影响，风化系统处于过渡的不稳定状态，并通过U在风化剖面中的重新迁移将系统带回稳定状态。 （9）由等时线定年法计算出的安顺白云岩风化剖面的年龄范围为：87.0±7.8－479.2±47.9ka；遵义石灰岩风化剖面的年龄范围为：62.3±8.7－353.3±31.8ka。 （10）由等时线定年法可知：两个风化系统将在～1.1Ma达到稳定状态。 （11）碳酸盐岩风化剖面应用U的迁移模型得出的U的迁移过程与风化剖面中主量元素和微量元素的迁移特征相吻合，说明模型的选择是正确的。 （12）整个风化剖面的238U－234U－230Th不平衡说明风化剖面中的U－Th不平衡与风化过程密切相关，与风化壳中矿物和铁壳的演化特征密切相关。风化系统的扰动可能与中更新世晚期的气候变化有关。碳酸盐岩风化剖面被U的近期迁移过程所影响，风化剖面中的每一个单元甚至每一个土样都具有复杂的历史。这些单元或者土样是古老的风化历史和近期的重新迁移过程的叠加。