用正电子湮没谱学研究氯化稀土在NaY沸石上的分散

用正电子湮没谱学研究氯化富铈稀土与NaY沸石机械混合形成的稀土NaY沸石(RE-NaY)中,氯化稀土在NaY中的分散．分别测量不同质量比的RE-NaY(1％-20％)经500℃烘烤1h,RE-NaY(5％)经过不同温度烘烤1h,以及RE-NaY(5％)经500℃烘烤不同时间后的正电子寿命谱．所有寿命谱都出现了5个寿命分量,其中第3,4,5寿命分别与β笼、超笼及沸石微粒界面空洞的大小和数量相关．实验表明了正电子湮没谱学能敏感地表征氯化稀土在NaY中的分散．     

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱,得到了四个寿命组份,并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化,而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响,但随着质子酸浓度增加,o-Ps在沸石内表面湮没的几率大于笼内,故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系,以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱, 得到了四个寿命组份, 并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化, 而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响, 但随着质子酸浓度增加, o-Ps在沸石内表面湮没的几率大于笼内, 故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系, 以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

正电子湮没与沸石内静电场

本文测定了不同类型沸石的正电子寿命谱。发现o-Ps的湮没寿命, 与沸石静电场之间有良好的对应关系, 静电场愈强, 湮没寿命愈短。根据正电子寿命谱结果。含不同阳离子的Y沸石的静电场强弱次序为KY相似文献   

NaY沸石超笼中合成12-钼磷杂多酸

针对负载杂多酸催化剂在极性反应体系中活性组分易溶脱的难题, 用“瓶中造船(ship in the bottle)”的方法在NaY沸石超笼中合成了12-钼磷酸. 将机械混和的MoO₃晶体和NaY沸石在高温下焙烧, 使MoO₃在沸石表面高度分散, 以此复合物在磷酸水溶液中反应, 得到的固体样品用X射线衍射仪(XRD)、³¹P核磁共振谱(³¹P NMR)和红外光谱(IR)进行了表征, 并测试了其在醋酸和正丁醇的酯化反应中的催化性能. 结果表明, MoO₃质量分数为10%的MoO₃/NaY 中载体仍保持Y沸石的结构, 以此为原料合成的样品呈现出Keggin结构杂多酸的红外特征峰, 并且在核磁共振磷谱中杂多酸的化学位移峰向负值方向发生了较大程度的位移, 说明杂多阴离子与Y沸石羟基发生了强相互作用, 样品在醋酸与正丁醇的酯化反应中显示出了较高的催化活性和优异的重复使用性能. 这些充分说明在NaY沸石超笼中成功合成了12-钼磷酸.     

α-Fe2O3在Y沸石上的分散

用草酸高铁铵浸渍NaY沸石, 并在高温下焙烧, 得到α-Fe_2O_3/NaY沸石体系。经XRD相定量外推法测定, α-Fe_2O_3在NaY沸石上的最大分散量为0.060 gα-Fe_2O_3/gNaY, 仅占α-Fe_2O_3在沸石表面密置单层量的5.5%。首次尝试用正电子寿命谱方法测定α-Fe_2O_3在沸石表面的最大分散量, 所得结果与XRD方法完全吻合。由程序升温还原方法发现沸石上α-Fe_2O_3的还原分两步进行, α-Fe_2O_3先还原成Fe_3O_4, 然后再还原成金属。α-Fe_2O_3分散相与沸石之间的强相互作用, 使这两个还原反应受到阻抑。     

聚对苯二甲酸乙二酯中正电子湮没寿命参数温度效应的研究

对聚对苯二甲酸乙二酯的非晶、低温热处理(54℃)、高温热处理(180℃)以及双轴拉伸等四种不同试样,测量了室温到180℃范围内不同温度在的正电子湮没寿命谱.根据最小二乘曲线拟合解谱结果,可知最长寿命成份的湮没参数τ和I的温度曲线分别灵敏地反映了聚对苯二甲酸乙二酯的玻璃转变过程和结晶过程.据此讨论了正电子湮没寿命参数与PET转变的关联以及PET玻璃转变的有关性质.     

用正电子素探测叶绿素三线激发态浓度的变化

测量了在不同光强下叶绿素环已烷溶液(77 K)和酒精溶液(296 K)的正电子湮没寿命谱。提出正电子素光磁湮没模型以解释实验事实。在77 K固化的叶绿素环已烷溶液中, 正电子湮没寿命谱长寿命组分的湮没参数I_2和Λ_2随光强变化而呈现规律性变化, 表明可利用正电子素光磁猝灭效应来追踪光敏剂分子三线激发态浓度的变化。     

超声法合成3,4-二氢嘧啶-2(1H)-酮衍生物

以取代芳醛（1a~1h）,乙酰乙酸乙酯(2)和脲(3)为原料,MMT/CuCl₂为催化剂,乙醇为溶剂,在超声条件下经Beginelli反应合成了8个3,4-二氢嘧啶-2(1H)-酮衍生物（4a~4h）,其结构经¹H NMR和IR确证。以4a为例,分别采用单因素法和正交实验法研究了催化剂、溶剂、反应温度、超声时间和物料比r［n(1a): n(2) :n(3)］对4a产率的影响。结果表明：在最优反应条件(1a 2.4 mol, r=1.2 : 1.0 : 1.0, MMT/CuCl₂20 mol%, EtOH 1 mL,于90 ℃超声15 min)下,4a产率88.4%。 MMT/CuCl₂循环使用3次,产率基本不变。     

水热条件下Y型沸石的转晶行为

系统研究了以KOH为结构导向剂,Y型沸石（HY和NaY）在水热条件下转晶为MER型沸石的行为.MER型沸石是硅铝比（Si/Al）在2~3之间且具有四种尺寸8元环孔道（3.1Å×3.5Å,2.7Å×3.6Å,3.4Å×5.1Å,3.3Å×3.3Å）的硅铝沸石分子筛,在小分子催化以及分离方面具有重要的潜在应用.传统水热法合成高结晶度MER型沸石需要7~10 d,将Y型沸石置于KOH的溶液中,经水热处理可在2 d内生成高结晶度的MER型沸石,而水热处理具有等价摩尔组成的无定形硅铝凝胶则得不到高结晶度MER型沸石的纯相.HY沸石可在100和150℃发生转晶,而NaY则只能在150℃发生转晶.KOH/SiO₂比和H₂O/SiO₂比对Y型沸石的转晶行为有重大的影响,只有在最优KOH/SiO₂比和H₂O/SiO₂比条件下才能生成高结晶度的MER型沸石.该转晶合成法显著缩短了MER型沸石的合成周期,对缩短其它有重大工业应用价值的沸石分子筛的合成周期有重要的借鉴意义.     

Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external ²²Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by ²²Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.     

预吸附微波合成纳米NaY沸石晶种制备NaY型分子筛膜

在常压回流的微波加热体系中成功地合成出纳米尺寸的NaY分子筛,XRD和SEM等表征结果表明,分子筛具有40nm左右的平均晶粒尺寸.以其为晶种,预吸附在多孔氧化铝载体上,结合原位水热法进行二次晶化,制备出较为致密的NaY分子筛膜,该膜主要以孪生聚晶的形式存在.CO₂/N₂气体分离测试结果显示,随着温度的升高,分子筛膜的气体分离能力呈上升趋势,在140℃时真实选择分离系数达到最大值4.0.     

Positronium as a tool to monitor changes of chemical structure

The applicability of positron annihilation spectroscopy for chemical structural problems is demonstrated by two examples: For the swelling dynamics of an amphiphilic polymer network, very quick structural changes were indicated by positronium lifetime parameters at very low swelling ratios and a hydration mechanism was proposed accordingly. For the series [Fe_xZn_1−x(propyltetrazole)₆](BF₄)₂(x=1, 0.6, 0.4, 0.1, 0), changes in the dynamic structure were revealed by positronium lifetime spectroscopy. For compounds of x>0, temperature-induced spin-crossover was detected.     

用正电子谱学研究USY沸石中二次孔的脱水

超稳Ｙ型沸石（ＵＳＹ）分子筛是石油催化裂化中的优异催化剂,它是由ＨＹ型沸石经高温水热处理制备的,它的特点之一是具有良好的热稳定性．因而,对ＵＳＹ的改性研究一直受到关注［１-５］,尤其是在制备ＵＳＹ过程中由于水热处理所产生大量二次孔,它与ＵＳＹ的结构与?..     

Radiation effect on positronium formation in low-temperature polyethylene

The irradiation effect of γ-rays on polyethylene (PE) has been studied by positron annihilation lifetime spectroscopy (PALS). In the case of non-irradiated PE samples, at a low temperature below the glass-transition temperature, the intensity of the long-lived component of positronium, I₃, increases due to an increase in the concentration of trapped electrons. However, the increase in I₃ obtained in a few MGy γ-irradiated samples became very small due to the effect of induced radicals. It has been observed that the trapped electrons were affected by the intensity of the positron sources used for a PALS experiment.     

Cu+/SiO2-ZrO2催化剂的制备及其催化甲醇氧化羰基化性能

采用溶胶-凝胶法制备了SiO₂-ZrO₂复合氧化物载体,通过和CuCl₂进行离子交换制备了Cu⁺/SiO₂-ZrO₂催化剂,并研究其催化甲醇液相氧化羰基化合成碳酸二甲酯性能。结果表明,Zr以离子形式进入无定型SiO₂骨架结构中形成Si－O－Zr键,同时产生较强的B酸中心。CuCl₂通过热处理自还原为CuCl分散在SiO₂-ZrO₂载体表面,并与载体表面B酸发生离子交换形成Cu⁺物种,从而保留了活性金属组分Cu,脱除大部分的Cl元素,改善催化剂失活和设备腐蚀等问题。当焙烧温度为450℃时,催化剂表现出良好的催化活性,CH₃OH转化率、DMC选择性和时空收率分别达到10.0%、79.4%和1.45g/(g·h)。
     

Application of positron annihilation technique to reverse osmosis membrane materials

Positron annihilation lifetime spectroscopy has been adopted as a new approach for studying vacancies of reverse osmosis membrane materials composed of cellulose acetate films and aromatic polyamide resins. The intensity of the ortho-positronium (o-Ps) lifetime increased with the amount of vacancies determined using N₂ isotherm at −195°C. Changes of vacancy profiles induced by heat treatment in the cellulose acetate films were detected using o-Ps. It was found that the positron annihilation technique is applicable to the study of vacancy profiles associated with salt selectivity in typical reverse osmosis membranes.     

CO2 absorption of perovskites as seen by positron lifetime spectroscopy

The CO₂ absorption of several ABO₃ type perovskites was studied by positron lifetime spectroscopy. The longer positron lifetime was associated with positrons trapped by A site vacancies. The evaluated positron lifetime data indicated the relative stability of the crystal structure of Sr(Co_0.5Fe_0.5)O_3−δ against Ca doping at low Ca concentrations. Oxygen desorption and CO₂ absorption/desorption could also be followed by positron lifetime spectroscopy. It was shown that the concentration of oxygen vacancies has a large effect on positron lifetime data through the electron density of A site vacancies.