ⅡB族元素氧化物与γ-Al_2O_3相互作用的XRD研究

我们已经报道过许多离子型或分子型化合物在载体表面有自发分散倾向,并应用X光衍射(XRD)相定量外推法测定活性组分在载体表面最大分散量(阈值)。本文研究元素周期表第二付族(ⅡB)元素(锌、镉、汞)的氧化物与载体γ-Al_2O_3的相互作用情况。结果表明用γ-Al_2O_3浸渍锌、镉、汞的硝酸盐溶液,干燥后硝酸盐热分解生成氧化物,焙烧活化后和氧化铝的相互作用,这三个体系各何不同的特点。     

某些催化剂活性组份在载体表面分散的自发倾向

实验发现许多离子晶体或分子晶体物质与高比表面载体混合后,在低于这些晶体熔点的适当温度下烘烤,这些晶体物质可在载体表面自发分散。烘烤前的X光衍射图有这些晶体的特征峰,烘烤后这些峰变矮以致完全消失。其原因是这些离子或分子与载体表面离子或基团有较强结合力,足以克服这些晶体内部的结合力,使它们分散成表面层相。 对于催化剂的活性组份如果不是金属而是化合物(盐类、氧化物等),其含量又不足在载体表面敷满单层时,常常是以单层分散的方式存在。 本文所得结果,为过去难以进行研究的固-固吸附领域,提供了一种较有效的研究方法和一些基本观点。     

X光衍射相定量外推法测定活性组分在载体表面的分散阈值

活性组分与载体的相互作用,活性组分在载体表面分散的结构状态,以及活性组分在载体表面的最大分散量(分散阈值)是多相催化剂研究中的基本问题。活性组分在载体表面的分散状态和分散阈值取决于活性组分和载体本身的结构和性质。活性组分在载体表面的分散,总是在载体表面能量上和几何上有利的位置进     

非水溶液浸渍法制备TiO2—Al2O3

二氧化钛用作石油炼制的加氢脱硫(HDS)或加氢脱氮(HDN)催化剂载体具有高的活性,其缺点是比表面小,机械强度差。为克服这些缺点,近年来研究了用共胶法、浸渍法和交替成胶法制备TiO_2-Al_2O_3载体。本文报道了以TiCl_4的CCl_4溶液作浸渍液,制备单层覆盖型TiO_2-Al_2O_3载体,并用多晶X光衍射(XRD)、X光光电子能谱(XPS)、透射电子显微镜(TEM)和选区电子衍射(HEED)等实验技术进行了表征。     

用ISS研究负载型催化剂中活性组分与载体间的相互作用

用惰性离子作射体与固体表面原子相互作用,在低能区(0.5～3keV),一般认为,主要是弹性碰撞。由电子云交迭所产生的电子效应往往可以忽略,或者说这类非弹性碰撞效应与弹性碰撞能量损失相比往往很小,实验上的能量分辨不足以探测这类非弹性效应即电子效应。本文选择氧化物和卤化物负载型催化剂体系并从实验上采取了一些方法,使由于电子效应而引起的散射惰性离子的能量损失可以得到分辨。众所周知,电子效应与化学键力密切相关。有人虽曾对由于电子效应等而引起被测元素原子的“质量”变化提出过“有效质量”的概念,但未发表过有关化学方面的工作。本文对MoO_3/TiO_2,MoO_3/γ-Al_2O_3,MoO_3/SiO_2,CuO/γ-Al_2O_3,CuCl/γ-Al_2O_3等催化剂体系进行了研究,发现由于电子效应而     

ⅡB族元素氧化物与γ-Al2O3相互作用的XRD研究

The interaction between γ-Al_2O_3 and the oxides of Zinc, Cadium and Mercury have been studied by x-ray diffraetion(XRD). Samples of ZnO/γ-Al_2O_3, CdO/γ-Al_2O_3 and HgO/γ-Al_2O_3 were prepared by impregnating γ-Al_2O_3 with the corresponding nitrate solutions, then drying and ealeinating. It has been shown that CdO and HgO can be dispersed on γ-Al_2O_3 surface to form submonolayers. Their dispersion capaeieies derived from Fig.2 and Fig.3 are 0.48g CdO/g γ-Al_2O_3 and 0.16g HgO/g γ-Al_2O_3, or 0.20g CdO/100m~2 and 0.067g HgO/100m~2 surface of γ-Al_2O_3 (specific surface of γ-Al_2O_3 is 240m~2/g). On the other hand, ZnO/γ-Al_2O_3 system can not be in a monolayer dispersion state, because ZnO can react with γ-Al_2O_3 to form Zinc spinel at rather low temperature (200 ℃). The difference between these three systems may be attributed to their different ion radius.     

NiO的单层分散态及其载体效应

The NiO dispersion phase on three different supports have been studied by EXAFS in combination with XRD quantitative phase analysis. The result of XRD shows the threshold of NiO/γ-Al_2O_3 system is larger than that of NiO/TiO_2 system and the threshold of NiO/SiO_2 system is the least. From the FT functions of EXAFS for samples we can find that in NiO/γ-Al_2O_3 system a part of Ni changes its coordination polyhedra into tetrahedra, the Ni-Ni coordination peaks reduce markedly with the decrease of NiO content in samples. The result of EXAFS fitting and phase isolation shows Ni-Ni coordination number increases with the increase of NiO content in samples of NiO/γ-Al_2O_3 system and reaches a maximum value of 4.0 and remains constant when NiO content reaches the threshold obtained by XRD. It shows the structure of NiO dispersion phase is in better agreement with the NiO monolayer dispersion model than any other models.
In FT functions of EXAFS for samples at thresholds of two systems the Ni-Ni coordination peaks of NiO/TiO_2 system is much lower than those of NiO/γ-Al_2O_3 system. But they are similar when their NiO contents both close to the threshold of NiO/TiO_2 system. It shows that though the dispersion capacity of NiO in NiO/TiO_2 system is less than that in NiO/γ-Al_2O_3 system its dispersion performance is better.
In NiO/SiO_2 system the coordination peaks are similar to those of pure NiO and the Ni-Ni coordination number approaches 12 of the pure NiO. It shows it is difficult for NiO to disperse on the surface of SiO_2. In fact, for the NiO/SiO_2 system the threshold obtained by XRD is beyond the experiment accuracy so there is no threshold for this system.
Therefore above facts indicate that dispersion threshold and reducing of metal-metal coordination number of the dispersion phase is a quite characteristic feature of monolayer dispersion state.     

MoO3在γ—Al2O3表面分散过程的动力学研究

采用原位X-光衍射仪对MoO_3在γ—Al_2O_3表面上的分散过程进行动力学研究。测定了不同温度下的MoO_3分散量随时间的变化。认为分散过程对于表面有效位置是一级反应,并得到了不同温度下的速率常数和分散过程的活化能。     

嵌入Y型分子筛中钯簇合成与结构的研究

经微波交换-焙烧-氢还原等过程制备了嵌入Y型分子筛中的钯簇化合物（Pd0Y）应用径向电子分布函数法（RedialElectronDistributionFunction），就其钯原子簇化合物进行了结构的研究．结果说明，嵌入Y型分子筛中的钯原子以A1型密堆积方式排列，聚集成约12大小的原子簇，嵌在Y型分子筛超笼之中．分子筛骨架的作用使族之间分立存在．它在超笼之中的占有率仅为0.06因此Pd0Y化合物既有纳米级金属钯的性能，又有分子筛固有的孔道结构特征．如此含有钯簇的分子筛化合物对一氧化碳完全氧化的反应具有超常的催化活性．