嵌入Y型分子筛中钯簇合成与结构的研究

Pd clusters encaged in Y-zeolite (Pd0Y) have been prepared by means of exchanging zeolite HY with [Pd(NH3)4]2+ under microwave radiation. The product formed was deaminized by heating, washed sufficiently with de-ionized water and reduced with hydrogen. The crystal phase diffraction of Pd was not found in the XRD spectrogram of Pd0y. According to polycrystal X-ray diffraction data. Radial Electron Distribution Function (REDF) of Pd0Y was calculated to elucidate the structure of Pd cluster. The results show that the Pd clusters are of the Al type closely packed arrangement. The dimension of them is about 12 Å. They are encaged in the supercage of zeolite Y. Their occupancy on the supercage is as small as 0.06 so that the framework structure of zeolite Y is unchanged. Therefore, the high dispersing Pd cluster aggregating in supercage exhibit strong catalytic effect. The CO-conversion of Pd0Y with Pd 0.72% and 6.13% (in mass fraction) is 67 % and 100 % (in volume fraction) respectively. Evaluation conditions:
mixed gas containing 0.02% CO and air,
space velocity 3000 h-1,
reaction temperature 0 ℃.     

SPONTANEOUS DISPERSION OF SOME ACTIVE COMPONENTS ONTO THE SURFACES OF CARRIERS

If an ionic or molecular crystalline solid is mixed with a carrier of high specific surface and then heated at a suitable temperature below its melting point for several hours, the crystalline solid will disperse spontaneously onto the surface of the carrier. It has been proved by the fact that the X-ray diffraction peaks of the crystalline phase either diminish sharply or disappear completely according as whether the amount of the solid mixed with each unit weight of carrier exceeds the critical amount or not and this critical amount of solid is closely related to and usually varies directly as the specific surface of the carrier.If the active component of a catalyst is a compound instead of a metal, and its quantity is not enough to cover the surface of the carrier, it often disperses somewhat as a monolayer, because the ions or molecules of the active component combine strongly with the surface ions or groups of the carrier. This paper presents some fundamental points and methods of investigation in     

CrO3在γ-Al2O3和SiO2载体表面的分散状态

用X光衍射(XRD)方法研究了CrO_3/SiO_2和CrO_3/γ-Al_2O_3体系。用相定量外推法测定活性组份在载体表面的最大分散量。在干燥气氛中将CrO_3与载体混合, 并在低于CrO_3熔点的温度下烘烤制备样品, 实验得到CrO_3在SiO_2或者γ-Al_2O_3表面的最大分散量都随温度的升高而增大。CrO_3在SiO_2表面的最大分散量由101 ℃的0.27gCrO_3/g SiO_2到170 ℃的0.38g CrO_3/g SiO_2; CrO_3在γ-Al_2O_3表面的最大分散量由120 ℃的0.22g CrO_3/g γ-Al_2O_3到171 ℃的0.42g CrO_3/g γ-Al_2O_3。CrO_3在SiO_2或γ-Al_2O_3表面的最大分散量超过密置单层量, 可由易聚合形成同多酸根来解释。     

CO2对Cu-Ce-O催化剂催化氧化CO活性的影响

用CO作为探针研究CeO。的表面性质,以及研究CO和CO。与CeO。的相互作用,已有不少报导［‘－’1．Br。ysse等人发现CO在CeO。上的吸附,总伴随着催化剂的还原和COZ的生成;CO。在CeO。上的吸附不总是可逆的,CO。的存在会降低其对CO的催化氧化活性,对反应有抑制的影响,甚至会使表面中毒问．也有报导在CO或COZ气氛下,有证据表明CeO。有不利干活性的碳酸盐物种形成;反应中生成的C（）。也可能吸附在表面上形成稳定的碳酸盐,从而抑制反应的继续进行k‘］．＊0。对O;－O－（）催化剂在催化氧化以）中的影响报导比较少问．…     

APPLICATION OF XPS TO STUDYING DISPERSION AND SURFACE STATE FOR MoO_3 SUPPORTED ON THE SURFACE OF TiO_2, γ-Al_2O_3 AND SiO_2

In MoO_3/TiO_2, MoO_3/γ-Al 2O_3 and MoO_3/SiO_2 systems, the relationships between I_(Mo3d)/I_(Ti2p), I_(Mo3d)/I_(Al2p), I_(Mo3d)/I_(Si2p) and added amount of MoO_3(g/g carrier) were studied by XPS. Experiments showed that all the curves obtained had a turning point each, corresponding to the monolayer dispersion threshold by XRD in our previous paper. This means that both methods are successful for studying the maximum dispersion amount and surface state of supported metal oxides (or salts) catalysts. Although the two methods are not from the same principle, they are verifiable and complementary to cach other in studying dispersion problems.     

WO3在γ-Al2O3表面的分散状态和最大分散量

应用X光衍射法(XRD)测定了WO2/γ-Al2O3体系的物相组成和平均晶粒度,以及该体系的孔容和比表面:应用XRD相定量外推法和光电子能谱(XPS)峰强度比(Iw4f/IA12s)法定量测定了WO3在γ-Al2O3表面的最大分散量,测值分别为0.21和0.20gWO3/100m[2]γ-Al2O3,与按照WO3在γ-Al2O3表面作密置单层排布模型的计算值0.189WO3/100m[2],即4.9x10[18]W原子/m[2])相近,对WO3/γ-Al2O3体系与MoO3/γ-Al2O3体系比较和讨论。     

MoO3在不同来源的γ-Al2O3表面单层分散的研究

MoO_3与不同制备方法和来源的γ-Al_2O_3(包括η-Al_2O_3)干混、焙烧制备的样品,或者用浸渍、焙烧制备的样品,通过X光衍射测得的MoO_3最大分散量都与按密置单层模型计算得到的结果(每100米~2γ-Al_2O_3表面0.117克MoO_3,即4.9×10~(18)Mo原子/米~2)相近。这样可以通过X光衍射测定MoO_3在每克γ-Al_2O_3上的最大分散量而得到γ-Al_2O_3的比表面。比表面和孔容的研究结果也支持MoO_3在γ-Al_2O_3表面呈密置单层分散的模型。     

NiO在TiO2载体表面的分散状态

采用X-光多晶衍射、透射电子显微镜、选区电子衍射、X-光光电子能谱、俄歇电子能谱等实验方法研究了NiO/TiO_2体系,表明NiO在低载量范围内以单层形式分散在载体TiO_2表面,当NiO的载量超过一定限度时,则除了单层分散之外,还出现多余的晶相NiO.XRD相定量外推法测定得到NiO在TiO_2表面的最大分散量(分散阈值)为0.097g NiO/100m~2TiO_2,XPS和AES峰强度比的测定得到与以上描述相吻合的结果.     

应用XPS研究MoO_3在TiO_2,λ-Al_2O_3和SiO_2等载体表面上的分散量和表面状态

本文应用XPS法测定了MoO_3/TiO_2,MoO_3/γ-Al_2O_3和MoO_3/SiO_2等体系的I_(Mo3d)/I_(Ti2p),I_(Mo3d)/I_(Al2p),I_(Mo3d)/I_(Si2p)随MoO_3加入量(g/g载体)递变的关系。测定结果表明MoO_3在这几种载体上都有一分散阈值,阈值前MoO_3在载体上呈单层分散,阈值后剩余的MoO_3以晶粒形式分布在载体上。这些结果都与X射线相定量外推所得的结果吻合良好。说明这两种方法在研究氧化物负载型催化剂的分散量和表面状态上都是有效的。