Pd-Au/SiO2: Characterization and Catalytic Activity
Pd-Au/SiO2: Characterization and Catalytic Activity
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Pd-Au/SiO2：表征和催化活性
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
J. Sobczak
中科院分区：
文献类型：
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作者：
W. Juszczyk;Z. Karpiński;D. Lomot;J. Pielaszek;J. Sobczak
摘要/ Abstract摘要：以二氧化硅为初始湿共浸渍剂，在空气中煅烧，在380℃下氢气还原15 h，制备了一系列Pd-Au/ sio2催化剂。采用多种技术，氢气和一氧化碳的化学吸附，程序升温还原，x射线衍射，x射线光电子能谱，以及作为催化探针的新丁烷转化，表征了金属的分散和两种金属构件与支架之间的相互作用。研究发现，制备的材料并不均匀：金属分散度很高的富钯相（粒径约1.3 nm）与分散度低得多的富金相（粒径约15 nm）共存。x射线光电子能谱显示，在还原硅负载的钯金催化剂中存在一定量的硅物质（如还原硅或前硅化钯）。由于Si的含量与金属的分散性呈正相关，这表明这些物质靠近高度分散的Pd（富Pd）材料，在金属和载体之间形成了一种“化学胶”。与其他钯基体系（例如，钯铜和钯锌）相比，二氧化硅与钯和金氯化物的水溶液共浸渍不能产生均匀的双金属材料。
Abstract A series of Pd-Au/SiO 2 catalysts was prepared by incipient wetness coimpregnation of silica with respective chloride solutions, followed by calcination in air and reduction in hydrogen at 380°C for 15 h. A variety of techniques, chemisorption of hydrogen and carbon monoxide, temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and neopentane conversion as a catalytic probe, were employed to characterize metal dispersion and interaction between two metal components and the support. It has been discovered that the prepared materials are not uniform: a palladium-rich phase of very high metal dispersion (particle size ∼ 1.3 nm) coexists with much less dispersed gold-rich phase (particle size ∼ 15 nm). X-ray photoelectron spectroscopy revealed some presence of Si species (as reduced silicon or ex-palladium silicide) in reduced silica-supported Pd-Au catalysts. Because the amount of Si positively correlates with metal dispersion it is suggested that these species are in a close vicinity to the highly dispersed Pd (Pd-rich) material, forming a kind of "chemical glue" between metal and support. In contrast to other Pd-based systems (e.g., Pd-Cu and Pd-Zn), coimpregnation of silica with aqueous solutions of palladium and gold chlorides does not produce well-homogenized bimetallic material.