Abstract
Novel in-situ reduction approach was applied for the synthesis of palladium nanoparticles in the pores of mesoporous silica materials with grafted siliconhydride groups. Matrices possessing different structural properties (MCM-41, SBA-15 and Silochrom) were used. Samples were studied by nitrogen adsorption-desorption method, low-angle X-ray diffraction, transmission electron microscopy (TEM) and FT-IR/PAS spectroscopy. The temperature-programmed oxidation (TPO) and reduction (TPR) methods were applied to examine reducibility of palladium species. Palladium containing catalysts were tested in methane oxidation reaction. It was demonstrated that relatively large pores in SBA-15 type silica facilitated formation of well-dispersed palladium nanoparticles confined in the pores channels. In the case of MCM-41 support, metallic palladium nanoparticles were formed on the external surface. The obtained materials showed high catalytic activity. Lower activity of the samples containing small crystallites located in the pore volume at high temperatures was related to worse accessibility of active sites to the reation mixture.
Highlights
Metal nanoparticles have attracted considerable attention in modern technology
It was demonstrated that relatively large pores in SBA-15 type silica facilitated formation of well-dispersed palladium nanoparticles confined in the pores channels
In the temperature-programmed oxidation (TPO) analysis, the sample was introduced to the quartz flow reactor, the temperature of the reactor was increased with the rate 10 ̊C/min
Summary
Metal nanoparticles have attracted considerable attention in modern technology. The emerging physicochemical properties of materials are often observed when the particle size reaches nanometer range [1]. Immobilization of groups possessing pronounced reducing properties on the surface of silica allow one to solve the problem of nanoparticles sintering. In this case, formation of nanoparticles on the silica surface occurs due to reduction of metal ions immediately in a place of reducer attachment [10]. Reduction process is caused by properties of surface silicon hydride groups, accompanied by their hydrolysis and formation of high-disperse metal particles of nanometer size [11,12]. Obtaining metal nanoparticles immediately in the place of reducer attachment Another consists in application of ordered mesoporous silicas as supports confining palladium nanoparticles and preventing particles aggregation. Especially palladium, placed on the supports with large specific surface areas and good thermal stability, demonstrated the highest activity for complete oxidation of methane among other [17,18]
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