Preparation Of Noble Metal/inorganic Porous Supports Nanocomposite Particles And Their Catalytic Property

Noble metal nanoparticles(NPs), such as Au, Ag, Pt and Pd NPs, have attracted wide attention owing to their excellent optical and catalytic properties. However,noble metal NPs are inclined to undergo agglomeration due to their small size, large surface area and surface energy. The agglomeration of noble metal NPs leads to a serious deterioration of their catalytic activity. The dispersion and catalytic properties of noble metal NPs may be improved through immobilization of noble metal NPs on a porous inorganic nano-support. The catalytic activity of supported noble metal nanocatalysts is closely related to the type of noble metal, the particle size and morphology of noble metal NPs, as well as the type, size, and pore structure of inorganic nano-supports. The preparation of supported noble metal nanocatalysts with a high catalytic property through a convenient and scalable technique is still a challenging work. In this thesis, a new technique for the preparation of noble metal/inorganic porous supports nanocomposite particles(NCPs) through a combination of the sol–gel process in inverse miniemulsions and in situ reduction of the incorporated noble metal salts was proposed. The preparation process, structure and catalytic properties of the noble metal/inorganic porous supports NCPs were systematically investigated.AgBF4/TiO2 NCPs were firstly prepared through a sol–gel process of titanium ethoxide in inverse miniemulsions with the polar solution of AgBF4 as droplets. The incorporated sliver salts were reduced on the surface of the TiO2 nanosupports to obtain Ag/TiO2 NCPs. The results of transmission and scanning electron microscopy showed that the Ag/TiO2 NCPs were spherical particles and Ag NPs were mainly distributed onto the surface of the NCPs which is very suitable for the catalytic applications. The as-syntehsized TiO2 nano-supports were amorphous, but they could be changed to anatase TiO2 through calcination at 400°C. The Ag content of NCPs could be conveniently adjusted by the AgBF4 loading. With the increasing of AgBF4 loading, the particle size of Ag/TiO2 NCPs only varied in the range of 100~140 nm,and in addition, the specific surface area of the TiO2 nano-supports decreased. Thephotodegradation of Rhodamine B was selected as the model reaction to evaluate the visible light catalytic activity of the Ag/TiO2 NCPs. The results indicate that the Ag/amorphous TiO2 NCPs and the Ag/anatase TiO2 NCPs have a high visible light catalytic activity. In addition, with the increase of the Ag conent, the catalytic activity of the Ag/anatase TiO2 NCPs increased first, and then slightly decreased.HAuCl4/SiO2 NCPs were prepared through a sol–gel process of tetraethyl orthosilicate in inverse miniemulsions with the polar solution of HAuCl4 as droplets.The incorporated gold salts were reduced on the surface of the SiO2 nanosupports to obtain Au/SiO2 NCPs. The Au NPs were mainly distributed onto the surface of the SiO2 nano-supports. With the increase of the HAuCl4 loading from 0.043 g to 0.17 g,the particle size of the Au/SiO2 NCPs decreased first and then remained constant, the particle size of Au NPs increased from 10 nm to 18 nm. The isotherms of the SiO2nano-supports with various HAuCl4 loadings were I–B type isotherm, indicating the presence of microporous structures. The specific surface areas of the Si O2nano-supports with various HAuCl4 loadings were all larger than 330 m2·g-1.Especially, the SiO2 nano-support with 0.17 g of the HAuCl4 loading was 550 m2·g-1.The reduction of p-nitrophenol(p-NPh) with sodium borohydride was used as the model reaction to evaluate the catalytic activity of Au/SiO2. The results indicate that determining factor of the catalytic activity of the Au/SiO2 NCPs is the particle size of Au NPs. Within the scope of this study, the catalytic activity of the Au/Si O2 NCPs decreased with the increase of the particle size of Au NPs. The reaction rate increased with the increase of the temperature from 20 °C to 40 °C, and the apparent activation energy in this temperature range was 31.2 kJ·mol-1. Further increase of the reaction temperature leaded to a slight decrease in the reaction rate.It has been shown that various types of noble metal/inorganic porous supports NCPs can be prepared through a combination of the sol–gel process in inverse miniemulsions and in situ reduction of the incorporated noble metal salts. The proposed technique in this thesis holds high versatility and flexibility to prepare supported noble metal NCPs with a complex morphology.