Preparation Of High Surface Specific Area Silicon Carbide And Its Application In CO Oxidation Reaction

Silicon carbide (SiC) exihibits excellent mechanical strength, thermal stability and good thermal conductivity. Therefore, it has been widely used in the ceramic and abrasive industry. SiC is also regarded as a promising catalyst support material, and showed its superiority in many catalytic reactions. But the low specific surface area (in the range of 20—60m²/g) limit its application in the industry. So, it has important significant to synthesis high surface area silicon carbide. Tetraethoxysilane (TEOS) was used as silicon source and saccharose as carbon source for preparing the carbonaceous silicon xerogels via sol-gel method, the oxalic acid was used as catalyst for hydrolyzation of the TEOS, and the nickel was used as catalyst for carbothermal reaction. Then the xerogels were treated by the carbothermal reaction at high temperature under inert gas condition. XRD, IR, SEM, TEM and N₂ physisorption were carried out to characterize the obtain samples. A series of platinum catalysts was prepared, using silicon carbide with various of specific surface area as catalyst support. The CO oxidation activity of the catalysts was test under certain conditions. A kind of silicon carbide suit for CO oxidation was chose, and the effects of the promoters on the Pt/SiC catalyst activity was also investigated in this study. The results were showed as follows:1. The results of the preparing of silicon carbide precursor and carbothermal reaction under inert condition showed: the silicon carbide, prepared from the precursor without nickel at 1500℃, has a specific surface area of 157 m²/g, and it has a wide pore diameter distribution; the addition of the nickel catalyst shorten the gel time and decreased the carbothermal reaction temperature, and the addition of the nickel can result in the increasing of the size of the silicon carbide, but decreasing of the specific surface area.2. Changing the Ni addition to gain the silicon carbide with various surface specific area, and the silicon carbide was used as catalyst support for CO oxidation reaction, the result showed: the silicon carbide support prepared from the precursor with nickel was superior to the CO oxidation catalyst. The specific surface area of the silicon carbide also effect the catalyst activity, the larger the surface area of the silicon carbide, the higher the catalytic activity of the catalyst. The effects of Pt loading, calcination temperature were investigated in this study. When the Pt loading was 2wt %, the calcinations temperature was 500℃, the catalyst has the highest activity. Otherwise, the catalyst supported on the silicon carbide has relative high activity stability. 3. The tradition metals(Fe,Co,Ni) can promoter the catalytic activity, the co-impregnation method benefit the CO oxidation activity of the catalyst than stepwise impregnation methods. Fe promoter is superior to the catalytic activity. When the Fe loading was 2wt%, the catalyst exhibited the highest catalyst activity, further increasing the Fe loading resulted in the lower catalytic activity. The addition of the promoter can increase the Pt dispersion, and let to some interaction between Pt and Fe, thereby improving catalytic activity.4. The promote behavior of rare earth oxidation CeO₂ on the Pt/SiC was also investigated in this study, the result showed: CeO₂ can markedly improve the catalytic activity, and is superior to the tradition metals. When the CeO₂ loading is 8wt%, calcinations temperature was 500℃the catalyst got the highest activity. The addition of the CeO₂ increase the Pt dispersion on the silicon carbide support, and let to some interaction with Pt, so that improve the catalytic activity of the catalyst.