| Due to the high calorific value, high efficiency, low pollutant emission and economical energy price, natural gas has increasingly becoming the main source of a new generation of energy. While, the traditional use of methane usually have low utilization of heat and often accompanied by environmental pollution. Catalytic oxidation is considered to be the most promising and environmental-friendly pathway for the clean combustion of methane. Usually, catalytic performance is often affected by micro-structure of the catalyst, and the catalyst is generally very difficult to synthesize long-range order micro-structure. In recent years, more and more people cast attention to the mesoporous silica material because of its highly ordered pore structure, large specific surface area, controllable pore wall thickness and good thermal stability. Adopting those ordered mesoporous silica material as hard template provides a new method for the synthesis of long-range order microporous catalysts. Among those mesoporous silica material (MCM-41, SBA-15, SBA-16, KIT-6 etc.), SBA-15 (two-dimensional) and KIT-6 (three-dimensional) was more preferable. Catalysts prepared by SBA-15 and KIT-6 as templates exhibited well in the catalytic combustion of volatile organic compounds. While, the application in the catalytic combustion of methane was still less. Preparation of 2D-Co3O4 and 3D-Co3O4 catalytic adopting SBA-15 and KIT-6 as templates and probing their methane catalytic activation was carried out as following:In the synthesis of SBA-15 and KIT-6, we adopting the three-block copolymer P123 as an organic template and tetraethylorthosilicate as the silicon source. Experimental results show that the obtained SBA-15 and KIT-6 are both highly ordered mesoporous silica materials. Wherein the two-dimensional SBA-15 having a highly ordered hexagonal pore structure. The channel pore size is about 6-8nm and the particle showing the micro structure of a section of the rod-like rules with a size of 0.6um. While KIT-6 possessing a inter biconnected pore structure. The channel pore size is about 5-6nm and the particle showing irregular block structure.2D-Co3O4 and 3D-Co3O4 was prepared adoption SBA-15 and KIT-6 as templates and cobalt nitrate as precursor and nano-Co3O4 was prepared by calcination of cobalt nitrate as a comparison. All the catalysts were tested for the total oxidation of methane in the temperature rage of 200-500℃ and their catalytic performance was in order of 3D-Co3O4> 2D-Co3O4> nano-Co3O4.90% methane conversion over 3D-Co3O4,2D-Co3O4 and nano-Co3O4 were achieved at 355,383 and 453℃, respectively. The methane catalytic activity that normalized by BET surface areas was also follow the same order with overall catalytic activity. Characterization results showed that the excellent catalytic performance of mesoporous catalysts in methane oxidation can be attributed to active surface oxygen species and abundant active Co3+ cationic species exposed on the main exposed{220} active crystal planes and the highly ordered open mesoporous architecture inherited from the silica hard templates. The conversion of methane had remained the same after those Co3O4 catalysts was observed for 12h at 300℃. Therefore, the mesoporous Co3O4 catalysts especial for 3D-Co3O4 catalyst have the best catalysts activity toward methane combustion.Spinel 3D-CoCr2O4 catalyst was prepared adopting KIT-6 as template and nano-CoCr2O4 catalyst was obtained by calcination method. All the catalysts were tested for the total oxidation of CH2Cl2. Experimental results show that the obtained 3D-CoCr2O4 catalyst also has ordered mesoporous structure. In the catalytic activity of CH2Cl2, the catalytic activity of 3D-CoCr2O4 catalyst was significantly higher than the 3D-Co3O4 catalyst, indicating that the three-dimensional mesoporous structure has a significant role in promoting the catalytic activity and the Chromium based catalysts have obvious advantages on the oxidation activity of chlorinated organic compounds CH2Cl2. |
PDF Full Text Request