Catalytic Oxidation of 1,2-Dichlorobenzene over Silica Supported Vanadia Catalysts：Role of TiO2, WO3, MoO3 Promoter

• Main Authors: Huang, Yuting, 黃鈺婷
• Other Authors: Chang, Jenray
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/37577610175799166764

碩士 === 國立中正大學 === 化學工程研究所 === 101 === The goals of this study was to investigate the roles of V2O5-TiO2 interactions in improving vanadia catalysts for oxidative destruction of 1, 2-dichlorobenzene and to examine the feasibility of improving catalytic properties by the addition of MoO3 and WO3 in vanadia catalyst. V2O5/TiO2 (VT) and V2O5/TiO2-SiO2 (VTQ) catalysts were prepared by impregnation technique. Vanadium oxalate were incorporated into anatase TiO2 nano-particles and TiO2-SiO2 supports, respectively, and then followed by calcination at temperature ranging from 350 to 700 C. The prepared catalyst samples were characterized by synchrotron powder X-ray diffraction (PXRD), Extend X-ray adsorption fine structure (EXAFS), X-ray adsorption near edges structure (XANES), and Fourier-transformed infrared spectroscopy (FT-IR). Accelerated-aging tests were performed to evaluate the catalytic performance and were carried out in a continued fixed bed under 1 atm in air with temperature elevated from 200oC to 550oC. The activity loss in the test was estimated from the difference of conversion for the fresh and aged catalyst run at 350oC. TiVO4 formed on TiO2, evidenced by PXRD, suggested the existence of V2O5-TiO2 interactions. FT-IR further indicated that vanadia-titania interactions were increased with the elevation of calcination temperature. Compared with V2O5/SiO2 (VQ) catalyst, VT catalysts present lower vanadia dispersion but higher o-DCB conversion, suggesting that vanadia activity is enhanced by the interactions. However, VT catalysts suffered from low surface area, low thermal stability, and high cost of TiO2 nano-particles support. To remedy the drawbacks of of TiO2 while keep the merits of V2O5-TiO2 interactions, TiO2-SiO2 supports were prepared by grafting TiO2 on SiO2 supports. As expected, the experimental data indicated that the catalytic properties of the vanadia catalysts was greatly improved by the use of TiO2-SiO2 supports. Based on FT-IR, EXAFS, and XANES results, we proposed that the improvement of the catalytic properties by V2O5-TiO2 interactions are mainly resulted from the reduce of oxygen-containing intermediate strongly adsorbed on the active sites due to the decrease of coordination charge of vanadium and the increase of the active sites due to the disruption of V-O-Ti bonds in the test reaction. It has been reported that VT catalyst can be promoted by MoO3 and WO3. Inferred from this results, we expected that V2O5/TiO2-SiO2 (VTQ) can further be improved by the addition of these metal oxides. Unfortunately, at this moment, opposites were observed in the performance tests.