The Research On The Preparations And NH₃-SCR Properties Of Ce-Ti-W-O_x Catalysts

NOx are regarded as the major atmospheric pollutants. The environmental issues have attracted extensive public attentions. The selective catalytic reduction (SCR) with NH3 is a state-of-the-art and well-proven technique for eliminating the NO*. Nowadays, V205-WO3(Mo03)/Ti02, as the commercial catalysts, have been characterised as exhibiting a high level of SCR activity and selectivity between 300 and 400 ℃. However, many drawbacks occur in the practical applications, such as a narrow temperature window, poor SCR activity at low temperature, formation of N2O at high temperature, and the bio-toxicity of vanadium. Therefore, investigating the recipes environmental-friendly catalysts and the technologies of the preparations has become an important topic of the researchers in this field.A number of transition metal oxides have been investigated. Among them, Cerium-based catalysts have been received much attentions for their impressive oxygen storage capacity. WO3 is introduced as catalysts promoter. Moreover, TiO2 can exhibit excellent sulfur tolerance and promotional effect to catalytic activity. Therefore, Ce-Ti-W-O, catalysts have been chosen to be investigated in NH3-SCR process.Based on the above background, new preparation methods have been developed or introduced and the NH3-SCR properties of Ce-Ti-W-Ox catalysts via new preparation methods have been investigated in current work.(1)A series of Ce-Ti-W-Ox catalysts were prepared by the hydrothermal method and applied to the NH3-SCR reaction. In activity test, the Ce-Ti-W-Ox catalysts via sol-gel method and impregnation method, were compared with the samples via the hydrothermal method. The experimental results showed that the Ce-Ti-W-Ox catalyst prepared by the hydrothermal method exhibited higher NO conversion (more than 90%) within a broad temperature window of 225-450 ℃ than those synthesised via the sol-gel and impregnating methods. Furthermore, the catalyst also exhibited good resistance to H2O and SO2. The samples were investigated by various characterization methods. It was found that the high efficiency of NO removal was due to the large BET surface area, the amorphous surface species, the change to element valence states, and the strong interaction between Ce, Ti, and W.(2) To investigate the possibility of using an aqueous-phase process to prepare the SCR (selective catalytic reduction) catalysts, an aqueous-phase process was introduced to fabricate the Ce-W-Ti-Ox catalysts. The experimental results showed that the Ce-W-Ti-Ox catalysts via the aqueous-phase process exhibited an excellent level of SCR activity within a broad temperature window of 225-500℃. Furthermore, the Ce-W-Ti-Ox catalysts via aqueous-phase process showed a good sulfur tolerance. The TiO2, which was introduced via the aqueous-phase process, tended to be distributed on the surface of the catalysts. In addition, the introduction of TiO2 enhanced the redox ability and the acidity of catalysts.