| As a major source for air pollution, nitrogen oxides (NOx) are harmful to human health and environment. Significant efforts have been made to effectively reduce NOx by the researchers. Considering the poor performance of commercial NH3-SCR catalysts, we prepared several zeolite-based catalysts on the basis of Al-rich Beta (synthesized without template) for improved low-temperature activity. Through the investigation of structure-activity relationship, the active species were revealed. Based on the abundant valence state of Mn species, we prepared several metal oxide-based low-temperature NH3-SCR catalysts. Through the study of intermediate, reaction mechanism was revealed. Moreover, we investigated the interaction of CuO with oxide supports for producing the7wt%CuO/10wt%CeO2/γ-Al2O3catalyst. The role of CuO clusters on the catalytic performance was revealed. The main results presented in the dissertation have been summarized as follows:1. Copper was introduced to the Al-rich Beta (Si/Al-4) by the ion-exchanged method for NH3-SCR. Compared with the Cu2+ions-exchanged conventional Beta catalysts (Cu-Beta-19), Cu-Beta-4showed better low-temperature catalytic performance. The characterization results indicated that more Cu2+ions exchange sites were obtained over Al-rich Beta, and the Cu2+ions which located in the exchange sites are the active sites for low-temperature SCR. In terms of the Fe3+ions-exchanged Beta, more tetrahedral isolated Fe3+species were obtained over Al-rich Beta, which are important to the low-temperature SCR activity.2. Compared to the Cu-based and Fe-based catalysts. Cu(3.0wt%)-Fe(1.3wt%)-Beta-4bi-component catalyst showed better low-temperature activity and wider temperature window. Due to Cu-Fe synergistic effect, the dispersion state of active components further improved compared to the mono-component catalysts. Cu2+and Fe3+which located in the exchange sites are the active sites in the low-temperature region, while FeOx clsters are more important in the high-temperature region. Moreover, sulfur resistance of the Cu(3.0wt%)-Fe(1.3wt%)-Beta-4sample significantly improved compared to Cu(4.1wt%)-Beta-4. During the high-temperature hydro thermal aging process, Fe(2.7wt%)-Beta-4showed the best aging resistence.3.20wt%MnOx/CeO2supported catalyst was prepared using the deposition-precipitation (DP) method for low-temperature NH3-SCR. A possible reaction pathway is proposed based on the results of an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study coupled with mass spectrometric (MS) data. It is suggested that SCR reaction on the20wt%MnOx/CeO2catalyst involves a [NH3…NO-] complex as an intermediate, the decomposition of which into N2and H2O is the rate-limiting step. The decomposition process would result in partly reduction of the catalyst surface, and the role of oxygen is to reoxidize the reduced surface, thereby completing the catalytic cycle.4. A strong interaction between a metal oxide and support has long been indicative of its promotion of catalytic activities. In connection with this, we investigated the interaction of CuO with γ-Al2O3and CeO2for producing highly efficient catalysts for CO, C3H6, and NO abatement. In particular, the dispersion and thermal aging resistance of CuO clusters on different supports were studied. CuO clusters can be stabilized by interaction with CeO2, while on γ-Al2O3they aggregated into larger particles at high CuO loadings. On the other hand, due to the poor thermal stability of CeO2, CuO clusters dispersed on it were sintered during an aging treatment at950℃. Accordingly, by pre-dispersing10wt%CeO2on γ-Al2O3followed by7wt%CuO dispersion, stabilized CuO clusters were obtained that were based on the superior aging resistance of the γ-Al2O3support. Therefore, better catalytic performance and thermal aging properties were obtained with a7wt%CuO/10wt%CeO2/γ-Al2O3catalyst as compared with7wt%CuO/γ-Al2O3and7wt%CuO/CeO2samples. |
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