ABSTRACT
In this study, a core-shell catalyst of Cu-SAPO-34@Fe-MOR was successfully prepared through a silica-sol adhesion method, and its performance for selective catalytic reduction of nitric oxide by NH3 (NH3-SCR) was evaluated in detail. The Fe-MOR coating has not only increased the high-temperature activity and broadened the reaction temperature window of Cu-SAPO-34 to a large extent, but also increased the hydrothermal stability of Cu-SAPO-34 markedly. It is demonstrated that a strong synergistic interaction effect exists between Cu2+ and Fe3+ ions and promotes the redox cycle and oxidation-reduction ability of copper ions, which greatly accelerates the catalytic performance of the core-shell Cu-SAPO-34@Fe-MOR catalyst. Abundant isolated Cu2+ ions and Fe3+ ions on the ion exchange sites performing NO x reduction at low and high temperature region lead to the broad reaction temperature window of Cu-SAPO-34@Fe-MOR. In addition, more weakly adsorbed NO x species formed and the increased number of Lewis acid sites may also contribute to the higher catalytic performance of Cu-SAPO-34@Fe-MOR. On the other hand, the better hydrothermal ageing stability of Cu-SAPO-34@Fe-MOR is related to its lighter structural collapse, fewer acidic sites lost, more active components (Cu2+ and Fe3+) maintained, and more monodentate nitrate species formed in the core-shell catalyst after hydrothermal ageing. Last, the mechanism study has found that both Langmuir-Hinshelwood ("L-H") and Eley-Rideal ("E-R") mechanisms play an essential role in the catalytic process of Cu-SAPO-34@Fe-MOR, and constitute another reason for its higher activity compared with that of Cu-SAPO-34 (only "L-H" mechanism).
ABSTRACT
OBJECTIVE@#To explore MSCT optimal examination time for patients with unconspicuous rib fracture.@*METHODS@#Sixty-three patients with thoracic trauma from January 2009 to June 2011 were collected. They were examined by MSCT in the first week after trauma and re-examined during eighth weeks after trauma. The number of rib which had been found fractured in the first examination was compared to that in re-examinations.@*RESULTS@#Patients with fine rib fracture often have different diagnostic results at different examination time after trauma. There was statistical difference between the number in the first week and the third week to the fifth week.@*CONCLUSION@#MSCT could show the pathophysiological changes of rib fracture objectively in the stage between the third week and the fifth week after trauma, which is optimal examination time for the fine rib fracture.
