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The catalytic performances and mechanism differences of model catalysts Cu–SSZ-13 and Fe–SSZ-13 with similar metal content and Si/Al ratio were compared. In the NH3-SCR reaction, Cu–SSZ-13 had a good NO conversion at low temperature, broad active temperature windows and better hydrothermal stability. Fe–SSZ-13 showed better high-temperature NO conversion rate and better resistance to sulfur poisoning, but poorer low-temperature NH3-SCR activity. NH3-TPD verified the content difference of L-NH3 and B-NH3 of Cu- and Fe–SSZ-13. UV–Vis DRS, EPR, H2-TPR indicated the active species of Cu- and Fe–SSZ-13. Results showed that Cu–SSZ-13 only had one type active species of Cu2+, Fe–SSZ-13 had Fe3+ species that acted as active centers at low temperature and reactivity oligomeric Fe species at high temperature. The diffuse reflection infrared Fourier transform spectrum (DRIFTS) results showed that the reactions of Cu–SSZ-13 and Fe–SSZ-13 at low temperature both followed the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism. Cu–SSZ-13 could perform the catalytic process well under both mechanisms, but when Fe–SSZ-13 followed the E–R mechanism, there were many B-NH3 species, which was not conducive to the reaction. When following the L–H mechanism, the speed of NO3− participating in the reaction was slow due to ammonia inhibition, resulting in poor low-temperature activity. [ABSTRACT FROM AUTHOR]

Two types of apatite supports including hydroxyapatite (HAP) and fluorapatite (FAP) were prepared by the co-precipitation method. Supported Co catalysts with the above carriers were synthesized from Co(NO3)2·6H2O via the impregnation method. The catalytic activity for N2O decomposition was investigated using a continuous flowing microreactor system. The catalytic results demonstrated that the Co/HAP exhibited more excellent catalytic activity as well as the impurity gas (H2O, O2, and NO) resistance capability than the Co/FAP in the temperature range of 300–600 °C. Furthermore, the physicochemical properties of Co/HAP and Co/FAP were determined by several relevant characterization methods. The obtained experimental results revealed that Co/HAP possessed larger specific surface area, more ion-exchanged Co2+ and stronger oxygen desorption capacity than Co/FAP, which are the key factors for high N2O decomposition activity. Moreover, compared with Co/FAP, Co/HAP has not only more basic content, but also higher basic site density, which may be also conducive to enhance the electron donating ability of Co2+, thereby promoting the N2O catalytic decomposition. [ABSTRACT FROM AUTHOR]

In this paper, selective catalytic reduction (SCR) of N2O by CO was investigated over Fe-beta zeolites catalysts. The catalysts were prepared by wet ion-exchange (IE), impregnation (IM) and solid state ion-exchange (SSIE) methods. These catalysts were characterized by XRD, UV–vis DR spectroscopy, H2-TPR, TPD and in-situ DRIFTS. At 350 °C, more than 90% N2O conversion could be obtained over the Fe-beta-IE catalyst. The activity for N2O removal of Fe-beta-IE was higher than Fe-beta-IM and Fe-beta-SSIE catalysts. The UV–vis spectra showed that 84.2% of isolated Fe(III) ion appeared on Fe-beta-IE catalyst. It indicated that the isolated Fe(III) ions might be considered as the active sites for N2O reduction. Besides, in the presence of H2O, the activities in CO-SCR for N2O removal over Fe-beta catalysts were inhibited, which might be due to the hydroxylation deactivation of iron species and excess accumulation of carbonates. [ABSTRACT FROM AUTHOR]

The Cu/SAPO-18 samples with different Cu/Al mass ratios were prepared, their catalytic activities for the NH3-SCR of NO in simulated diesel exhaust were evaluated, and effects of Cu/Al mass ratio and hydrothermal aging temperature on catalytic performance of Cu/SAPO-18 was examined. Physicochemical properties of the samples were characterized by means of various techniques. It is found that the activity of the sample changed with a rise in Cu/Al mass ratio, with the highest overall activity being achieved over the sample with a Cu/Al mass ratio of 0.045. The H2-TPR results indicate that the Cu/Al mass ratio could affect the distribution of Cu species, and the Cu/SAPO-18-0.045 sample possessed the highest amount of the isolated Cu2+ species. BET and XRD results reveal that the Cu/Al mass ratio exerted little effect on the structure of the sample. Low-temperature hydrothermal treatment had the least influence on the sample, and the effect of high-temperature hydrothermal treatment on the sample became increasingly obvious with a rise in hydrothermal treatment temperature. It is concluded that the hydrothermal aging treatment mainly affected the sample by destroying the structure, blocking the pores, migration and transformation of the Cu species, and changing the acidic sites of the sample. [ABSTRACT FROM AUTHOR]

Catalytic elimination is an important technique to reduce the emission of atmospheric molecular contaminants (such as NOx) efficiently. Selective catalytic reduction (SCR) is one of the most important nitrogen oxide (NOx) control technologies in the world, and catalyst plays a greatly important role in SCR process. In this field, the novel catalysts and preparation methods have attracted more and more attention in recent years due to their excellent catalytic performance. It is well accepted that catalytic performance is significantly dependent on the supports, active sites, and interaction of support and active component of the catalysts. In this paper, we present a brief review on the preparation methods of different kinds of SCR catalysts in recent years and propose some perspectives for further development. Based on the report of published literatures, the structure-activity relationship between support and active sites is deeply analyzed. Meanwhile, we review the possible catalytic mechanism, and further clarify the nature of the catalytic reactions. [ABSTRACT FROM AUTHOR]