Ratio of adsorptive abilities for NH3 and NOx determined SCR activity of transition-metal catalyst

Ce doped V-W/Ti as selective catalytic reduction catalysts for cement kiln flue gas denitration

In cement industry, the selection of catalyst temperature window and the inhibition effect of dust composition in flue gas on catalyst are the key issues of flue gas denitrification. In this article, a pilot study with Ce doped V-W/Ti catalyst on the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR) from the cement kiln flue gas was presented. Cement kiln dust loading on catalysts obviously decreased the NO conversion in the absence of SO2 and H2O, while the denitration efficiency restored from 75 to 98% at 280 ℃ after SO2 and H2O introduced into the reaction system, which mainly because the SO2 may enhance the acidic site on the catalyst surface, and prefer to be bonded with the coordinated Ca species, releasing the active sites poisoned by dust. The NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) detections were performed to reveal that the appropriate Ce and W ratios catalyst contributed better denitrification activity. The optimum ratio of Ce doped catalyst was amplified to form the standard honeycomb monomer catalyst, and then, the activity of catalyst was verified on the side line of cement kiln. The effect of temperature and space velocity on denitrification efficiency was investigated, and the denitration efficiency reached to 92.5% at 300℃ and 3000 h-1 space velocity. Moreover, the life of catalyst was verified and predicted by GM (1,1) grey model. The study realized the innovation from the laboratory data rules to the industrial pilot application, providing positive promoting value for the industrial large-scale demonstration application of the catalyst.

Denitrification activity test of a V modified Mn-based ceramic filter

In view of the characteristics of high temperature denitrification and low water and sulfur resistance of single manganese-based catalysts, a vanadium-manganese-based ceramic filter (VMA(14)-CCF) was prepared by the impregnation method modified with V. The results showed that the NO conversion of VMA(14)-CCF was more than 80% at 175-400 °C. At 225-300 °C, the conversion of NO can reach 100%. High NO conversion and low pressure drop can be maintained at all face velocities. The resistance of VMA(14)-CCF to water, sulfur and alkali metal poisoning is better than that of a single manganese-based ceramic filter. XRD, SEM, XPS and BET were further used for characterization analysis. The introduction of V protects the MnO_x center, promotes the conversion of Mn³⁺ to Mn⁴⁺, and provides abundant surface adsorbed oxygen. The development of VMA(14)-CCF greatly broadens the application range of ceramic filters in denitrification.

Recognizing zeolite topologies for Cu2+ localizations with effective activities for selective catalytic reduction of nitrogen oxide

Cu-loaded zeolites are widely investigated in selective catalytic reduction of nitrogen oxide, but effects of zeolite topologies on formed active species and the changing tendency remain unexplored. In this work, catalytic turnover frequencies (TOF) of Cu loaded ZSM-5, Beta, MOR, and SSZ-13 were first determined. The topology-localized Cu species in these zeolites were analyzed by temperature-programmed reduction of H₂. Then Multiple Linear Regression distinguished TOF contributions (k_j, s^-1·mol^-1) of the Cu species. Density functional theory calculated NH₃ dehydrogenation energy of the Cu species. As a result, topologies with more node atoms showed bigger k_j and lower dehydrogenation energies simultaneously. The best topology in each zeolite was 10-membered ring (ZSM-5), 6-membered ring facing a 12-membered ring (Beta), 8-membered ring (MOR), and cha cage (SSZ-13). Moreover, cha cage-localized Cu²⁺ exhibited the largest k_j and the lowest dehydrogenation energy among all the Cu species. This work reveals topology-catalysis relationships in the zeolite, which benefits zeolite design for enhanced catalytic performances.