VOx Surface Coverage Optimization of V2O5/WO3-TiO2 SCR Catalysts by Variation of the V Loading and by Aging

Abstract

V2O5/WO3-TiO2 selective catalytic reduction (SCR) catalysts with a V2O5 loading of 1.7, 2.0, 2.3, 2.6, 2.9, 3.2 and 3.5 wt. % were investigated in the fresh state and after hydrothermal aging at 600 °C for 16 h. The catalysts were characterized by means of nitrogen physisorption, X-ray diffraction and X-ray absorption spectroscopy. In the fresh state, the SCR activity increased with increasing V loading. Upon aging, the catalysts with up to 2.3 wt. % V2O5 exhibited higher NOx reduction activity than in the fresh state, while the catalysts with more than 2.6 wt. % V2O5 showed increasing deactivation tendencies. The observed activation and deactivation were correlated with the change of the VOx and WOx surface coverages. Only catalysts with a VOx coverage below 50% in the aged state did not show deactivation tendencies. With respect to tungsten, above one monolayer of WOx, WO3 particles were formed leading to loss of surface acidity, sintering, catalyst deactivation and early NH3 slip. An optimal compromise between activity and hydrothermal aging resistance could be obtained only with V2O5 between 2.0 and 2.6 wt. %.

Removal of NOX Using Hydrogen Peroxide Vapor over Fe/TiO2 Catalysts and an Absorption Technique

“…As shown in Figure 10, the observed hyperfine splitting constants for the 1:2:2:1 signal (aN = aH = 14.9 G) were the typical spectrum shape of the DMPO-OH spin adduct and were in good accordance with the values in the literature [44]. What is more, the concentration of •OH was in the order of: 2% Fe-TiO 2 Figure 10. EPR spectra of radical adducts with DMPO in H2O2, H2O2 + P25, H2O2 + TiO2, and H2O2 + 2% Fe/TiO2 systems.…”

“…The P25 and iron-doped titanium dioxides with different molar ratios (0, 0.5%, 1%, 2%, and 3%) showed similar spectral characteristics. The observed peaks at 144 cm −1 , 195 cm −1 , 395 cm −1 , 515 cm −1 , and 638 cm −1 belong to the Raman active of TiO2 with symmetries of Eg(1), Eg (2), B1g(1), B1g (2), and Eg(3), respectively [24,25]. It should be mentioned that no Fe-relevant structures could be observed in the sample obtained above 400 °C, confirming that the Fe atom may substitute for the Ti atom and be highly dispersed in the lattice of TiO2.…”

“…The post-combustion technologies, which mainly include the selective catalytic reduction method (SCR), the selective non-catalytic reduction method (SNCR), electron-beam, and absorption, are the primary methods for NO X elimination. As the most common way to control NO X , SCR is capable of achieving a high level of NO X removal efficiency: up to 85% [2]. Nevertheless, this process suffers from problems, such as a high and narrow operating temperature window (300-400 • C), NH 3 slip, and the poisoning of the catalyst [3].…”

Improving the Diagnosis Accuracy of Hydrothermal Aging Degree of V2O5/WO3–TiO2 Catalyst in SCR Control System Using an GS–PSO–SVM Algorithm

“…After a hydrothermal treatment, the results show that there is a significant loss of NO reduction activity for VWTi-con, while VWTi-HUST still has good hydrothermal stability. The work in Reference [17] [20] prepare the V 2 O 5 /WO 3 -TiO 2 catalyst by wetness impregnation method, and it is hydrothermally aged at 750 • C in 10 vol % H 2 O/air for 24 h. The result shows that the NO x removal ability of the V 2 O 5 /WO 3 -TiO 2 catalyst is severely and negatively affected by hydrothermal aging over the entire measured temperature range. From the above, the existing studies mainly focus on the experimental investigation of aging effects on SCR performance with different catalysts.…”

Automotive Emission Control Catalysts

“…The paper by Marberger et al [9] further clarifies the relationship between V loading and activity and selectivity, thus providing useful information for optimization of catalyst formulation and performance. An ideal V 2 O 5 loading is found between 2.0 and 2.6 wt.…”