Untitled

The effect of Fe species distribution and acidity of Fe-ZSM-5 on the hydrothermal stability and SO2 and hydrocarbons durability in NH3-SCR reaction

“…The first peak in the H2-TPR profile of fresh Fe-NaZ can be also attributed to the reduction of Fe 3+ at exchanged sites to Fe 2+ . The main peaks at 484 °C and the small shoulder at 435 °C should correspond to reduction of larger FeOx particles [10,[12][13][14][15][16]. Fe species located at the same sites should show similar H2 reduction temperatures.…”

“…This suggests that the reduction of iron oxide particles completed below 650 °C, by the reduction of Fe2O3 to Fe3O4 and then reduction of FeOx to Fe 0 via FeO [10,[12][13][14][15][16]. According to previous work on the H2-TPR of Fe-ZSM-5 catalysts, the first reduction peak corresponds to the reduction of Fe 3+ to Fe 2+ [10,[12][13][14][15][16]. When Fe 3+ is located at ion-exchanged positions, further reduction of Fe 2+ to Fe 0 occurs at temperatures above 1000 °C owing to the collapse of the zeolite framework [10,12].…”

“…Protons remaining on zeolites are well known to accelerate the process of steam-induced aluminum loss [10,11,15]. Fe-NaZ contained fewer protonic sites than Fe-HZ, so the dealumination of the zeolite framework by hydrothermal deactivation occurred to a much lesser extent for Fe-NaZ.…”

Selective Catalytic Reduction of Nitric Oxide with Ammonia over ZSM-5 Based Catalysts for Diesel Engine Applications

“…After pretreatment of Fe/ZSM-5 in 10% H 2 O at 700°C for 24 h, the NO conversion decreased significantly in the low temperature range; however, at temperature higher than 400°C, the NO conversion was almost the same on the fresh and steampretreated Fe/ZSM-5. It is known that steam treatment at elevated temperatures will cause dealumination or aluminum migration in the ZSM-5 framework structure [24,25]. The dealumination of ZSM-5 results in an increase in the Si/Al ratio and a decrease in the surface acidity of the zeolite, thus the observed deactivation of Fe/ZSM-5.…”

“…The dealumination of ZSM-5 results in an increase in the Si/Al ratio and a decrease in the surface acidity of the zeolite, thus the observed deactivation of Fe/ZSM-5. In addition, the aging treatment also leads to the decrease of active iron species due to the formation of iron agglomerates and thus the deactivation of Fe/ZSM-5 [24][25][26]. It is considered that a high Si/Al ratio would increase the bond strength of NH 4 + on the zeolite whereas a low Si/Al ratio would increase the adsorption capacity [26].…”