A critical review towards the causes of the iron-based catalysts deactivation mechanisms in the selective oxidation of hydrogen sulfide to elemental sulfur from biogas

Hydrogen sulfide(H_(2)S) not only presents significant environmental concerns but also induces severe corrosion in industrial equipment,even at low concentrations.Among various technologies,the selective oxidation of hydrogen sulfide(SOH_(2)S) to elemental sulfur(S) has emerged as a sustainable and environmentally friendly solution.Due to its unique properties,iron oxide has been extensively investigated as a catalyst for SOH_(2)S;however,rapid deactivation has remained a significant drawback.The causes of iron oxide-based catalysts deactivation mechanisms in SOH_(2)S,including sulfur or sulfate deposition,the transformation of iron species,sintering and excessive oxygen vacancy formation,and active site loss,are thoroughly examined in this review.By focusing on the deactivation mechanisms,this review aims to provide valuable insights into enhancing the stability and efficiency of iron-based catalysts for SOH_(2)S.

Effect of liming on sulfate transformation and sulfur gas emissions in degraded vegetable soil treated by reductive soil disinfestation

Reductive soil disinfestation（RSD）, namely amending organic materials and mulching or flooding to create strong reductive status, has been widely applied to improve degraded soils.However, there is little information available about sulfate（SO4^2-） transformation and sulfur（S）gas emissions during RSD treatment to degraded vegetable soils, in which S is generally accumulated. To investigate the effects of liming on SO4^2-transformation and S gas emissions,two SO4^2--accumulated vegetable soils（denoted as S1 and S2） were treated by RSD, and RSD plus lime, denoted as RSD0 and RSD1, respectively. The results showed that RSD0 treatment reduced soil SO4^2-by 51% and 61% in S1 and S2, respectively. The disappeared SO4^2-was mainly transformed into the undissolved form. During RSD treatment, hydrogen sulfide（H2S）,carbonyl sulfide（COS）, and dimethyl sulfide（DMS） were detected, but the total S gas emission accounted for 〈 0.006% of total S in both soils. Compared to RSD0, lime addition stimulated the conversion of SO42-into undissolved form, reduced soil SO4^2-by 81% in S1 and 84% in S2 and reduced total S gas emissions by 32% in S1 and 57% in S2, respectively. In addition to H2S, COS and DMS, the emissions of carbon disulfide, methyl mercaptan, and dimethyl disulfide were also detected in RSD1 treatment. The results indicated that RSD was an effective method to remove SO4^2-, liming stimulates the conversion of dissolved SO4^2-into undissolved form,probably due to the precipitation with calcium.

Effect of barium sulfate modification on the SO2 tolerance of V2O5/TiO2 catalyst for NH3-SCR reaction

Sulfur poisoning of V_2O_5/BaSO_4–TiO_2（VBT）,V_2O_5/WO_3–TiO_2（VWT） and V_2O_5/BaSO_4–WO_3–TiO_2（VBWT） catalysts was performed in wet air at 350℃ for 3 hr,and activities for the selective catalytic reduction of NO_x with NH_3 were evaluated for 200–500℃.The VBT catalyst showed higher NO_x conversions after sulfur poisoning than the other two catalysts.The introduction of barium sulfate contributed to strong acid sites for the as-received catalyst,and eliminated the redox cycle of active vanadium oxide to some extent,which resulted in a certain loss of activity.Readily decomposable sulfate species formed on VBT-S instead of inactive sulfates on VWT-S.These decomposable sulfates increased the number of strong acid sites significantly.Some sulfate species escaped during catalyst preparation and barium sulfate was reproduced during sulfur poisoning,which protects vanadia from sulfur oxide attachment to a great extent.Consequently,the VBT catalyst exhibited the best resistance to sulfur poisoning.

Effects of SO2 on the low temperature selective catalytic reduction of NO by NH3 over CeO2-V2O5-WO3/TiO2 catalysts

The CeO2-V2O5-WO3/TiO2 （CeO2-VWT） catalysts were prepared by one-step and two-step impregnation methods. The effects of different loading of CeO2 and different preparation methods on De-NOx activity of catalysts had been investigated. CeO2 helped to improve the De-NOx activity and sulfur resistance. The optimal loading of CeO2 was 3% with the De-NOx efficiency reached 89.9% at 140℃. The results showed that the De-NOx activity of 3% CeO2-VWT catalysts by one-step method was the same as two-step method basically and reached the level of industrial applications, the N2 selectivity of catalysts was more than 99.2% between 110℃ and 320℃. In addition, CeO2 promoted the oxidation of NO to NO2, which adsorbed on the Lewis acid site （V5＋-O） to form V5＋-NO3 and inspired the fast SCR reaction. Not only the thermal stability but also the De-NOx activity of catalysts decreased with excess CeO2 competed with V2O5. Characterizations of catalysts were carried out by XRF, BET, XRD, TG and FT-IR. BET showed that the specific surface area of catalysts decreased with the loading of CeO2 increased, the active components content and specific surface area of catalysts decreased slightly after entering SO2. Ammonium sulfate species were formed in poisoned catalyst which had been investigated by XRF, BET, TG and FT-IR. The largest loss rate of weight fraction was 0.024%.℃-1 at 380℃ 390℃, which was in accordance with the decomposition temperature of NH4HSO4 and （NH4）2SO4,