Presence Of SO2 Research Articles

Catalytic performance of Cu/Hβ catalysts for selective catalytic reduction of NO with NH3

A series of Cu(x)/Hβ catalysts were prepared by the impregnation method and the effect on the performance of the catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR) was investigated. Characterization techniques such as XRD, N2 adsorption-desorption, NH3-TPD, NO-TPD, H2-TPR, EDS and XPS were used to investigate the physical and chemical properties of the catalysts and the reason of the decrease of catalyst activity in the presence of SO2. It was shown that the catalyst Cu(3)/Hβ, the Cu loading was 3% and Cu(2)/Hβ, the Cu loading was 2%, exhibited the better catalytic activity when the initial reaction material contained no SO2 and SO2, and t95 was 169 and 225 °C, respectively. The analysis results of the catalyst before and after the reaction showed that the main reason for the decrease of catalyst activity in the presence of SO2 was that the ammonium sulfur salt which was formed by the reaction of SO2 and NH3 in the low reaction temperature covers the catalyst active center.

Sensory Specificities Involving Acetaldehyde and Diacetyl in Wines Produced without Added Sulfur Dioxide.

Nowadays, the development of naturality concept is illustrated in the oenological field by the development of wine produced without the addition of SO2. Among its chemical properties, SO2 is able to react with carbonyl compounds to form carbonyl bisulfites. Acetaldehyde and diacetyl are the main carbonyl compounds of red wines, which could influence product perception. The goal of this paper was to evaluate their chemical and sensory impact in red wines produced without any addition of SO2. A first quantification approach revealed a lower concentration of these compounds in wines without added SO2 than in those produced with SO2. A sensory approach involving aromatic reconstitutions in wines in the presence or absence of SO2 revealed that analytical differences observed for acetaldehyde and diacetyl were able to impact wine freshness, with diacetyl being, moreover, involved in wine fruity aroma changes.

Effects of SO2 on NH4NO3 Photolysis: The Role of Reducibility and Acidic Products.

Nitrate photolysis is a vital process in secondary NOx release into the atmosphere. The heterogeneous oxidation of SO2 due to nitrate photolysis has been widely reported, while the influence of SO2 on nitrate photolysis has rarely been investigated. In this study, the photolysis of nitrate on different substrates was investigated in the absence and presence of SO2. In the photolysis of NH4NO3 on the membrane without mineral oxides, NO, NO2, HONO, and NH3 decreased by 17.1, 6.0, 12.6, and 57.1% due to the presence of SO2, respectively. In the photolysis of NH4NO3 on the surface of mineral oxides, SO2 also exhibited an inhibitory effect on the production of NOx, HONO, and NH3 due to its reducibility and acidic products, while the increase in surface acidity due to the accumulation of abundant sulfate on TiO2 and MgO promoted the release of HONO. On the photoactive oxide TiO2, HSO3-, generated by the uptake of SO2, could compete for holes with nitrate to block nitrate photolysis. This study highlights the interaction between the heterogeneous oxidation of SO2 and nitrate photolysis and provides a new perspective on how SO2 affects the photolysis of nitrate absorbed on the photoactive oxides.

Insight into the temperature-dependent SO2 resistance over Mn-based de-NOx catalyst

Herein, two simple model catalysts (Mn3O4 and MnFeOx) were fabricated and operated under different temperatures (100, 150, 200, 250 °C) in SCR atmosphere with the presence of SO2, followed by thermal regeneration and characterizations to reveal the deactivation mechanism and the role of FeOx. The results indicated both catalysts exhibited temperature-dependent deactivation behavior, where the total activity loss displayed volcano-type SO2 resistance tendency within 100–250 °C and the most severe activity loss (98 % for Mn3O4 and 81 % for MnFeOx) was found at 150 °C. Meanwhile, the higher relative proportion of irreversible activity loss was found at lower temperatures, which is associated with the more easily saturated chemical adsorption of SO2 as evidenced by SO2+O2 breakthrough test. At higher temperatures, the SO2 oxidation and its further transformation into NH4HSO4 could be favored, thus resulting in increased reversible activity loss. The FeOx modification can protect MnOx species from sulfation to a certain degree and lower the irreversible deactivation, which is evidenced by the binding energy upshift and downshift of Fen+ species after being poisoned and regenerated, as well as the slightly changed binding energy of Mnn+ species from the XPS analysis.

Oxidation of Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances by Sulfate and Hydroxyl Radicals: Kinetic Insights from Experiments and Models.

Per- and polyfluoroalkyl substances (PFAS) are widely used anthropogenic chemicals. Because of the strength of the carbon-fluorine bond, PFAS are not destroyed in typical water treatment processes. Sulfate (SO4•-) and hydroxyl (•OH) radicals can oxidize some PFAS, but the behavior of per- and polyfluoroalkyl ether acids (PFEAs) in processes involving SO4•- and •OH is poorly understood. In this study, we determined second-order rate constants (k) describing the oxidation of 18 PFAS, including 15 novel PFEAs, by SO4•- and •OH. Among the studied PFAS, 6:2 fluorotelomer sulfonate reacted most readily with •OH [k•OH = (1.1-1.2) × 107 M-1 s-1], while polyfluoroalkyl ether acids containing an -O-CFH- moiety reacted more slowly [k•OH = (0.5-1.0) × 106 M-1 s-1]. In the presence of SO4•-, polyfluoroalkyl ether acids with an -O-CFH- moiety reacted more rapidly [kSO4•- = (0.89-4.6) × 106 M-1 s-1] than perfluoroalkyl ether carboxylic acids (PFECAs) and a chloro-perfluoro-polyether carboxylic acid (ClPFPECA) [kSO4•- = (0.85-9.5) × 104 M-1 s-1]. For homologous series of perfluoroalkyl carboxylic acids, linear and branched monoether PFECAs, and multiether PFECAs, PFAS chain length had little impact on second-order rate constants. SO4•- reacted with the carboxylic acid headgroup of perfluoroalkyl carboxylic acids and PFECAs. In contrast, for polyfluoroalkyl ether carboxylic and sulfonic acids with an -O-CFH- moiety, the site of SO4•- attack was the -O-CFH- moiety. Perfluoroalkyl ether sulfonic acids were not oxidized by SO4•- and •OH under the conditions evaluated in this study.

The Enhancement of CO Oxidation Performance and Stability in SO2 and H2S Environment on Pd-Au/FeOX/Al2O3 Catalysts.

Carbon monoxide (CO) is a colourless, odourless, and toxic gas. Long-term exposure to high concentrations of CO causes poisoning and even death; therefore, CO removal is particularly important. Current research has focused on the efficient and rapid removal of CO via low-temperature (ambient) catalytic oxidation. Gold nanoparticles are widely used catalysts for the high-efficiency removal of high concentrations of CO at ambient temperature. However, easy poisoning and inactivation due to the presence of SO2 and H2S affect its activity and practical application. In this study, a bimetallic catalyst, Pd-Au/FeOx/Al2O3, with a Au:Pd ratio of 2:1 (wt%) was formed by adding Pd nanoparticles to a highly active Au/FeOx/Al2O3 catalyst. Its analysis and characterisation proved that it has improved catalytic activity for CO oxidation and excellent stability. A total conversion of 2500 ppm of CO at -30 °C was achieved. Furthermore, at ambient temperature and a volume space velocity of 13,000 h-1, 20,000 ppm CO was fully converted and maintained for 132 min. Density functional theory (DFT) calculations and in situ FTIR analysis revealed that Pd-Au/FeOx/Al2O3 exhibited stronger resistance to SO2 and H2S adsorption than the Au/FeOx/Al2O3 catalyst. This study provides a reference for the practical application of a CO catalyst with high performance and high environmental stability.

SO2-tolerant mesoporous iron oxide supported bimetallic single atom catalyst for methanol removal

Among the single-atom catalysts (SACs), the bimetallic single-atom catalysts play an increasingly promising role in the oxidative removal of volatile organic compounds (VOCs) due to their high efficiency. However, it remains a significant challenge to resist SO2 poisoning in industrial applications. In this work, we report (i) the synthesis of three-dimensionally ordered mesoporous Fe2O3-supported bimetallic AuPt single-atom (denote as Au1Pt1/meso-Fe2O3) catalyst via a modified polyvinyl alcohol-protected reduction route; (ii) catalytic performance of the catalysts for methanol oxidation; and (iii) catalytic and SO2-resistant mechanism. It was found that compared with Pt1/meso-Fe2O3 and Ptnp/meso-Fe2O3, Au1Pt1/meso-Fe2O3 exhibited better catalytic activity for methanol combustion, with the temperature at 90% methanol conversion, TOFnoble metal at 120 °C, and apparent activation energy being 137 °C at a space velocity of 20 000 mL g–1 h–1, 6.51 × 10–2 s–1, and 36 kJ mol− 1, respectively. The enhanced activity was associated with the improved reducibility, methanol adsorption ability, and strong interaction between noble metal and support. The reaction pathway was deduced to follow a sequence of methanol → methoxy species → formaldehyde → formic acid → CO2 and H2O. Furthermore, the order of SO2 resistance was Au1Pt1/meso-Fe2O3 > Pt1/meso-Fe2O3 > Ptnp/meso-Fe2O3. The good SO2 resistance of the Au1Pt1/meso-Fe2O3 catalyst was attributed to the Au−Pt bimetallic single atoms uniformly dispersed on the meso-Fe2O3 with the strong ability of sulfate decomposition and the protection of the active sites by meso-Fe2O3 as a sacrificial site. This work presents a novel way for developing high-performance catalysts for VOCs elimination in the presence of SO2.

Enhanced Stability of Low-Temperature CO Oxidation over K2CO3 Coupled CuO–MnOx–CeO2 Catalyst in the Presence of CO2, SO2 and NO2

Enhanced Stability of Low-Temperature CO Oxidation over K2CO3 Coupled CuO–MnOx–CeO2 Catalyst in the Presence of CO2, SO2 and NO2

Mechanistic and performance insights into low-temperature NH3-SCR based on Ce-modified Mn-Ti catalysts

In this study, Mn-Ti supported Ce catalysts (derived from manganese tailings) were synthesized by coprecipitation method. The denitration performance and SO2 resistance of the catalysts were investigated. The results showed that introducing Ce oxides into Mn-Ti catalyst improved the low temperature catalytic performance, with almost 100% NO conversion at 225 °C. Additionally, the N2 selectivity was improved due to the decrease in lattice oxygen. The modified catalyst also presented excellent SO2 resistance, with around 80% NO conversion after 10 h of SO2 injection. The modified catalyst had higher ratios of Mn4+ and Mn3+ species, stronger surface acidity, and more redox properties than the Mn-Ti catalyst, which improved NH3-SCR performance. After SO2 poisoning, the surface Lewis acidity decreased and the surface Brønsted acidity became stronger, indicating that the loss of Lewis acidity might cause the decrease of NO conversion. Moreover, the nitrate species on Mn-Ti catalyst were less than those on Mn-Ce-Ti catalyst in the presence of SO2, suggesting that doping Ce into Mn-Ti catalyst retained more oxidation performance after being poisoned by SO2.

Multiple doping of cryptomelane catalysts by Co, Cu, Ag and Ca for efficient soot oxidation and its effect on NO2 formation and SO2 resistance

Two series of cryptomelane doped with Cu2+ and Ag+ ions were synthesized by coprecipitation method, and additionally impregnated with Ca2+, Co2+ and Ag+ ions to obtain bi- and tri-metallic catalysts. The samples were thoroughly characterized by XRD, RS, TEM/EDX, XRF and XPS. The catalysts were tested for soot oxidation in the loose contact mode in various reaction conditions (O2, O2 + NO, O2 + SO2, and O2 + NO + SO2). The role of doping was examined and discussed in terms of its influence on catalytic soot oxidation performance, NO2 formation in the course of the combustion, and resistance to SO2. It was found that NO2 production in the course of soot oxidation is strongly enhanced upon doping, and clearly depends on the dopants nature. However, it does not directly correlate with the catalysts activity, which in the O2/NO mixture is rather weakly sensitive to the type of doping. This observation was interpreted in terms of a critical amount of NO2, which actually can be utilized effectively for soot combustion. The excess of NO2 gains in importance in the presence of SO2, accounting for the beneficial role of doping in improving the resistance to sulphur poisoning of the cryptomelane catalyst.

Influence of bicarbonate, other anions and carbon dioxide in the activity of Pd-Cu catalysts for nitrate reduction in drinking water

Synthetic and commercial drinking waters with different composition were studied as reaction media to study the influence of salts in NO3- catalytic reduction using a Pd-Cu catalyst supported on a carbon black. As a general trend, a decrease in NO3- conversion and an increase in NH4+ selectivity were observed for high HCO3- concentration media in mixed salts waters. Literature has commonly ascribed HCO3- effect to competitive adsorption with NO3-. However, in the current work, the mechanism for effect HCO3- is reconsidered basis on HCO2- formation during NO3- catalytic reduction, here reported for the first time. HCO2- formation indicates that hydrogenation of HCO3- occurs in addition to adsorption. Likewise, decomposition of HCO2- on the catalysts surface releases hydrogen leading to increased spill-over and relevant hydrogenation of NO3- to NH4+. The presence of SO42-, Cl- reduces NH4+ selectivity due to competition for active sites and lower HCO2- generation. Furthermore, it was observed that the use of CO2 as buffer also contribute to the hydrogenation of NO3- to NH4+ through HCO2- route.

Synergistic oxidation of NH3 and Hg0 over Cu-ATP catalyst: Influence of SO2 and reaction mechanisms

NH3 and Hg0 could be synergistically oxidized by copper modified attapulgite (Cu3-ATP) catalyst at the gas hourly space velocity (GHSV) below 5 × 104 h−1 despite competition exist between these two reactions. Its Hg0 oxidation showed good sulfur resistance when HCl was present, but the NH3 oxidation was partially inhibited after SO2 was added. In order to explain this phenomenon, the composition and physical characteristics of Cu3-ATP before and after sulfurization were characterized by XRF, BET, XRD and FTIR. And H2-TPR, NH3-TPD, in situ DRIFT and XPS of the catalysts were adopted to reveal the influence of SO2 on NH3/Hg0 oxidation and the reaction mechanisms. The results showed that SO2 would adsorb and oxidize on the catalyst surface to form very small amount of sulfite and sulfate species, and partially change the composition and structure of Cu3-ATP. This reduced the reducibility of Cu3-ATP and increased the weak and moderate acid sites on its surface. The presence of SO2 was beneficial to NH3 adsorption, but inhibited NH2 → NOx conversion in iSCR mechanism for NH3 oxidation. Cl2 formation were also inhibited by SO2, while the generated surface active Cl and O species could ensure high Hg0 oxidation efficiency.

Insight into the enhanced tolerance of Mo-doped CeO2-Nb2O5/TiO2 catalyst towards the combined effect of K2O, H2O and SO2 in NH3-SCR

MoO3-doped CeO2-Nb2O5/TiO2 catalyst was synthesized by a sol–gel method. It was found that Mo doping observably enhanced the tolerance of CeO2-Nb2O5/TiO2 catalyst to the combined poisoning of H2O, SO2 and K2O. Mo doping could restrain the generation of ammonium sulfate and metal sulfate on the surface of the catalyst. This came down to the large specific surface area, strong acidity and superior redox performance of CeO2-MoO3-Nb2O5/TiO2 catalyst. In situ DRIFTS results indicated that K/S/H-CMNT catalyst still proceeded the SCR reaction according to the L-H and E-R mechanisms together, while K/S/H-CNT catalyst only followed the E-R mechanism. Mo doping could enhance the adsorption of NH3 and NOx species in the presence of K2O, H2O, and SO2.

Mechanism of nitro-byproducts formation during persulfate-based electrokinetic in situ oxidation for remediation of anthracene contaminated soil

Persulfate-based electrokinetic (EK) chemical oxidation appears to be a novel and viable strategy for the in situ remediation of polycyclic aromatic hydrocarbons (PAHs) polluted soil; however, the possible toxic byproducts of PAHs have been overlooked. In this study, we systematically investigated the formation mechanism of the nitro-byproducts of anthracene (ANT) during the EK process. Electrochemical experiments revealed that NH4+ and NO2- originating from nitrate electrolyte or soil substrates were oxidized to NO2• and NO• in the presence of SO4•-. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS/MS) analysis with 15N labeling revealed the formation of nitro-byproducts (14 kinds), including 1-hydroxy-4-nitro-anthraquinone and its similar derivatives, 4-nitrophenol, and 2,4-dinitrophenol. The nitration pathways of ANT have been proposed and described, mainly including the formation of hydroxyl-anthraquinone-oxygen and phenoxy radicals and the subsequent addition of NO2• and NO•. ANT-based formation of nitro-byproducts during EK, which is usually underestimated, should be further investigated due to their enhanced acute toxicity, mutagenic effects, and potential threat to the ecosystem.

PdPtVOx/CeO2−ZrO2: Highly efficient catalysts with good sulfur dioxide-poisoning reversibility for the oxidative removal of ethylbenzene

The PdPtVOx/CeO2−ZrO2 (PdPtVOx/CZO) catalysts were obtained by using different approaches, and their physical and chemical properties were determined by various techniques. Catalytic activities of these materials in the presence of H2O or SO2 were evaluated for the oxidation of ethylbenzene (EB). The PdPtVOx/CZO sample exhibited high catalytic activity, good hydrothermal stability, and reversible sulfur dioxide-poisoning performance, over which the specific reaction rate at 160°C, turnover frequency at 160°C (TOFPd or Pt), and apparent activation energy were 72.6 mmol/(gPt⋅sec) or 124.2 mmol/(gPd⋅sec), 14.2 sec−1 (TOFPt) or 13.1 sec−1 (TOFPd), and 58 kJ/mol, respectively. The large EB adsorption capacity, good reducibility, and strong acidity contributed to the good catalytic performance of PdPtVOx/CZO. Catalytic activity of PdPtVOx/CZO decreased when 50 ppm SO2 or (1.0 vol.% H2O + 50 ppm SO2) was added to the feedstock, but was gradually restored to its initial level after the SO2 was cut off. The good reversible sulfur dioxide-resistant performance of PdPtVOx/CZO was associated with the facts: (i) the introduction of SO2 leads to an increase in surface acidity; (ii) V can adsorb and activate SO2, thus accelerating formation of the SOx2− (x = 3 or 4) species at the V and CZO sites, weakening the adsorption of sulfur species at the PdPt active sites, and hence protecting the PdPt active sites to be not poisoned by SO2. EB oxidation over PdPtVOx/CZO might take place via the route of EB → styrene → phenyl methyl ketone → benzaldehyde → benzoic acid → maleic anhydride → CO2 and H2O.

Improved activity and significant SO2 tolerance of Sb–Pd–V oxides on N-doped TiO2 for CB/NOx synergistic degradation

The synergistic degradation of VOCs and NOx that were emitted from the incineration of municipal and medical wastes by a single catalyst is challenging, due to the poor activity at low temperatures, and the SO2 poisoning on the active sites. Herein, N-doped TiO2 (N–TiO2) was used as the support for designing a highly efficient and stable catalyst system for CB/NOx synergistic degradation even in the presence of SO2. The prepared SbPdV/N–TiO2 catalyst, which presented excellent activity and tolerance to SO2 in the CBCO + SCR process, was investigated by a series of characterizations (such as XRD, TPD, XPS, H2-TPR and so on) as well as DFT calculations. The electronic structure of the catalyst was effectively modulated after N doping, resulting in effective charge flow between the catalyst surface and gas molecules. More importantly, the adsorption and deposition of sulfur species and reaction transient intermediates on active centers were restrained, while a new N adsorption center for NOx was provided. Abundant adsorption centers and superior redox properties ensured smooth CB/NOx synergistic degradation. The removal of CB mainly follows the L-H mechanism, while NOx elimination follows both E-R and L-H mechanisms. As a result, N doping provides a new approach to develop more advanced anti-SO2 poisoning CB/NOx synergistic catalytic removal systems for extensive applications.

Effect of Calcination Temperature on the Properties of Nanotitania-Based Extrudates from an Industrial Raw Material

Titanium dioxide is an important material for catalytic reactions as a promoter, support, catalyst, and additive. In this paper, titania extrudates were prepared from industrial raw material by an extrusion method and then calcined at different temperatures. Results show that there are nanostructures with anatase phase from 450o to 850oC because the presence of SO4 2– delays the formation of rutile nucleation up to 950oC,and the morphology is irregular and smooth at 950oC. The SO4 2– ions and crystallinegrowth affect the properties of titania extrudates at various calcination temperatures. At temperatures below 650oC, the effect of SO4 2–removal is more than the effect of crystalline growth on the properties of the extrudates. But at temperatures above 650oC, the effect of crystal growth is dominant because of mobility of atoms, although more sulfate ions are exited. It decreases open pore volume and increases strength and attrition resistance.

Pt/CeMnOx/Diatomite: A Highly Active Catalyst for the Oxidative Removal of Toluene and Ethyl Acetate

Pt nanoparticles and a CeMnOx composite were loaded on the surface of the natural diatomite material to generate the Pt/CeMnOx/diatomite using the redox precipitation and impregnation methods. The physicochemical properties of the catalysts were characterized by means of various techniques. The catalytic properties and resistance to H2O and SO2 of the catalysts were measured for the oxidation of typical volatile organic compounds (i.e., toluene and ethyl acetate). Among all of the as-prepared samples, Pt/CeMnOx/diatomite exhibited the highest catalytic activity: the temperatures (T90%) at a toluene or ethyl acetate conversion of 90% were 230 and 210 °C at a space velocity (SV) of 20,000 mL g−1 h−1, respectively, and the turnover frequency (TOFPt) at 220 °C was 1.04 μmol/(gcat s) for ethyl acetate oxidation and 1.56 μmol/(gcat s) for toluene oxidation. In particular, this sample showed a superior catalytic activity for ethyl acetate oxidation at low temperatures, with its T50% being 185 °C at SV = 20,000 mL g−1 h−1. In addition, the Pt/CeMnOx/diatomite sample possessed good sulfur dioxide resistance during the toluene oxidation process. In the presence of SO2, some of the SO2 molecules were adsorbed on diatomite, which protected the active sites from being poisoned by SO2 to a certain extent. The pathways of ethyl acetate and toluene oxidation over Pt/CeMnOx/diatomite or Pt/CeMnOx were as follows: The C–C and C–O bonds in ethyl acetate are first broken to form the CH3CH2O* and CH3CO* species or toluene is first oxidized to benzaldehyde and benzoic acid, and all of these intermediates are then converted to CO2 and H2O. This work can provide a strategy to develop efficient catalysts with high catalytic activity, durability, low cost, and easy availability under actual working conditions.

Potential of iron-based composites derived from sucrose foam for mercury removal and safe recovery

Although various methods for removal of elemental mercury from gas streams have been proposed, the control of mercury emissions to the environment from anthropogenic sources, mainly coal-fired power plants, remains unresolved in many countries worldwide. Meanwhile, the Minamata Convention and the IED of the European Commission continue to impose restrictions for its control and mitigation. In this work, a new material based on a sucrose foam impregnated with iron oxide nanoparticles has been developed for the adsorption of elemental mercury from flue gases allowing the regeneration of the material and the recovery of elemental mercury. Of the different iron oxides supported on the sucrose foam, αFe2O3 nanoneedles were found to be the most efficient in capturing mercury through a Mars-Maessen mechanism and the forming of HgO. The adsorbents developed proved to be effective in the presence of SO2 and H2O, with the O2 present in the gas playing a key role in the regeneration of the material. From the results found sucrose foam-based αFe2O3 composite could be an attractive alternative to traditional non-regenerable activated carbons, reducing costs and being environmentally sustainable.

Insights into the poisoning mechanisms of zinc compounds on V2O5-WO3/TiO2 catalyst for NH3-SCR: Effect of the anion species

V2O5-WO3/TiO2 is commercial catalyst for controlling NOx emissions from municipal solid waste incineration by NH3 Selective Catalytic Reduction (NH3-SCR). However, the flue gas contains a large amount of zinc compounds, which would lead to the deactivation of the catalyst. Therefore, in this work we studied the effect of different zinc species (ZnSO4, ZnO and ZnCl2) on a V2O5-WO3/TiO2 catalyst, investigating the deactivation mechanism. The different compounds negatively affected the activity in the order ZnCl2 >ZnO>ZnSO4, indicating an important influence of the anions. The characterization results points to the evidence that Zn2+ would interact with the active V-OH and OV structure, reducing the content of active Brønsted acid sites and influencing the V5+⇄V4+ redox cycle, as well as inhibiting the activation of NH3. Cl- would interact with V-OH, possibly forming V-Cl and also suppress the formation and mobility of surface adsorbed oxygen, which further exacerbates the negative effect. On the other hand, SO42- would weaken the poisoning effect of Zn2+ by a strong anion/cation interaction and likely form V-O-SO3OH by reaction with V-OH, which is proposed to be an active Brønsted acid site able to active NH3 in the NH3-SCR reaction. Finally, the introduction of Zn2+ increased the adsorption of NOx species to form a stable and inactive nitro species, the formation of which is inhibited by the presence of SO42-.