SO2 Poisoning Research Articles

Removal of elemental mercury from simulated flue gas by ZSM-5 modified with Mn-Fe mixed oxides

Zeolite (ZSM-5), as a kind of carbon-free sorbent or catalyst, has been widely applied in many fields due to its big surface area, good chemical and thermal stability, and excellent adsorption performance. In this study, Mn-Fe modified ZSM-5 are synthesized via sol-gel approach and employed for elemental mercury (Hg0) removal from simulated flue gas at low temperature. The results show that pure ZSM-5 shows poor mercury capture ability with Hg0 removal efficiency of ~8.5–18.8% at 100–300 °C. Mn or Fe modification can both efficiently enhance the Hg0 removal efficiency of the ZSM-5. The sorbent with Mn/Fe molar ratio of 1:2 exhibits the optimal mercury capture ability with the highest Hg0 removal efficiency near 100% at temperatures of 200 and 250 °C due to the significant synergy effect between Mn2O3 and Fe2O3. The presence of NO has a negligible effect on the Hg0 removal performance of Mn/ZSM-5 and Mn1Fe2/ZSM-5, while the existence of SO2 considerably degrades the Hg0 capture performance of Mn/ZSM-5 owing to competing adsorption and side reactions. Fe addition can protect Mn active sites from SO2 poisoning and thereby enhancing the SO2 resistance of Mn/ZSM-5 to some extent.

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples.

SO2-Resistant Amine-Containing CO2 Adsorbent with a Surface Protection Layer.

Amine-containing solids are promising adsorbents for CO2 capture, but they suffer from irreversible poisoning by the highly acidic SO2 in flue gas. Here, we demonstrate a facile strategy to inhibit SO2 poisoning. We first prepared an amine-containing adsorbent by impregnating polyethyleneimine (PEI) into porous silica. The PEI located at the external surface of the adsorbent was selectively alkylated with epoxide so that amines were fully converted to tertiary amines. As opposed to that onto primary and secondary amines, SO2 adsorption onto tertiary amines is fully reversible. Therefore, during the flue gas adsorption, SO2 is reversibly captured by the tertiary-amine-rich layer and then desulfurized CO2 is adsorbed onto PEI beneath this layer. The resultant adsorbent showed insignificant loss of CO2 adsorption capacity (8.52%) even after 1000 CO2 adsorption-desorption cycles in the presence of 50 ppm SO2, whereas conventional PEI/silica showed severe capacity loss (65.1%) due to irreversible SO2 poisoning.

Byproduct Analysis of SO2 Poisoning on NH3-SCR over MnFe/TiO2 Catalysts at Medium to Low Temperatures

The byproducts of ammonia-selective catalytic reduction (NH3-SCR) process over MnFe/TiO2 catalysts under the conditions of both with and without SO2 poisoning were analyzed. In addition to the NH3-SCR reaction, the NH3 oxidation and the NO oxidation reactions were also evaluated at temperatures of 100–300 °C to clarify the reactions occurred during the SCR process. The results indicated that major byproducts for the NH3 oxidation and NO oxidation tests were N2O and NO2, respectively, and their concentrations increased as the reaction temperature increased. For the NH3-SCR test without the presence of SO2, it revealed that N2O was majorly from the NH3-SCR reaction instead of from NH3 oxidation reaction. The byproducts of N2O and NO2 for the NH3-SCR reaction also increased after increasing the reaction temperature, which caused the decreasing of N2-selectivity and NO consumption. For the NH3-SCR test with SO2 at 150 °C, there were two decay stages during SO2 poisoning. The first decay was due to a certain amount of NH3 preferably reacted with SO2 instead of with NO or O2. Then the catalysts were accumulated with metal sulfates and ammonium salts, which caused the second decay of NO conversion. The effluent N2O increased as poisoning time increased, which was majorly from oxidation of unreacted NH3. On the other hand, for the NH3-SCR test with SO2 at 300 °C, the NO conversion was not decreased after increasing the poisoning time, but the N2O byproduct concentration was high. However, the SO2 led to the formation of metal sulfates, which might inhibit NO oxidation reactions and cause the concentration of N2O gradually decreased as well as the N2-selectivity increased.

Sulfur resistance of Ca-substituted LaCoO3 catalysts in CO oxidation

La1-xCaxCoO3 perovskite catalysts were prepared by using citrate sol-gel method with the various calcium ratios (denoted as La1-xCaxCoO3 (x = 0, 0.1, 0.2, 0.3, 0.4)). The prepared catalysts were poisoned with simulated gas including SO2 to investigate the sulfur resistance of the catalysts. The fresh and sulfur-aged catalysts were then applied to CO oxidation reaction. X-ray diffraction analysis revealed that the catalysts containing calcium also showed perovskite structure. La0.8Ca0.2CoO3 showed the highest CO oxidation activity among the Ca-substituted LaCoO3 catalysts. H2 temperature-programmed reduction indicated that the addition of Ca to LaCoO3 promotes the facile reduction of Co3+, which can explain the higher activity for CO oxidation. Surprisingly, small amounts of SO2 poisoning were observed to promote CO oxidation in Ca-substituted catalysts, although further exposure to SO2 gave rise to the decline of catalytic activity. In addition, Ca-substituted catalysts had higher catalytic activity than LaCoO3 after poisoning with small amounts of sulfur. XPS analysis indicated that Ca-substituted catalysts possessed the less amount of sulfate on the surface than LaCoO3 upon SO2 poisoning. It was summarized that La1-xCaxCoO3 perovskite catalysts had stronger resistance to sulfur poisoning and higher catalytic activity for CO oxidation.

Impact of Hydrothermal Aging on SO2 Poisoning over Cu-SSZ-13 Diesel Exhaust SCR Catalysts

The impact of hydrothermal aging on SO2 poisoning over Cu-SSZ-13 selective catalytic reduction (SCR) catalysts were investigated in this study. The catalyst samples were hydrothermally aged at various temperatures for SO2 poisoning and characterized by SO2 temperature-programmed desorption (SO2-TPD), X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and NH3-TPD. The performance evaluations were also performed to illustrate the impact on SCR activity and oxidation. The results showed that the Cu-SO4-like species decreased in the 750 °C aged sample via copper migration, while they increased in the 850 °C aged sample due to CuOX/CuAlOX formation. The low-temperature SCR activity and oxidation decreased due to sulfur poisoning. For the sulfated sample, however, it was determined that NOX conversion was slightly higher on the mildly hydrothermally aged sample. Furthermore, desulfation is easier for the mildly hydrothermally aged sample but more difficult for the severely hydrothermally age...

Enhancement of NO oxidation activity and SO2 resistance over LaMnO3+δ perovskites catalysts with metal substitution and acid treatment

NOx control by catalytic oxidation combined with wet absorption has been a promising technology for the flue gas treatment of industrial boiler and furnace. LaMnO3+δ perovskites were investigated as catalysts for NO oxidation. The comparison between metal substitution of La and Mn cations was researched. The activity results indicated that La site substitution was more favorable for NO oxidation than Mn site substitution. LaCoMnO exhibited the highest activity in NO oxidation with maximum value of 83.74% at 250 °C. That value further increased to 89.96% after acid etching (LaCoMnO-A), and closely, such high value of 89.78% was achieved at 220 °C. The surface area was significantly improved by acid etching, i.e., from 47.0 m2/g to 212.0 m2/g, Tremendous changes in crystalline structure and morphology were taken place, i.e., perovskites phase disappeared and MnO2 was detected instead; compact amorphous particle morphology was replaced by multiple layer structure. Even more, Mn4+ ions and oxygen vacancies accumulated on the surface were improved. Deservedly, the redox property was enhanced enormously, especially at low temperature. Subsequently, SO2 poisoning tests were conducted at 250 °C under 20 ppm SO2. Interestingly, no decrease was observed for LaCoMnO-A within 480-min SO2 poisoning test, which was totally contrasted with the nearly complete deactivation results of LaCoMnO. In-situ DRIFTS measurements validated nitrate disappeared and replaced by sulfate formation on the catalyst surface. Merely, under low-concentration SO2 atmosphere, the monodentate nitrate and bidentate nitrate were destroyed, while the free nitrates exhibited higher resistance. Overall, the acid etching improved the catalyst resistance to SO2, which may have the potential to apply in the flue gas treatment of low-sulfur and sulfur-free fuel fired boiler and furnace.

The promotion effect of ceria on high vanadia loading NH3-SCR catalysts

A high vanadia loading (5 wt%) catalyst was modified by ceria to improve the NH3-SCR performance. CeVO4 was generated after the addition of ceria to 5 wt% V2O5/TiO2, result not seen in the case of low-loading vanadia samples. CeVO4 presented stable Brønsted acid sites for NH3 adsorption and moderate redox sites for NH3 activation rather than polymeric VOx for the V-based catalyst. These properties effectively suppressed formation of N2O and NO (side reactions). Therefore, ceria preserved the low-temperature activity of V2O5/TiO2 and improved its high-temperature N2 selectivity. Furthermore, ceria promoted the resistance of V2O5/TiO2 to SO2 and H2O poisoning.

The Mo modified Ce/TiO2 catalyst for simultaneous Hg0 oxidation and NO reduction

TiO2 supported CeMo catalyst (CeMo/TiO2) were employed for the first time to simultaneously oxidize elemental mercury (Hg0) and reduce nitrogen monoxide (NO) under simulated SCR atmosphere. The combination of molybdenum oxides and cerium oxides exhibits obvious synergy for Hg0 oxidation and NO reduction. CeMo/TiO2-0.3 catalyst exhibited an excellent Hg0 oxidation and NO reduction efficiencies of over 90% at above 250 °C corresponding to gas hourly space velocity (GHSV) of 119,000 h−1 (NO reduction) and 1,190,000 h−1 (Hg0 oxidation). Brunauer-Emmett-Teller (BET) surface area was not the dominating factor affecting the CeMo/TiO2 performance. Well-dispersion of active species, abundant chemisorbed oxygen and large surface oxygen capacity were responsible for its high catalytic activity. The presence of Hg0 exhibited a negligible effect on NO reduction. Low-concentration of NO inhibited the Hg0 oxidation while a relatively high concentration had a promotional effect inversely due to abundant NO2. NH3 consumed surface oxygen and competed to adsorb with Hg0 resulting in the deactivation of Hg0 oxidation while an excellent recovery was observed after simultaneous cutting off NH3 and introduction of O2. In addition, CeMo/TiO2-0.3 catalyst also presented an excellent resistance to SO2 and H2O poisoning and a good stability and recyclability. The possible mechanism for simultaneous NO reduction and Hg0 oxidation was proposed for CeMo/TiO2 catalysts.

Single-phase SO2-resistant to poisoning Co/Mn-MOF-74 catalysts for NH3-SCR

Single-phase Co/Mn-MOF-74 solid materials were synthesized successfully via the hydrothermal method. The effect of Co/Mn atom ratio on the structure of Co/Mn-MOF-74 solids and their catalytic activity for low-temperature NH3-SCR of NOx were investigated. Very high NO conversion values (>96.0%) at 180–240 °C were obtained using the Mn0.66Co0.34-MOF-74 chemical composition (optimal content of Co). Furthermore, Mn0.66Co0.34-MOF-74 showed outstanding resistance to SO2 poisoning and the incorporation of Co was shown to cause the weakening of the SO2 adsorption strength on the catalyst surface, thus to enhance catalyst's SO2 resistance to poisoning. These features were probed by in situ DRIFTS and catalytic performance studies. The present work suggests that Mn0.66Co0.34-MOF-74 could be likely considered as a prospective industrial NH3-SCR NOx control catalyst.

Synthesis of novel MnOx@TiO2 core-shell nanorod catalyst for low-temperature NH3-selective catalytic reduction of NOx with enhanced SO2 tolerance

In this study, a MnOx@TiO2 core-shell catalyst prepared by a two-step method was used for the low-temperature selective catalytic reduction of NOx with NH3. The catalyst exhibits high activity, high stability, and excellent N2 selectivity. Furthermore, it displays better SO2 and H2O tolerance than its MnOx, TiO2, and MnOx/TiO2 counterparts. The prepared catalyst was characterized systematically by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman, BET, X-ray photoelectron spectroscopy, NH3 temperature-programmed desorption and H2 temperature-programmed reduction analyses. The optimized MnOx@TiO2 catalyst exhibits an obvious core-shell structure, where the TiO2 shell is evenly distributed over the MnOx nanorod core. The catalyst also presents abundant mesopores, Lewis-acid sites, and high redox capability, all of which enhance its catalytic performance. According to the XPS results, the decrease in the number of Mn4+ active centers after SO2 poisoning is significantly lower in MnOx@TiO2 than in MnOx/TiO2. The core-shell structure is hence able to protect the catalytic active sites from H2O and SO2 poisoning.

Promoting Effect of Organic Ligand on the Performance of Ceria for the Selective Catalytic Reduction of NO by NH3

AbstractTwo CeO2 catalysts were fabricated by dry ball milling in the absence or presence of organic ligand, denoted as CeO2‐A and CeO2‐B, respectively, and tested for selective catalytic reduction of NO by NH3 (NH3‐SCR). It was found that the CeO2‐B catalyst exhibited high NH3‐SCR activities as well as high SO2 and H2O resistance. The characterizations of nitrogen adsorption (BET), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), Raman spectroscopy, temperature‐programmed reduction (H2‐TPR), temperature‐programmed desorption (SO2‐TPD) and X‐ray photoelectron spectroscopy (XPS) revealed that the addition of adipic acid in the synthetic procedure leaded to a high reducibility of cerium species and a special surface microstructure, including relative high surface defects and hierarchical pore structure of the CeO2 catalyst, which played important roles in enhancing NH3‐SCR performance. Meanwhile, the interaction between SO2 and CeO2 under different condition was investigated in detail by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) and SO2‐TPD. The data suggested that the high resistance to SO2 poisoning of CeO2‐B could be explained by a low amount of sulfur species formation and a low speed transformation of sulfites to sulfates on the ceria catalyst due to its special surface microstructure.

The promoting effect of CeO2@Ce-O-P multi-core@shell structure on SO2 tolerance for selective catalytic reduction of NO with NH3 at low temperature

A series of CeO2@Ce-O-P “multi-core@shell” catalysts were synthesized in this paper for selective catalytic reduction (SCR) of NO with NH3. The experimental results had showed that CeO2@Ce-O-P-30:3 yielded best SO2 tolerance of an over 70% deNOx efficiency at 250 °C in the presence of 100 ppm SO2 for 20 h, which was much higher compared to pure Ce-O-P and CeO2 samples. Further characterization results indicated that Ce-O-P coating layer could somewhat inhibit sulfur depositing on the catalysts during SCR reaction in the presence of SO2, thereby protecting the active sites from SO2 poisoning. Especially, O2-TPD results illustrated that a great amount of active oxygen species were retained on used CeO2@Ce-O-P catalyst after a long term reaction. The synergetic effect of “multi-core@shell” structure could be attributed to such enhanced performances. The “core” CeO2 devoted abundant active oxygen sites to fulfill the SCR reaction. And the “shell” Ce-O-P could not only provide acid sites, but also protect the active oxygen species by avoiding the over-adsorption of SO2 on the catalyst. This work could provide a new way to increase the sulfur resistance for low temperature SCR catalysts.

Effect of alumina incorporation on the sulfur tolerance of the dual-catalyst aftertreatment system for reduction of nitrogen oxides under lean conditions

Presence of sulfur or sulfur additives in natural gas lead to the formation of sulfur dioxide in the exhaust stream of natural gas-fired lean-burn engines. The sulfur tolerance and hydrothermal stability of the dual-catalyst aftertreatment system comprising a reduction catalyst (palladium supported on sulfated zirconia- Pd/SZ) and an oxidation catalyst (cobalt oxide supported on ceria- CoOx/CeO2) for NOx reduction under lean-burn conditions has been tested under simulated engine exhaust conditions. Alumina-incorporated Pd/SZ (Pd/SZ(Alumina)) reduction catalyst as part of the dual catalyst bed demonstrated superior sulfur tolerance in the presence of 5 ppm SO2 in the feed. The ratio of the reduction to oxidation catalyst was also seen to affect the hydrothermal stability under wet conditions with SO2 in the reaction medium. The effect of hydrocarbon and water concentration in the reaction mixture on the sulfur tolerance of the dual-catalyst bed was studied. Increasing the reaction temperature from 450 °C to 500 °C demonstrated very stable NOx conversion and improved CH4 conversions when the dual-catalyst bed was kept on-stream for 40 h−1. X-ray photoelectron spectroscopy on samples poisoned with SO2 ex-situ revealed the deposition of surface sulfates on the Pd/SZ catalyst samples and a combination of sulfates and sulfites on the CoOx/CeO2 on treatment with SO2. The presence of alumina in the Pd/SZ sample protects the support from SO2 poisoning as the oxidation state of the zirconia support remained largely unchanged on poisoning while in the CoOx/CeO2 sample, sulfur poisoning likely affects the cerium redox cycle (Ce3+-Ce4+). 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) revealed redistribution of the octahedral and tetrahedral Al-O coordination on SO2 poisoning. Due to association with deposited sulfates on the catalyst, shielding effect on the Al nuclei resulted in an increased octahedral Al-O coordination in the poisoned sample.

NOxRemoval over V2O5/WO3–TiO2Prepared by a Grinding Method: Influence of the Precursor on Vanadium Dispersion

V2O5/WO3–TiO2 (VWT) catalysts for selective catalytic reduction (SCR) of NOx removal were prepared by a mechanical grinding method using different vanadium precursors. The SCR performances were evaluated in simulated flue gas and explained through characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, H2 temperature-programmed reduction, and in situ diffuse reflectance Fourier transform spectroscopy. VO(acac)2–VWT catalyst prepared using a vanadyl acetylacetonate (VO(acac)2) precursor exhibited the highest catalytic activity and excellent resistance to SO2 and H2O poisoning in 200–400 °C compared to the catalysts obtained using other precursors. The VO(acac)2 precursor could enrich V on the surface remarkably and promote the formation and dispersion of polymeric vanadia species. Furthermore, a relatively high percentage of low-valent vanadium atoms were found on the VO(acac)2–VWT surface, facilitating electron transfer between V4+ and V5+. Surface-adsorbed NH3 species on VO(acac)2–VWT were much more reactive. The initial geometry of vanadium precursors determined the tendency of V to accumulate and further influenced the dispersion and final form of V species.

Denitrification performance of non-pitch coal-based activated coke by the introduction of MnOx–CeOx–M (FeOx, CoOx) at low temperature

Modified activated coke was prepared by the introduction of MnOx, CeOx, and M (FeOx, CoOx) into non-pitch coal-based activated coke (NPAC) using a novel non-pitch binder. The modified non-pitch coal-based activated coke was characterized in detail by N2 physical adsorption, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, and its catalytic activity was examined by the selective catalytic reduction of NO with NH3 at low temperature. In addition, the SO2 and H2O tolerance was investigated. The results indicated that compared to MnOx–CeOx–4.39, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibit considerably higher catalytic activities while simultaneously maintaining NOx removal rates of 78.98% and 77.85%, respectively, at 150°C. The high catalytic performance of Mn–Ce–Co/NPAC-a and Mn–Ce–Fe/NPAC-a is related to several better properties compared to MnOx–CeOx–4.39, namely, considerably higher specific surface areas and percentages of Oα/(Oα+Oβ+Oγ) and Ce3+/(Ce3++Ce4+), more easily reduced of Mn species, high reducibility, and more acidic sites. Furthermore, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibited specific resistance to SO2 and H2O poisoning, and the SO2 deactivation mechanism was proposed.

Metal-organic framework loaded manganese oxides as efficient catalysts for low-temperature selective catalytic reduction of NO with NH3

A mild in-situ deposition method was used to fabricate Mn-based catalysts on a UiO-66 carrier for the selective catalytic reduction of NO by NH3 (NH3-SCR). The catalyst with 8.5 wt-% MnO x loading had the highest catalytic activity for NH3-SCR with a wide temperature window (100–290 °C) for 90% NO conversion. Characterization of the prepared MnO x /UiO-66 catalysts showed that the catalysts had the crystal structure and porosity of the UiO-66 carrier and that the manganese particles were well-distributed on the surface of the catalyst. X-ray photoelectron spectroscopy analysis showed that there are strong interactions between the MnO x and the Zr oxide secondary building units of the UiO-66 which has a positive effect on the catalytic activity. The 8.5 wt-% MnO x catalyst maintained excellent activity during a 24-h stability test and exhibited good resistance to SO2 poisoning.

V2O5-decorated Mn-Fe/attapulgite catalyst with high SO2 tolerance for SCR of NOx with NH3 at low temperature

Fe-based catalysts were widely reported with high N2 selectivity in the NH3-SCR reaction in recent years. Unfortunately, the Fe-based catalysts usually exhibit poor NOx conversion at low temperature. In order to solve this problem, MnO2 was chosen to enhance the low temperature activity of the catalyst. In this work, V2O5-decorated Mn-Fe/attapulgite (V@Mn-Fe/ATP) with high SO2 tolerance were prepared by impregnation and sol-gel methods and used for selective catalytic reduction of NO by NH3 (NH3-SCR). In addition, γ-Fe2O3/ATP and Mn-Fe/ATP were also prepared for comparison with the V@Mn-Fe/ATP. The as-prepared catalysts were characterized by XRD, TEM, BET, H2-TPR, NH3-TPD, and XPS. It could be deduced from TEM, XRD, and BET, the specific surface area was improved due to a uniform V2O5 layer formed on the Mn-Fe/ATP surface. The results of XPS and NH3-TPD illustrated that the coating of V2O5 could also enhance the amount of surface chemisorbed oxygen and acidic sites, which play significant influence on oxidation of NO and NH3 absorption during NH3-SCR and are also beneficial to increase SCR reaction rates. Moreover, the test of SO2 tolerance and stability demonstrated that the V2O5 layer could effectively inhibit SO2 poisoning and improve the stability of catalysts. Therefore, the V@ Mn-Fe/ATP was proved to be an excellent catalyst for NH3-SCR.

Mechanism of Ce promoting SO2 resistance of MnO x /γ-Al2O3: An experimental and DFT study

Various physico-chemical techniques and theoretical chemistry computations are used to obtain a deep insight into the mechanism of Ce improving SO2 resistance of the catalyst Mn0.4Ce x /Al2O3 (x stands for the molar ratio of Ce : Al). Theoretical computation with density functional theory (DFT) shows that Ce modification enhances the adsorption energy of SO2 adsorbed on Ce surrounding, resulting in the preferential adsorption of SO2 on Ce surrounding. It protects the surface Mn from SO2 poisoning, leading to a better SO2 resistance. FT-IR and TG results are in good accordance with DFT results. FT-IR results suggest that absorption peaks related to SO4 2− cannot be detected in Mn0.4Ce0.12/Al2O3. Moreover, TG results show that weight loss peaks due to sulfated MnO x decomposition disappears after Ce addition. Therefore, Ce modification inhibits sulfates formation on active components lead to a better resistance to SO2 of Mn0.4Ce0.12/Al2O3.

Application of sodium carbonate prevents sulphur poisoning of catalysts in automated total mercury analysis

Analysis of high sulphur-containing samples for total mercury content using automated thermal decomposition, amalgamation, and atomic absorption spectroscopy instruments (USEPA Method 7473) leads to rapid and costly SO2 poisoning of catalysts. In an effort to overcome this issue, we tested whether the addition of powdered sodium carbonate (Na2CO3) to the catalyst and/or directly on top of sample material increases throughput of sulphur-impregnated (8–15wt%) activated carbon samples per catalyst tube. Adding 5g of Na2CO3 to the catalyst alone only marginally increases the functional lifetime of the catalyst (31±4g of activated carbon analyzed per catalyst tube) in relation to unaltered catalyst of the AMA254 total mercury analyzer (17±4g of activated carbon). Adding ≈0.2g of Na2CO3 to samples substantially increases (81±17g of activated carbon) catalyst life over the unaltered catalyst. The greatest improvement is achieved by adding Na2CO3 to both catalyst and samples (200±70g of activated carbon), which significantly increases catalyst performance over all other treatments and enables an order of magnitude greater sample throughput than the unaltered samples and catalyst. It is likely that Na2CO3 efficiently sequesters SO2, even at high furnace temperatures to produce Na2SO4 and CO2, largely negating the poisonous impact of SO2 on the catalyst material. Increased corrosion of nickel sampling boats resulting from this methodological variation is easily resolved by substituting quartz boats. Overall, this variation enables an efficient and significantly more affordable means of employing automated atomic absorption spectrometry instruments for total mercury analysis of high-sulphur matrices.