Catalytic Reduction Of SO Research Articles

Capture and Catalytic Reduction of SO2 with H2 to Elemental Sulfur by Novel Guanidinium-Based Deep Eutectic Solvents

Capture and Catalytic Reduction of SO₂ with H₂ to Elemental Sulfur by Novel Guanidinium-Based Deep Eutectic Solvents

Effects of Cobalt-Doped Modification on the Catalytic Reduction of SO2 with CO over an Iron/BFS Catalyst

To realize high-value sulfur recovery and decrease the reaction temperature, a cobalt-doped modified iron-based catalyst was prepared from blast furnace slag (BFS), which is a byproduct of steelmaking. The effects of the carrier and active components on the catalytic reduction performance were studied, and the mechanism of the optimized modification to promote catalytic reduction was explored. When the mass ratio of cobalt tetroxide, ferric oxide, and the carrier in the catalyst was 4:15:81, the temperature required for the reaction was reduced to 400 °C, and the SO2 conversion rate and average sulfur yield were maintained above 90 and 80% within 2 h, respectively. The results of an in situ diffuse reflectance infrared Fourier-transform spectroscopy experiment and density functional theory calculations revealed that the catalytic mechanism followed both the redox route and the cosine intermediate route. The cobalt-doped modification increased the intermediate acidic sites on the catalyst surface and widened the adsorption temperature range of the catalyst, thus positively promoting the catalytic reaction.

Simultaneous catalytic reduction of SO2 and NO from flue gas using H2S as a reductant at low temperatures

High-efficiency simultaneous removal of NO and SO2 in flue gas can be realized by catalytic reduction with H2S on CeO2–AT catalyst in the low temperature range of 240 to 280 °C.

Experimental Study on Catalytic Reduction of SO<sub>2</sub> by Rare Earth Compound

Compared with a great deal of traditional desulphurization crafts, the catalytic reduction of SO2 with CO to elemental sulfur is considered to be the best technology for the removal of SO2 from flue gas. Adding rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. By means of dipping CeO2, La2O3 and their mixture, whose carriers are allγ-Al2O3, are used as the catalyst for the reduction of SO2 by CO. The activation process of this catalyst without O2 was investigated. The result shows that the rare earth oxide mixture composing of CeO2 and La2O3, as the catalyst for the reduction of SO2 by CO, can remove SO2 mostly without O2.

Microwave Catalytic Conversion of SO 2 and NO x over Cu/zeolite

Abstract: Microwave catalytic technology is a promising technology for flue gas treatment. Cu/zeolite was used as catalyst for microwave catalytic desulfurization and denitrification and for microwave catalytic reduction of SO 2 and NOx with ammonium bicarbonate (NH 4 HCO 3 ) as a reducing agent. Microwave catalytic desulfurization and denitrification efficiency achieved 76.1 and 81.8% separately. The reaction efficiency of microwave catalytic reduction of SO 2 and NO x could be up to 99.8 and 92.8% respectively. The physico-chemical properties of Cu/zeolite catalysts were characterized by X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller measurements (BET), X-ray photoelectron spectrum analysis (XPS), scanning electron microscopy (SEM).The XPS results indicate that sulfide (SO4 2- ), element sulfur (S 0 ) and NH 4 + species exist on the catalyst surface after the reaction. Microwave catalytic SO 2 and NO x removal follows Langmuir — Hinshelwood(L-H) kinetics. Key words: Simultaneous desulfurization & denitrification; Microwave catalytic technology; Cu/zeolite; Characterization

Catalytic reduction of SO 2 over Sn–Zr based catalysts for DSRP under high pressure

The catalytic activity of Sn–Zr based catalysts and the production behavior of COS during SO 2 reduction were investigated for the catalytic reduction of SO 2 under high pressure condition in this study. The SnO 2, ZrO 2 and SnO 2–ZrO 2 used as the catalysts were prepared by the precipitation and co-precipitation methods. The activity tests for the Sn–Zr based catalysts were carried out in the range of 200–450 °C at atmospheric pressure and 20 atm. CO was also used as the reducing agent for the reduction of SO 2. The catalytic activity and a surface area of the SnO 2–ZrO 2 prepared by the co-precipitation methods were higher than that of the SnO 2 and SnO 2–ZrO 2 catalysts prepared by the physical mixing. It was concluded that the surface area of SnO 2–ZrO 2 catalyst prepared by the co-precipitation increased due to the formation of the lattice defects. A high yield of elemental sulfur was also maintained for 50 h in the durability test. Carbonyl sulfide is produced by the reaction between CO and the elemental sulfur produced during the reduction of SO 2, and was also produced by the gas–solid reaction between the metal sulfide and CO. The selectivity of COS was high at the intermediate level of conversion of SO 2. Since the vapor pressure of elemental sulfur decreased with increasing pressure, the production of COS was reduced to a greater extent at the high SO 2 conversion observed at high pressure. From these results, it was confirmed that SnO 2–ZrO 2 is a suitable catalyst for the catalytic reduction of SO 2 at high pressure.

Reduction of SO 2 to elemental sulfur over rare earth-iron catalysts

With coal gas as a reducing agent, the catalytic reduction of SO 2 to sulfur in the flue gas produced in metallurgical processes was studied over catalysts of rare earth-Fe/Al 2O 3 (REFe/Al 2O 3). The catalytic activity of the REFe/Al 2O 3 catalyst on the reduction of SO 2 to sulfur was investigated based on kinds and the contents of rare earths and different preparation method of the catalyst. Additionally, the mechanism of this catalytic reduction reaction was also explored. Results showed that different rare earth imposed different effect on the activity of the Fe/Al 2O 3 catalyst. Especially, the addition of Sm and Dy greatly improved the catalytic activity of Fe/Al 2O 3. The yield of sulfur over SmFe/Al 2O 3 was increased to 86.62% at 360 °C, which was 40.5% higher than that over Fe/Al 2O 3 at the same temperature; and the sulfur yield over DyFe/Al 2O 3 was increased to 91.62% at 400 °C, 26.4% higher than that over Fe/Al 2O 3. The catalytic activity of REFe/Al 2O 3 was somehow dependent on the content of rare earth. For SmFe/Al 2O 3, the content of Sm was optimized to be about 1.0 wt.%. The rare earth catalyst prepared with different methods also showed varied activity. The sulfur yield over rare-earth transition metal catalysts follows the order: Sm and iron solution mixing impregnation>Sm first, then iron solution impregnation>iron first, then Sm solution impregnation. The reaction mechanism of SO 2 reduction to sulfur with coal gas was proposed to be an intermediate mechanism.

The effect of H2O on the reduction of SO2 and NO by CO on La2O2S

The effect of H2O on the catalytic reduction of SO2 and NO on La2O2S was studied using temperature-programmed reaction coupled with fast mass spectrometry, powder X-ray diffraction and X-ray photoelectron spectroscopy. It is found that La2O2S can be completely and irreversibly deactivated in the presence of H2O at 700°C when NO/SO2 is sufficiently high (∼1.0). This is caused by the formation of a layer of inactive and stable La2O2SO4 on the oxysulfide. When NO is absent or NO/SO2 is low (∼0.4), H2O inhibits the reduction and shifts the selectivity from sulfur to H2S. While the causes of the deactivation can be attributed to the Reverse Claus Reaction between H2O and sulfur in the oxysulfide, the competitive hydrolysis of the COS intermediate and the competitive adsorption of H2O, the shift in selectivity to H2S is attributable to the former two factors.

Optimization of Operating Conditions for the Catalytic Reduction of SO 2 Produced from Regeneration Process in Hot Gas Desulphurization

In order to remove hydrogen sulphide from a synthetic gas produced in a gasifier, a hot gas desulphurization (HGD) system was set up in this study. HGD process in the IGCC consisted of sulphidation process, regeneration process and direct sulphur recovery process. The fluidized-bed reactor system for coal gas desulphurization and the fixed-bed reactor system for catalytic SO2 reduction were integrated and the optimum operating conditions for the direct sulphur recovery process were investigated in this study. Zinc-based sorbents (ZZF) were used for the hydrogen sulphide removal. The sulphur content of the gasified coal gas was reduced from 10000 parts per million to several ppmv in a fluidized-bed reactor. The concentration of SO2 in the exiting gas from the reactor during regeneration process was about 3 vol%. The produced SO2 in regeneration process was converted to elemental sulphur in the direct sulphur recovery process (DSRP). The catalytic reduction of SO2 was carried out on the Sn–Zr based catalysts with the simulated coal gas containing H2 and CO as reducing agents. The test for DSRP was performed in the temperature range of 300–550°C. Space velocity (GHSV) was 10000 cm3 g-cat h−1 and the mole ratio of reductants (H2 + CO) to SO2 was 2.5. All three unit processes in HGD, sulphidation, regeneration and DSRP, were integrated in this study. In the integrated tests, it was confirmed that the unreacted oxygen in the regeneration process caused a secondary reaction in DSRP. In order to prevent the secondary reaction, the unreacted oxygen was minimized during the regeneration process. Its amount was maintained less than 0.1 vol% at conditions of the 3 vol% concentration of oxygen in the entering gas to the reactor at 6508C. Around 92% conversion and 75% elemental sulphur yield were obtained in the DSRP test integrated with the desulphurization in a lab-scale fluidized-bed unit.

Catalytic Reduction of SO2 with CO over Supported Iron Catalysts

Iron oxides supported on several types of carriers (γ-Al2O3, HZSM-5, SiO2, and MgO) were investigated for the catalytic reduction of SO2 by CO. The catalytic tests show that the activity of the catalysts followed the order Fe2O3/γ-Al2O3 > Fe2O3/HZSM-5 ≫ Fe2O3/SiO2 > Fe2O3/MgO. The X-ray diffraction analysis characterization of the presulfided catalysts revealed that FeS2 formation was greatly dependent on the acidic nature of the supports, with an evident FeS2 phase detected on both γ-Al2O3 and HZSM-5, in contrast with Fe7S8 formed on SiO2 and MgO. Presulfidation with a reacting gas mixture above 500 °C was necessary for obtaining a high activity because of the formation of active-phase FeS2 during this process. The catalytic activity correlated well with the sulfidation degree of Fe2O3, which is mainly dependent on the acidic nature of the support and the choice of the presulfidation conditions. When the Fe content was at 20 wt %, under the optimal feed compositions (CO/SO2 = 2:1), the Fe2O3/γ-Al2O3 cata...

Nanosized CeO2-supported metal oxide catalysts for catalytic reduction of SO2 with CO as a reducing agent

Nanosized CeO2 was synthesized by sol–gel method and used as the support to prepare six kinds of supported metal oxide catalysts by incipient wetness impregnation method. These catalysts were investigated for the catalytic reduction of SO2 to elemental sulfur with CO as a reducing agent. Experimental results indicate that Cr2O3/nano-CeO2 was the most active catalyst. Using this catalyst, a kinetic study was performed on the reduction of SO2 and the optimal feed ratio of CO/SO2 was found to be 2.5/1, and low concentrations of SO2 and CO provide a high SO2 conversion and sulfur yield. We also found that the catalyst presulfided by CO + SO2 exhibits a higher performance than those pretreated with CO, SO2 or He. The discrepancy in the stability and activity resulted in the pretreatment has been rationally explained. The temperature-programmed desorption patterns of SO2 and CO illustrate that Cr2O3/nano-CeO2 can adsorb and desorb SO2 and CO more easily than can other catalysts. These results may properly explain why Cr2O3/nano-CeO2 has a higher activity for the reduction of SO2.

Supported transition-metal oxide catalysts for reduction of sulfur dioxide with hydrogen to elemental sulfur

This work is for the purpose to find a high performance catalyst for the catalytic reduction of SO 2 with H 2 as a reducing agent. NiO/γ-Al 2O 3 catalyst was found to be the most active catalyst among the seven γ-Al 2O 3-supported metal-oxide catalysts tested. With NiO as the active species, of the supports tested, γ-Al 2O 3 was the most suitable one and the optimal Ni content was 16 wt%. Using this NiO/γ-Al 2O 3 catalyst, we found that the optimal feed ratio of H 2/SO 2 is 2:1 and the catalyst presulfided with H 2 + H 2S exhibits a higher performance than that pretreated with H 2 or He. XRD patterns reveal that the nickel oxide experienced a transformation to Ni 3S 2 and NiS, and then to NiS 2, the most active nickel sulfide, during the reaction process. The reason for the highest catalyst activity of 16 wt% Ni was attributed to the largest amount of NiS 2. Water vapor in the feed gas reactant caused inhibition of catalyst activity, whereas H 2S promoted the reduction of SO 2. These phenomena were rationalized with the aid of Claus reaction.

Separate/simultaneous catalytic reduction of sulfur dioxide and/or nitric oxide by carbon monoxide over titanium–tin solid solution catalysts

Titanium–tin solid solutions prepared by coprecipitation were studied for the separate and simultaneous catalytic reduction of SO 2 and/or NO by CO. Physicochemical characterizations of the solid solutions before and after reactions with different SnO 2 contents were conducted to disclose the reaction mechanism by means of XRD, CO–TPR, XPS and transient MS techniques. It is found that TiO 2–SnO 2 solid solutions were very active towards the reduction of SO 2 by CO at a low temperature and space velocity. There existed a strong synergistic promoted effect, which can be explained based on an enhanced redox mechanism proposed in the work. Furthermore, TiO 2–SnO 2 solid solutions would show a pronounced increase in catalytic activity during the reduction of NO by CO after the catalysts finished SO 2+CO reactions, or by introducing SO 2 into the reaction feed. This promoting effort is due to the formation of tin sulfide species as a product of the reduction of SO 2 by CO on the catalyst surface. A NO decomposition mechanism with the formation of SO 2 by-product was proposed. The produced SO 2 was in situ catalytically reduced to sulfur to regenerate tin sulfide. Lastly, simultaneous catalytic reduction of SO 2 and NO using CO as a reducing agent was carried out on TiO 2–SnO 2 solid solution catalysts. Experimental results showed that at a temperature above 350 °C, SO 2 and NO conversions are greater than 91 and 99%, respectively.

Catalytic reduction of SO2 over supported transition-metal oxide catalysts with C2H4 as a reducing agent

This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO2 with C2H4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C2H4/SO2, and pretreatment are all important factors affecting catalyst activity. Fe2O3/γ-Al2O3 was found to be the most active catalyst among six γ-Al2O3-supported metal oxide catalysts tested. With Fe2O3 as the active species, of the supports tested, CeO2 is the most suitable one. Using this Fe2O3/CeO2 catalyst, we found that the optimal Fe content is 10wt.%, the optimal feed ratio of C2H4/SO2 is 1:1, and the catalyst presulfidized by H2+H2S exhibits a higher performance than those pretreated with H2 or He. Although the feed concentrations of C2H4:SO2 being 3000:3000ppm provide a higher conversion of SO2, the sulfur yield decreases drastically at temperatures above 300°C. With higher feed concentrations, maximum yield appears at higher temperatures. The C2H4 temperature-programmed desorption (C2H4-TPD) and SO2-TPD desorption patterns illustrate that Fe2O3/CeO2 can adsorb and desorb C2H4 and SO2 more easily than can Fe2O3/γ-Al2O3. Moreover, the SO2-TPD patterns further show that Fe2O3/γ-Al2O3 is more seriously inhibited by SO2. These findings may properly explain why Fe2O3/CeO2 has a higher activity for the reduction of SO2.

Catalytic reduction of SO 2 during combustion of typical Chinese coals

The catalytic effects of doping agents on SO 2 emission as well as the coal combustion behavior were investigated by thermogravimetry. All experiments were carried out in a flowing air atmosphere at a heating rate of 20 or 30 °C/min up to 1000 °C. The doping agents employed were NaCl, CaCl 2, FeCl 3, FeCl 2 and Fe 2O 3. The experimental results show that the agents added in coal reduce SO 2 emission of coal, with CaCl 2 being the most effective. The doping agents work with different mechanisms. The catalysis of NaCl, CaCl 2, and Fe 2O 3 promotes the reactions between SO 2 and the minerals in coal, and enhances the sulfur retention capacity of coal ash, thus decreasing SO 2 concentration in flue gas. They have weak effects on the combustion behavior of the coal. FeCl 3 and FeCl 2 have strong effects on coal combustion behaviour. They accelerate the combustion and improve the ignition of the char subsequently formed, increasing SO 2 concentration in flue gas in the region from 300 to 520 °C. However, they reduce the total amount of SO 2 emission during combustion. The reduction of SO 2 yield by FeCl 3 and FeCl 2 mainly results from the Fe 2O 3 created from them at high temperatures.

Supported Transition-Metal Oxide Catalysts for Catalytic Reduction of SO2 with CO as a Reducing Agent

Performances of supported transition-metal oxide catalysts in the catalytic reduction of SO2 with CO as a reducing agent were investigated. According to our study, Fe2O3/γ-Al2O3 was found to be the most active catalyst among eight γ-Al2O3-supported catalysts tested. With Fe2O3 as the active species, CeO2 is the most suitable support. Using Fe2O3/CeO2, the best catalyst, the optimal feed ratio of CO/SO2 is 3:1 and provides the highest yield of elemental sulfur and a higher conversion of SO2. The catalyst presulfied by CO + SO2 exhibits a higher performance than those pretreated with CO, H2, or He. The desorption patterns of CO temperature-programmed desorption (TPD) indicate that Fe2O3/CeO2 is more easily reduced by CO than Fe2O3/γ-Al2O3, while the SO2-TPD patterns reveal that Fe2O3/γ-Al2O3, which is more seriously inhibited by SO2 than Fe2O3/CeO2, adsorbs more strongly a larger amount of SO2. These two facts might be the predominant reasons why Fe2O3/CeO2 has a far higher activity and stability.

Catalytic Reduction of SO<sub>2</sub> by CO on Sulfided CoMo/ Al<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Catalysts

Catalytic Reduction of SO<sub>2</sub> by CO on Sulfided CoMo/ Al<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Catalysts

Ceria-based catalysts for the recovery of elemental sulfur from SO 2-laden gas streams

The catalytic reduction of SO 2 to elemental sulfur by CO or CH 4 over ceria-based catalysts under demanding operating conditions is reported in this paper. Cu- or Ni-containing ceria catalysts have been shown before to be highly active and selective for SO 2 reduction by CO in dry gas streams or in the presence of low amounts of H 2O. In this work, the activity/selectivity of 10 at.%La-doped ceria, Ce(La)O x , and Cu- or Ni-containing Ce(La)O x for the (SO 2+CO) reaction was tested in gas streams containing 10–45 mol%H 2O at high space velocities (>80,000 h −1). The addition of 5 at.% (∼2.5 wt.%) copper or nickel significantly improved the low-temperature (<500°C) reactivity of Ce(La)O x . This was correlated with the improved reducibility of ceria in the metal-ceria catalysts and the ensuing low-temperature activity for the water-gas-shift (WGS) reaction. The combined reduction of SO 2 and NO by CO was also studied in this work over the same catalysts. In dilute gas mixtures containing 0.1–1.0 mol%SO 2 and NO, stoichiometric amount of CO and in the presence of 40%H 2O, the NO presence in the feed gas enhances both the SO 2 conversion and the elemental sulfur yield. At 550°C, in the presence of NO, SO 2 conversion and sulfur yield over the 5%Ni-Ce(La)O x catalyst were 0.94 and 0.77, respectively, the NO conversion to N 2 was complete, and the CO 2 produced was the sum of the SO 2 and NO reduction reactions by CO. Ceria-based materials are also active for SO 2 reduction by methane to elemental sulfur at temperatures higher than 550°C. The addition of Cu or Ni has a different effect on the sulfur selectivity of ceria under fuel-rich conditions. The Cu-ceria system is a complete oxidation catalyst to a much higher temperature than Ni-ceria. Over Ni-CeO 2, dissociation of methane begins at <550°C, and side reactions favor H 2S production over elemental sulfur. However, the 5 at.%Ni-Ce(La)O x catalyst showed remarkable resistance to carbon deposition, both in the SO 2-methane reaction as well as in partial oxidation of methane by O 2 to synthesis gas with a 2:1 H 2:CO ratio. This is attributed to the high dispersion of nickel in this catalyst and the fast rate of oxygen supply from ceria to the nickel interface. Catalysts were characterized by temperature-programmed-reduction, XPS and STEM/EDS.

Catalytic conversion of CO, NO and SO2 on the supported sulfide catalyst: I. Catalytic reduction of SO2 by CO

Catalytic reduction of SO2 to elemental sulfur by CO has been systematically investigated over γ-Al2O3-supported sulfide catalysts of transition metals including Co, Mo, Fe, CoMo and FeMo with different loadings of the metals. The sulfided CoMo/Al2O3 exhibited outstanding activity: a complete conversion of SO2 was achieved at a temperature of 300°C. The reaction proceeds catalytically and consistently over time and most efficiently at a molar feed ratio CO/SO2=2. A precursor CoMo/Al2O3 oxide which experienced sulfurization through the CO–SO2 reaction yielded a working sulfide catalyst having a yet lower activity than the CoMo catalyst sulfided before reaction (pre-sulfiding). The catalytic activity of various metal sulfides decreased in order of 4% Co 16% Mo>4% Fe15% Mo>16% Mo≥25% Mo>14% Co≥4% Co>4% Fe. A DRIFT study showed that CO adsorbs exclusively on CoMo phase and that SO2 predominantly on γ-Al2O3. It is suggested that the Co–Mo–S structure is more adequate than the other metal-sulfur structures for the formation of a carbonyl sulfide (COS) intermediate because of the proper strength of metal–sulfur bond, and catalytically works with γ-Al2O3 for the COS–SO2 reaction.

Direct reduction of SO 2 to elemental sulfur by methane over ceria-based catalysts

The catalytic reduction of SO 2 to elemental sulfur by methane was studied over ceria-based catalysts. Both La-doped and undoped ceria were found to catalyze the SO 2 reduction by CH 4 in the temperature range of 550–750°C at atmospheric pressure and with feed gases containing a molar ratio of CH 4/SO 2 = 0.5–3. At temperatures below ∼550°C, the catalyst surface is capped by SO 2. The reaction light-off coincides with the threshold temperature for sulfate decomposition. Various SO 2/CH 4/H 2O gas mixtures were used to study the catalyst activity and selectivity to elemental sulfur. The incorporation of nickel and copper improves the wet activity of Ce(La)Ox catalysts. Also, the addition of a low amount (5 at.%) of copper or nickel into La-doped ceria, Ce(La)Ox, had a markedly different effect on the catalyst selectivity under fuel-rich conditions. The Cu–Ce(La)Ox catalyst has higher selectivity to elemental sulfur and complete oxidation products (H 2O, CO 2), while Ni–Ce(La)Ox favors the formation of H 2S and partial oxidation products (CO). The catalyst activity/selectivity studies were complemented by SO 2 uptake experiments and by reduction of the as-prepared and pre-sulfated catalysts in methane, both isothermally and in the TPR mode. The initial rate of reduction of pre-sulfated catalysts with methane is similar for Ce(La)Ox, Cu–Ce(La)Ox and Ni–Ce(La)Ox in the temperature range of 500-700°C. Activation of methane on these surfaces requires partial sulfate decomposition.