Boudouard Reaction Research Articles

Effect of pyrolysis parameters on the biochar reactivity in the N-absorption reaction of chemical looping ammonia generation

Biochar from slow pyrolysis was applied to Chemical Looping Ammonia Generation (CLAG) to avoid the preparation of ammonia from fossil fuels and relatively expensive H2. The effects of pyrolysis atmosphere, temperature, heating rate, and residence time on the biochar reactivity in the N-adsorption reaction were investigated. The relationship between specific surface area, average pore diameter, micropore percentage, and disorder degree of biochar on reactivity was evaluated by simple and multiple linear regression and Analysis of Variance (ANOVA). The results showed that the biochar prepared in a CO2 atmosphere with a pyrolysis temperature of 700 °C, a heating rate of 10 °C/min, and a resident time of 30 min had the highest conversion rate of 57.79 % in the N-absorption reaction. When the pyrolysis temperature was increased from 600 °C to 700 °C, the biochar conversion in the N-adsorption reaction was significantly increased due to the Boudouard reaction during biomass pyrolysis. The linear regression and ANOVA results show that the micropore percentage and disorder degree of biochar significantly positively affected the reactivity, guiding feedstock selection and optimization of the preparation method of the carbon source used for CLAG.

Effect of nickle on cerium oxide support to develop cyclic catalytic methane decomposition followed by CO2 gasification

Catalytic methane decomposition (CMD) offers an eco-friendly method to produce COx-free hydrogen and solid carbon. An innovative approach for catalyst regeneration involves utilizing CO2 as a reactant to produce CO via the Reverse Boudouard Reaction, which serves as a valuable feedstock for various chemicals and fuels. This study aims to investigate the role and interaction of Ni nanoparticles on cerium oxide support by comparing two catalysts: one synthesized via the conventional impregnation method (Imp) and the other through solution combustion synthesis (SCS). Both catalysts containing the same Ni loading of 5 wt% and were tested under identical conditions. Comprehensive characterization techniques, including XRD, H2 and O2 TPR, TEM, SEM, XPS, and Raman spectroscopy, were employed to elucidate the observed performances. The SCS catalyst resulted in smaller Ni nanoparticles with stronger metal-support interaction. Observations revealed both tip and base carbon growth for the SCS catalyst, whereas the Imp catalyst predominantly characterized by tip growth. For the SCS catalyst, carbon nanofibers and nanotubes were observed, and both appeared active in carbon CO2 gasification. For the Imp catalyst, more crystalline carbon is observed. The amount of carbon produced was much more and managed to cover the entire catalyst. For SCS carbon coverage was partial. Two rates of CO2 gasification were observed depending on the extent of carbon coverage. Across all tested temperatures and space velocities, the catalyst prepared by impregnation exhibited higher reaction rates. The Imp catalyst demonstrated 15 % higher CMD and 29 % more generated carbon than SCS. This work demonstrated the critical role of key factors influencing the catalytic performance of this cyclic process. This includes the Ni nanoparticle size and distribution, the metal-support interaction's strength, and the graphitic carbon's nature.

Ga-doped spinel-typed Co-Al catalysts for CO2-assisted ethane dehydrogenation

A series of Ga-doped spinel-typed Co-Al catalysts were prepared via one-step evaporation-induced self-assembly (EISA) method. These catalysts present promising catalytic performance for CO2-assisted ethane dehydrogenation, which can be ascribed to the conjunction effect of cobalt and gallium species. The incorporation of Ga into the structure of Co-Al spinel has been recognized for enhancing CO2 conversion via reverse water-gas shift reaction, leading to a favorable equilibrium shift towards ethylene, along with an improved catalyst stability as a result of coexisting Boudouard reaction. Through X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), NH3 and CO2 temperature-programmed desorption (TPD) characterizations, coordinatively unsaturated Co2+ and Ga3+ cations were identified as collaborative catalytic active sites, with gallium species taking the prominent role. These sites were closely associated with the formation of acid-base pairs on the catalyst surface, which were crucial for the adsorption and activation of the reactants.

Reforming of methane over two-dimensional Mo2C-Ni/γ-Al2O3 catalyst

The impact of two-dimensional Mo2C (2D-Mo2C) on the activity and stability of a Ni/γ-Al2O3 catalyst for the dry reforming of methane (DRM) is reported. 1.1 wt% 2D-Mo2C added to 13 wt% Ni/γ-Al2O3 increased activity by ∼40 %. Characterization results showed an interaction between 2D-Mo2C and Ni that resulted in the formation of a NixMoy bulk phase (XRD) and Ni-Mo-oxycarbide surface species (XPS). The presence of 2D-Mo2C also improved the stability of the catalyst compared to Ni/γ-Al2O3 by reducing coke deposition. H2 space-time-yields (STYs) were independent of CO2 partial pressure and were lower than the CO STYs. Power law kinetic models were consistent with a DRM reaction pathway via CH4 decomposition (MD) and the reverse Boudouard (RBD) reactions.

Numerical Modeling of Electrolyte-Supported Button Solid Oxide Direct Carbon Fuel Cell Based on Boudouard Reaction

Numerical Modeling of Electrolyte-Supported Button Solid Oxide Direct Carbon Fuel Cell Based on Boudouard Reaction

Calcium looping-enhanced biomass gasification for methanol production: Integrating methane dry reforming and carbon utilization

Developing integrated CO2 capture and utilization (ICCU) is an attractive strategy that aims to reduce CO2 emissions while realizing the potential benefits of CO2. This paper investigates the techno-environmental-economic performance of biomass gasification to methanol (BtM) based on calcium looping (CaL) coupled with dry reforming of methane (DRM) and CaL coupled with reverse Boudouard reaction (RB). The results indicate that BtM systems based on CaL-DRM (BtM:CaL-DRM) and CaL-RB (BtM:CaL-RB) achieve CO2 capture and utilization, and enable efficient methanol synthesis. Compared to BtM:CaL-DRM, BtM:CaL-RB demonstrates higher exergy efficiency and lower global warming potential (GWP). The exergy efficiency of BtM:CaL-RB reaches 71.60 %. In terms of economic viability, BtM:CaL-DRM demonstrates more promising economic feasibility. The BtM systems reaches breakeven when the methanol selling price ranges from 440.8 $/ton to 529 $/ton. This study provides valuable insights into exploring novel ICCU systems.

Enhancement of non-thermal plasma-catalytic CO2 reforming of CH4 using Ni/Mg–Al2O3 catalysts in a parallel plate dielectric barrier discharge reactor

CO2 and CH4 are converted to syngas by dry reforming of methane (DRM) reaction. This research investigated the effects of the Mg promoter on Al2O3-supported Ni catalysts and Mg calcination temperature on the DRM performance in a parallel plate dielectric barrier discharge reactor. The Mg promoter played a crucial role in the DRM performance, as increasing the Mg calcination temperature from 700 °C to 800 °C significantly improved the DRM performance and catalyst properties, including increased specific surface area, decreased total acidity, reduced crystallite and particle sizes, and more uniform dispersion of the Ni nanoparticles. Under these conditions, the H2 and CO selectivity were 77.0 % and 70.7 %, the CH4 and CO2 conversion were 25.1 % and 20.6 %, and the energy efficiency was 8.4 %. In addition, the catalyst was associated with a lower coking rate (0.5 mg C/gcat h), a relatively low carbon deposit of 1.5 %, and a carbon loss of 2.8 %, possibly because the weak acidity hindered the Boudouard reaction and CH4 decomposition. However, increasing the Mg calcination temperature to 900 °C increased the total acidity and Ni particle size, decreasing H2 and CO selectivities and increasing carbon deposits on the catalyst surface.

Modeling of Fluidized Bed Molten Carbonate Direct Carbon Fuel Cell: Effect of Reverse Boudouard Reaction

Direct carbon fuel cells (DCFCs) are an alternative technology to coal-fired power plants for converting the chemical energy of abundant carbon-rich fuel into electrical energy. DCFCs have higher electrical efficiency and lower greenhouse emissions, which are easier to separate and capture. In the transition to renewable sources of energy, efficient and low-emission technologies need to be explored. Since DCFC technologies are in their early stages of development, modeling and simulation studies are needed to reduce costs and aid in experimental design. In this study, an electrochemical and transport model for a fluidized bed molten carbonate DCFC (FBMCDCFC) is developed. The performance of the fuel cell is evaluated through the polarization losses. This study expounds on recent developments in DCFCs by considering the effect of the reverse Boudouard reaction and the 2-electron oxidation of CO alongside the 4-electron oxidation of carbon at higher temperatures. The electrolyte used is a 62 : 38 mol % Li2CO3/K2CO3 eutectic mixture, while the fuel is activated carbon impregnated by HNO3. The results show that the greatest polarization losses for the FBMCDCFC are from anode activation overpotential and ohmic overpotential. The cathode activation and concentration overpotentials are relatively small. Increasing the reaction temperature results in a greater decrease in anode activation overpotential than ohmic overpotential, despite the increase in CO formation from the reverse Boudouard reaction. The peak power density of the FBMCDCFC is 434.437 W m-2 when operated at 923 K and a gas flow rate of 30 mL min-1. The peak power density of the FBMCDCFC is greater with higher temperatures, where the peak increases to 584.802 W m-2 when operated at 1023 K. The peak power density is greater with lower gas flow rates, where the peak increases to 458.175 W m-2 at a gas flow rate of 25 mL min-1. The mathematical model can aid in optimizing the performance of FBMCDCFCs, such as how increasing the operating temperature favorably increases anode reaction kinetics and reduces ohmic resistances in the cell. Future work will focus on improving the model correlations to close the gap between the results of modeling and actual experiments.Figure 1. a) Power curves at different temperatures, 823 K to 1323 K (30 mL min-1 flow rate, 1 atm total pressure); b) Power curves at different gas (O2 and CO2) flow rates (923 K, 1 atm total pressure) Figure 1

A comprehensive thermodynamic analysis of hydrogen and synthesis gas production from steam reforming of propionic acid: Effect of O2 addition and CaO as CO2 sorbent

A thermodynamic analysis was performed for the production of synthesis gas and hydrogen gas from steam reforming of propionic acid, one of the constituents of the bio-oil, using ASPEN Plus v8.8. The aim of the study was to perform a global analysis on steam reforming of propionic acid focusing on several parameters such as steam-to-propionic acid ratio, reaction temperature, addition of O2 in the feed stream and presence of CaO as a CO2 sorbent in the reaction environment. The results showed that higher amounts of steam/propionic acid ratio resulted in higher H2 and CO2 yields. It was also observed that high H2O/PA molar ratios led to reduced coke production as WGS reaction was favored with excess steam, causing CO in the reaction mixture to be consumed through the WGS reaction rather than the Boudouard reaction. Addition of O2 in the reaction environment was observed to negatively affect yield of H2. Yet, coke formation was deprived and increasing the O2 amount in the feed stream decreased the energy required for the process. Furthermore, the presence of CaO enhanced H2 yield and energy requirements of the process compared to conventional steam reforming process. 100 % yield of H2 production with a heat generation of −83.4 MJ/kmol of PA and almost zero formation of CO2, CO, CH4 and coke is achieved at 600 °C for sorption enhanced steam reforming of propionic acid.

Investigating the Effects of the Physicochemical Properties of Cellulose-Derived Biocarbon on Direct Carbon Solid Oxide Fuel Cell Performance.

This paper presents a study of the characteristic effects of the physicochemical properties of microcrystalline cellulose and a series of biocarbon samples produced from this raw material through thermal conversion at temperatures ranging from 200 °C to 850 °C. Structural studies revealed that the biocarbon samples produced from cellulose had a relatively low degree of graphitization of the carbon and an isometric shape of the carbon particles. Based on thermal investigations using the differential thermal analysis/differential scanning calorimeter method, obtaining fully formed biocarbon samples from cellulose feedstock was possible at about 400 °C. The highest direct carbon solid oxide fuel cell (DC-SOFC) performance was found for biochar samples obtained via thermal treatment at 400-600 °C. The pyrolytic gases from cellulose decomposition had a considerable impact on the achieved current density and power density of the DC-SOFCs supplied by pure cellulose samples or biochars derived from cellulose feedstock at a lower temperature range of 200-400 °C. For the DC-SOFCs supplied by biochars synthesised at higher temperatures of 600-850 °C, the "shuttle delivery mechanism" had a substantial effect. The impact of the carbon oxide concentration in the anode or carbon bed was important for the performance of the DC-SOFCs. Carbon oxide oxidised at the anode to form carbon dioxide, which interacted with the carbon bed to form more carbon oxide. The application of biochar obtained from cellulose alone without an additional catalyst led to moderate electrochemical power output from the DC-SOFCs. The results show that catalysts for the reverse Boudouard reactions occurring in a biocarbon bed are critical to ensuring high performance and stable operation under electrical load, which is crucial for DC-SOFC development.

Energy and exergy analysis of dry and steam external reformers for a power cycle based on biogas-fueled solid oxide fuel cell

In the present research a cogeneration cycle based on a solid oxide fuel cell (SOFC), and Organic Rankine Cycle (ORC) is proposed. The cycle is fed with biogas in different molar ratios of carbon dioxide to methane (RCTC). In addition, the cycle is examined for both dry reforming (DR) and steam reforming (SR). A thermochemical model is presented for both cycles of SR–SOFC–ORC, and DR–SOFC–ORC. The model is coded in MATLAB coupled with Engineering Equation Solver software. The model was verified with both experimental and theoretical research and agreement was achieved. The energy and exergy performance of the cycle is presented and carbon deposition on the cathode due to different reactions of methane cracking, Boudouard reaction, and vapor formation are studied. The results show that for RCTC<1.2 steam reforming produces more hydrogen, while for RCTC>1.2 dry reforming is advantageous. At RCTC = 1.2 the DR and SR work the same. The overall thermal efficiency of DR-SOFC and SR-SOFC has reached 67 % and 70 %. Carbon deposition due to the Boudouard reaction, and vapor formation for both SR and DR are negligible while due to methane cracking is serious. The DR-SOFC deposits less carbon because of methane cracking due to higher operating temperatures.

Localized thermal levering events drive spontaneous kinetic oscillations during CO oxidation on Rh/Al2O3

Unravelling kinetic oscillations, which arise spontaneously during catalysis, has been a challenge for decades but is important not only to understand these complex phenomena but also to achieve increased activity. Here we show, through temporally and spatially resolved operando analysis, that CO oxidation over Rh/Al2O3 involves a series of thermal levering events—CO oxidation, Boudouard reaction and carbon combustion—that drive oscillatory CO2 formation. This catalytic sequence relies on harnessing localized temperature episodes at the nanoparticle level as an efficient means to drive reactions in situations in which the macroscopic conditions are unfavourable for catalysis. This insight provides a new basis for coupling thermal events at the nanoscale for efficient harvesting of energy and enhanced catalyst technologies.

Experimental Study on the Improvement of Char Physicochemical Properties and Reactivity by Activation Process in CFB.

Solid carbon can be transformed into activated char with higher reactivity through the activation process in a circulating fluidized bed (CFB) to improve the Boudouard reaction. A new technology for reducing CO2, the activated-reduction technology, was proposed. In order to investigate the influence of relevant parameters (carbon dioxide addition, oxygen concentration, and O2/C) of the activation process on the physicochemical properties and reactivity of activated char, the experiments were carried out on a bench-scale CFB. The relationship between the parameters and the reactivity of activated char is explored. The result shows that compared with the raw coal, the pore structure of activated char is developed, the number of active sites increases, the degree of graphitization decreases, and higher reactivity is possessed. For the activation process, less of the O2/C and moderate oxygen concentration promote the increase in activated char reactivity, which is conducive to the reduction of CO2. The results of the correlation discussion show that the reactivity is difficult to be characterized by a single simple parameter. The reactive specific surface area (RSSA) obtained by multiplying the mesoporous specific surface area and I D3+D4/I all has a good effect on describing the reactivity.

The role of reverse Boudouard reaction during integrated CO2 capture and utilisation via dry reforming of methane

Integrated carbon capture and utilisation (ICCU) is an emerging technology for simultaneous CO2 adsorption and conversion into value-added products. This provides a more sustainable approach compared to carbon capture and storage. Dual-functional materials (DFMs) that couple CO2 sorbents (e.g. CaO) and catalysts (e.g. Ni) enable direct utilisation of sorbed CO2 for reactions like dry reforming of methane (DRM). However, the potential interactions between sorbent and catalyst components within DFMs may induce distinct mechanisms compared to individual materials. Elucidating these synergies and interfacial phenomena is vital for guiding the rational design of DFMs. This article investigates the respective roles of Ni/SiO2 catalyst and sol–gel synthesised CaO sorbent in integrated CO2 capture and utilisation via dry reforming of methane (ICCU-DRM) using a decoupling approach. Through decoupled reactor experiments, it is found that Ni/SiO2 activates CO2 to react with carbon deposits from CH4 decomposition, achieving maximal CO and H2 yields of 43.41 mmol g−1 and 46.78 mmol g−1 as well as 87.2 % CO2 conversion at 650 °C. Characterisation shows that coke would encapsulate Ni nanoparticles and be active for CO2 conversion via Boudouard reaction, indicating sufficient catalyst-sorbent contact is necessary for CO2 spillover. In-situ DRIFTS reveals that no obvious CH4-CaCO3 reaction occurs, CO2 chemisorption on Ni/SiO2 enables the reverse Boudouard reaction, which is further verified by DFT calculations. The findings elucidate the dependent and synergistic roles of Ni/SiO2 and CaO/CaCO3 in ICCU-DRM, and highlight the importance of catalyst-adsorbent interactions in optimising dual-functional materials.

High efficiency electricity and gas cogeneration through direct carbon solid oxide fuel cell with cotton stalk biochar

For the first time, biochar derived from a renewable resource, cotton stalk, is used as the feedstock of direct carbon solid oxides fuel cells (DC-SOFCs) for electricity and gas cogeneration. It turns out that the cotton stalk biochar has plenty of naturally grown K and Ca, which are active catalysts for the reverse Boudouard reaction in DC-SOFCs. This natural advantage of the cotton stalk biochar enables an extremely high power density of an anode-supported DC-SOFC at 850 °C, 0.9 W cm−2, which is the highest among those of the reported DC-SOFCs. Meanwhile, high concentration of CO gas, which is an important feedstock for chemical industry, is obtained from the DC-SOFCs. The energy conversion efficiency of the electricity-gas cogeneration of DC-SOFCs reaches over 70%. A novel method, using compressed char, is proposed and carried out for continuous supply of cotton stalk char to a DC-SOFC. The present work has demonstrated the feasibility and advantages of cogenerating electricity and gas through DC-SOFCs with biochar derived from cotton stalk as the feedstock.

Unraveling the intrinsic mechanism behind the retention of arsenic in the co-gasification of coal and sewage sludge: Focus on the role of Ca and Fe compounds

Minimizing the emission of arsenic (As) is one of the urgent problems during co-gasification of Shenmu coal (SM) and sewage sludge (SS). The intrinsic mechanism of As retention was obtained by analyzing the effect of different SM addition ratios on the As form transformation during co-gasification at 1000 °C under CO2 atmosphere. The results showed that the addition of SM effectively promoted the enrichment of As in the co-gasified residues. Especially, the best As retention rate of 65.71% was achieved with the 70 wt% addition ratio of SM. The addition of SM promoted the adsorption and chemical oxidation of As(III) to the less toxic As(V) through the coupling of Ca and Fe compounds in the co-gasified residues. XRD and XPS results indicated that Fe2O3 adsorbed As2O3(g) after partial conversion to Fe3O4 by the Boudouard reaction, while part of As2O3 was oxidized to As2O5 by lattice oxygen. Finally, the generated As2O5 was successively trapped by CaO and Fe2O3 to form stable Ca3(AsO4)2 and FeAsO4. HRTEM and TEM analysis comprehensively proved that As(III) was stabilized by the lattice cage of CaAl2Si2O8. In conclusion, the co-oxidation of Ca and Fe compounds and lattice stabilization simultaneously played a crucial role in the retention of As2O3(g) during co-gasification.

Chemical looping-based catalytic CH4 decomposition and successive coke gasification with CO2 on ordered mesoporous NiMCeOx (M = Co, Zr, La)

Highly ordered mesoporous NiLaCeOx mixed metal oxides were investigated as effective catalysts for the chemical looping-based dry reforming of methane (CH4) with carbon dioxide (CO2) (CL-DRM). This catalyst exhibited an excellent catalytic activity and stability in the decomposition of CH4 to form H2 with surface carbons subsequently activated by CO2 via reverse Boudouard reaction to form CO. Among the NiMCeOx catalysts with various promoter (M = Co, Zr, or La), the optimal NiLaCeOx catalyst preserved its original highly ordered mesoporous structures, leading to the higher dispersion of smaller Ni nanoparticles. This was attributed to the stronger Ni-Ce interactions facilitated by the La2O3 metal oxide promoter. The NiLaCeOx demonstrated a higher rate of H2 formation and successive CO production in the CL-DRM reaction, resulting in a H2/CO ratio above 1.0. Additionally, the NiLaCeOx catalyst exhibited superior structural stability over 5 cyclic CL-DRM reactions for CH4 decomposition (>85 %) and CO2 activation (>45 %), with minimal deposition of cokes.

Experimental study and equilibrium analysis on thermal reduction of CO2 by CFB gasification

CO2 can be involved in the CFB gasification process as one of the gasifying agents and be reduced to CO. In this paper, the feasibility of using CFB gasification process to reduce CO2 was investigated by using a bench-scale CFB gasifier. The effect of gasifying agent parameters including the CO2 substitution for N2, the O2 concentration and O2/C were studied. The result of experiments was compared with the chemical equilibrium calculations. The experimental result shows that the reduction of CO2 can be realized in CFB gasification, and the yield of CO in O2/CO2 atmosphere is higher than that in air atmosphere. When the O2 concentration is 30%, the CO2 conversion reached the maximum of 0.017 Nm3(CO2)/kg (coal). However, the conversion of CO2 is limited by temperature and char reactivity at higher CO2 concentration. The gradual increase in CO2 yield with increasing O2/C suggests that at approximate temperature, the increase in O2/C enhances the oxidation of C and CO. When O2/C is greater than 0.45, the gasification results reach equilibrium. Under other conditions, the gasification results differ from the chemical equilibrium significantly. This is due to the change in the dominant reaction of the gasification process from the combustion reactions to the Boudouard reaction.

Effect of Ni/SiO2 catalyst preparation method on methane decomposition and CO2 gasification cycles

Catalytic methane decomposition is a promising reaction to produce CO2-free hydrogen from methane-rich feedstock with solid carbon as a by-product. Significant research conducted on this reaction to find ways to manage and utilize this solid carbon. In this work, the methane decomposition reaction is followed by Reverse Boudouard Reaction using CO2 feedstock to convert the solid carbon to carbon monoxide, which is a valuable starting component for many chemical applications. Realizing this promising concept would require a catalyst that is efficient for both reactions. Herein, we explored the potential of using solution combustion synthesis (SCS) to make a 5 wt% of Ni supported SiO2 catalyst and benchmarked it versus the conventional impregnation method. The catalyst prepared by SCS showed an improved performance at different temperatures, space velocities, and catalyst pellet sizes. The SCS catalyst successfully completed five repeated cycles reaching up to 38.1 h of stable time on stream operation, whereas the impregnated catalyst was not able to complete the second testing cycle with only 14 h of time on stream operation. A thorough characterization using XRD, H2 and O2 TPR, TEM, SEM, XPS, and Raman spectroscopy were conducted to provide an adequate explanation for the observed performances for both catalysts. The Ni nanoparticles size and distribution, the strength of the metal support interaction, and the nature of graphitic carbon were the key factors affecting the catalytic performance. Insights on how to make an optimal catalyst for this promising process is identified which is a step forward toward making separated H2 and CO streams from methane feedstock and CO2, respectively.

Novel technology for synergistic SO2 reduction during the carbonation process via a CaO-Char mixed system

A novel method to effectively achieve synergistic SO2 reduction during the carbonation process by the as-designed CaO-biochar system is developed. Coconut shells and calcined-limestone were used as biochar and calcium sources (denoted as CSC and LS), respectively. The introduced reductant creates the reduction condition making the Ca-based sulfation suppressed and the desulfurization prefers to undertake the reduction pathway during the simultaneous CO2/SO2 removal process. The competition of SO2 and CO2 for the calcium active sites is weakened, effectively alleviating the negative effect of SO2 presence on CO2 carbonation and generating valuable sulfur-product. With the mass ratio of LS and CSC is 3, the carbonation conversion of the LS-CSC(1:3) is 34% higher than that of the LS and the reduced-sulfur ratio of the system reaches about 85% indicating an effective CO2 capture synergistic SO2 reduction. The CO produced via the Boudouard reaction between CO2 and char is sufficient to play an important role in SO2 reduction, which effectively promotes the decarboxylation process in the reduction of SO2. It also facilitates the sulfur transfer from the reduced intermediate on the solid phase to the gas phase as a form of COS, promoting the reduction of SO2 through the Claus reaction.