Catalytic biomass gasification has received extensive attention from scholars worldwide. This study proposes steam gasification of corn stover using red mud (RM), an industrial solid waste, as a catalyst to produce high-quality reducing gas. Experiments were conducted at different reaction temperatures and gasification times. Characterization of RM and its three main components, Fe2O3, CaCO3, and Al2O3, in the catalytic steam gasi-fication process of corn stover, was performed and its catalytic mechanism was explored by characterizing magnetic separation products. Results show that an increase in reaction temperature significantly promotes the production of CO, CO2, and H2. The promotion of steam to H2 production is caused by the gas-phase reaction and gasification of fixed carbon (FC). Fe2O3 promotes gas-phase reactions, such as the water-gas shift reaction, and effectively catalyzes the steam gasification of FC as an intermediate reactant. The addition of Al2O3 is beneficial for the production of CH4 and H2. The CO2 produced by the decomposition of CaCO3 inhibits the water-gas shift and methane-steam reforming reactions, thus reducing H2 output. The addition of RM is beneficial for the production of H2 and CO2 and inhibits the production of CO. Compared with pure Fe2O3, the superior pore structure and unique solid solution structure of RM provide Fe2O3 with more active surface lattice oxygen, higher redox performance, larger gas-solid contact area, superior ability to prevent carbon deposition, and better catalytic ability.

With catalytic pyrolysis gradually becoming the most efficient thermal treatment for biomass, the search for catalysts with high economic and catalytic performances has attracted widespread attention from scholars. In this study, the use of red mud as a catalyst for the pyrolysis of biomass to produce high-quality pyrolysis gas was investigated. The effects of the three components of red mud (Fe2O3, Al2O3, and CaCO3) on pyrolysis and the catalytic effect and mechanism of red mud on pyrolysis were analyzed. Fe2O3 was the most dominant catalyt-ically active ingredient in red mud, which had a good contribution to the improvement of carbon conversion and hydrogen yield. Specifically, Fe2O3-catalyzed corn stover pyrolysis at a 40 % addition ratio increased the hydrogen yield by 82 %. Because of the stable pore structure provided by Al2O3 and SiO2 as carriers and the chimeric structure of the catalyst particles, the specific surface area of the red mud reached 25.88 m2/g, and the specific surface area of the magnetic separation product reached 42.41 m2/g, which greatly improved the cat-alytic performance. Red-mud-catalyzed corn stover pyrolysis with a red mud addition ratio of 40 wt% could achieve an H2 yield of 108 ml/g, representing a rise of 79 %. The phase composition and crystal structure of the red mud and magnetic separation products were analyzed; the components in the red-mud catalyst doped with each other at the lattice level in the form of a solid solution, which improved the catalytic activity.

With the increase in global energy consumption, it has become difficult for traditional energy (re)sources to meet our basic needs. Hydrogen energy is an important component of a low-carbon or carbon-free energy strategy, and the thermochemical sulfur-iodine cycle is considered to be one of the most promising methods for hydrogen production. Nitrogen-doped activated carbon catalysts (NACCs) can improve the decomposition efficiency of hydrogen iodide (HI). However, the investigation of the active nitrogen-containing functional group (NFG) is still in progress. In this study, results from experiments and density functional theory (DFT) calculations were combined to achieve a pyridine nitrogen targeted modification, with the idea that pyridine nitrogen is the catalytically active center. Using ammonia-carbon dioxide co-activation, the samples contained a maximum of 7.79 % N content, and 77.28 % pyridine nitrogen content. An increase in the pyridine nitrogen content resulted in an increase in the catalytic decomposition efficiency. Bipyridine was used to increase the pyridine nitrogen content to complement the nitrogen-modulation mechanism. The N-6 content reached a maximum when the bipyridine solution con-centration was in the range of 0.3-0.35 g/L; this resulted in the highest catalytic efficiency. The transition state and reaction path energies were calculated at the B3LYP/def2-TZVP level and combined with thermodynamic enthalpy correction quantities to improve accuracy. According to the DFT calculations, the models for pyridine nitrogen substitution all reduced the activation energy of HI decomposition reaction compared to the other models.

As treatments for mainstream pollutants in coal-fired power plants have been established, the control of non-conventional pollutants, such as SO3 and HCl, is gradually gaining attention. In this study, combined SO3 and HCl removal is proposed based on SO3 removal by absorber injection. However, it is challenging to selectively absorb SO3 and HCl from SO2-rich atmospheres. Therefore, Ca(OH)2 was modified via ball milling and doping with CuO for the combined removal of SO3 and HCl. The results showed that ball milling reduced the particle and grain sizes of Ca(OH)2, which increased the active sites of Ca(OH)2 and prolonged reaction time. After modification by ball milling, SO3 absorption per mg of Ca(OH)2 increased by 40 %. However, HCl removal efficiency was difficult to improve by modifying Ca(OH)2 using only ball milling under SO3 and SO2 atmospheres. Therefore, the dechlorination capacity of Ca(OH)2 was improved by adding ions during the ball milling process. Doping of Ca(OH)2 with Cu2+ changed its crystal structure, weakened the diffusion resistance of HCl, and improved Ca(OH)2 utilization. Additionally, it increased the energy of Ca(OH)2 to adsorb HCl.

CaSO4 reduction decomposition for CaO preparation provides a theoretical basis for the utilization of the in-dustrial byproduct, gypsum. In this study, the effects of temperature (950 degrees C-1150 degrees C), CO2/CO partial-pressure ratio (1-15), CO concentration (1%-5%), and O-2 concentration (1%-7%) on the preparation of CaO from CaSO4 by CO reduction decomposition under different reaction atmospheres were investigated. The physical properties of CaO prepared by the decomposition of CaSO4 and CaCO3 were analyzed and compared. Finally, the reaction mechanism of the reduction decomposition of CaSO4 to CaO by CO was studied. The findings reveal that CaSO4 can be completely decomposed into CaO when the reaction temperature exceeds 1000 degrees C, CO% >= 2%, and P (CO2)/P(CO) >= 8. Furthermore, the addition of an appropriate amount of O-2 can improve the yield of CaO in the products. In an O-2-CO-N-2 atmosphere, where O-2% = 7% and CO% = 16%, CaSO4 can be completely decom-posed into CaO without the addition of CO2. The physical properties of CaO prepared by the reduction and decomposition of CaSO4 are better than those prepared by the calcination of CaCO3. An analysis of the reaction mechanism of the reduction decomposition of CaSO4 by CO reveals that CaSO4 generates CaO and CaS simul-taneously. In addition, CaS can react with unreacted CaSO4 to form CaO. Furthermore, it can react with CO2 to produce CaO if an appropriate amount of CO2 is added to the reaction atmosphere. The secondary interactions of CaS with CaSO4 and CO2 can significantly improve the yield of CaO in the product.

Denitration (De-NOx) over activated cokes (ACs) for sintering flue gas needs intensification. Gaseous reactions in a gas mixture containing NO, NO2, and NH3, with the effect of O2 concentration and moisture, were taken into consideration in the study of NOx conversion over ACs. Experimental studies on NOx conversion with and without NH3 over ACs were conducted using a fixed-bed reactor at 100 °C. The results demonstrated that moisture significantly affected NOx removal over ACs, especially the NO2 conversion. Under dry conditions, a disproportionation reaction of NO2 over ACs dominated NOx conversion with no NH3, whereas apparent fast selective catalytic reduction (SCR) over the ACs was observed in the presence of NH3. Regardless of the presence of absence of NH3 in wet mixtures, NO2 adsorption on ACs via the disproportionation route dominated the NOx conversion. Increasing the NO2/NO ratio in the simulated flue gas enhanced the NOx conversion rate over ACs. −C(ONO2) deposition on ACs generated by the disproportionation route inhibited NOx conversion with time. O3 oxidation was found to be efficient in increasing the NO2/NO ratio and intensifying the NOx conversion compared with commercially direct NH3-SCR over ACs. Increasing the temperature and decreasing the gas hourly space velocity can promote NOx conversion over ACs after O3 oxidation. NO oxidized with O3 coupled with NH3 spray and continuous regeneration of ACs is a potential method for removing NOx from sintering flue gas.

To solve the problems of difficult treatment of desulfurized gypsum and overmining of limestone, a kind of lime/gypsum flue gas desulfurization (FGD) collaborative desulfurized gypsum resource utilization process (LCS) was proposed. The system mainly includes the LCS-LFGD (lime/gypsum flue gas desulfurization system), LCS-C (desulfurized gypsum reduction calcining process), and carbon monoxide-coupled activated carbon reduction of SO2 to sulfur process (LCS-S). Taking a typical wet FGD unit of 300 MW power plant in China as an example, the limestone/gypsum flue gas desulfurization system (L-FGD) process was compared with the LCS by using the method of life cycle assessment and life cycle cost (LCC). The result shows that the overall environmental impact of the LCS is 0.2913. The environmental impacts of LCS-LFGD, LCS-C, and LCS-S were 0.1322, 0.1543, and 0.0048, respectively. Both LCS-LFGD and LCS-C are the key processes in this case study, and electricity consumption and coal gas consumption are the key substances in each key process. LCC analysis showed that although the initial investment of LCS was 4.32 x 10(6) USD similar to 5.76 x 10(6) USD more compared with L-FGD, the running cost of LCS was 1.41 x 10(6) USD per year lower compared with L-FGD. Besides, the cost of ore mining, the quality of calcined products, and environmental protection policy will affect the financial cost of the process.

To develop a new process of sulfur recovery for activated coke desulfurization, reduction of sulfur dioxide by activated coke and pyrolysis gas from powder coke fast preparation system was studied experimentally and theoretically. The distribution of gas products in the experiment was measured by GC-MS analyzer and refinery gas analyzer, while the thermodynamic equilibrium data was calculated by the Factsage software. The activated coke presented great catalytic performance for SO2 reduction by CO and H2. The reactivity of CO reducing SO2 was higher than that of H2, and the two gaseous reducing agents were independent of each other during the reaction process. The effect of CO2 on SO2 reduction was slight, while the participation of H2O resulted in a significant decrease in S yield. The unsteady state experiment shows that the catalytic ability of activated coke did not affect by reaction between carbon and SO2, CO2 or H2O.

To develop a new process for reducing SO2 to elemental sulfur, the reduction of SO2 with carbon materials heated by electrical and microwave were investigated on a fixed bed experimental system. The effects of carbon species, temperature, SO2 concentration and C/SO2 molar ratio on SO2 reduction were studied. The results showed that coconut shell activated carbon has the best reduction effect among the six carbon materials. With the increase of reaction temperature, the XSO2 gradually increased. However, the YS rapidly decreased at 800°C and reached a minimum value of only 55 % at 900℃. The XSO2 increased with the increase of C/S mole ratio, but the YS showed a different trend according to the different reaction temperature. By comparing the effects of microwave heating and electrical heating on the reduction of SO2, the much lower temperature was required to obtain the same XSO2 under microwave heating than that under electrical heating. Also for the SS, the results obtained under microwave heating were higher than that of electrical heating. When the reaction temperature was 950℃, XSO2 was about 98 % under both heating modes. However, YS under microwave heating was 95 %, while YS under electrical heating was only 85 %.

To develop a new method to recover elemental sulfur from the desulfurization process, a study on the sulfur evolution mechanism during the reduction of SO2 with CO over carbon was carried out. Thermodynamic equilibrium calculations showed that the elemental sulfur, as well as CO2, is the primary product of SO2 reduction with a CO/SO2 ratio of 2. Carbonyl sulfide (COS), instead of elemental sulfur, became the primary S-containing product with a CO/SO2 ratio of 3. Moreover, it decomposed to CO and elemental sulfur at temperatures above 500 degrees C. Experimental results showed that during the CO-SO2 reaction over carbon materials, COS was formed as a byproduct in the gaseous phase and elemental sulfur was generated following a COS intermediate mechanism. In the solid phase, SO2 reacted with the carbon surface to form oxidized S-containing compounds and these compounds were reduced by CO. COS did not reduce the oxidized S-containing compounds but combined with the carbon matrix to form reductive compounds. The abundant pore structure of the carbon surface was beneficial for SO2 reduction, as it enhanced the generation of oxidized S-containing compounds. Moreover, high Fe2O3 content improved the reactivity due to the formation of metallic sulfides.

Experiments and thermodynamic equilibrium calculations were carried out on a H2-SO2 system. The effects of temperature, H2/SO2 ratio, and retention time on SO2 reduction in an activated carbon bed were studied. The equilibrium calculations showed elemental sulfur to be the major S-containing product of SO2 reduction at low H2/SO2 ratios. However, when the H2/SO2 ratio was greater than three, the calculations predicted that SO2 would be completely reduced to H2S with elemental sulfur completely absent from the reduction products. The experimental results showed that the starting temperature for reduction of SO2 with H2 is 600 °C. In the presence of activated carbon, the starting temperature decreased and an obvious increase in the SO2 conversion and S yield was achieved at temperatures below 800 °C. The experimental results showed a lower SO2 conversion and higher S selectivity than those predicted by the equilibrium calculations because equilibrium was not achieved under the experimental conditions. Higher H2/SO2 ratios and longer retention times were beneficial to SO2 conversion. They also improved the S yield initially; however, subsequently, the yield decreased because an increase in S-containing byproduct formation after complete SO2 conversion was achieved. The activity of mixed H2/CO gas for SO2 reduction was also probed. CO displayed a higher SO2 reduction activity in comparison with H2. COS was the major S-containing byproduct at lower temperatures, while H2S was the main byproduct at 800 °C. At a H2/CO ratio of 1, the optimum SO2 conversion and S yield achieved were 99.3% and 79.3%, respectively, at 700 °C with a (H2 + CO)/SO2 ratio of 2.5.

To develop a new process for reducing high-concentration SO2 to elemental sulfur, the reduction of SO2 with CO and activated carbon in a fixed bed experimental system was investigated. The effects of temperature, CO/SO2 molar ratio, and reaction time on SO2 reduction were studied. The results showed that the starting temperature of SO2 reduction with activated carbon was approximately 700 degrees C and that the addition of CO decreased the starting temperature to 400 degrees C. Higher temperature led to an increase in SO2 conversion. The S yield also increased initially but then decreased when the temperature exceeded 800 degrees C, due to the formation of COS. SO2 conversion increased with an increasing CO/SO2 molar ratio, the optimum S yield being achieved at a CO/SO2 ratio of 2. However, the existence of unreacted SO2 in the product decreased the S yield and resulted in an optimum S yield occurring at a low ratio. Lower selectivity of SO2 reduction to elemental sulfur was observed if reaction time was reduced. By prolonging gas-carbon contact time, the S yield increased and gradually approached SO2 conversion at temperatures below 700 degrees C. The catalytic mechanism over activated carbon conformed to the COS intermediate mechanism, and the rate of the overall CO-SO2 reaction was determined by the Claus reaction between COS and SO2.