Highly Dispersed FeAg-MCM41 Catalyst for Medium-Temperature Hydrogen Sulfide Oxidation in Coke Oven Gas

Highly efficient sulfur production in hydrogen sulfide conversion over Fe3O4 with {111} crystal facets: Unveiling the promotion of oxygen vacancies and basic sites

High-performance catalysts for the selective catalytic oxidation of hydrogen sulfide (H2S-SCO) are required to achieve the conversion of hazardous H2S into harmless and valuable sulfur for environmental protection and resource utilization. Herein, three different morphologies of Fe3O4 were synthesized and used for H2S-SCO. Octahedral Fe3O4 dominated by {111} crystal facets exhibited excellent performance for H2S-SCO with an H2S conversion of ∼ 100 % and a sulfur selectivity exceeding 94.5 % in stability tests at 150 °C over 60 h. The {111} crystal facets provided weakly to moderately basic sites to promote H2S adsorption and dissociation, as well as abundant oxygen vacancies (OVs) due to lower OV formation energies on this facet, which significantly enhanced the oxidation performance of the catalyst. By revealing the promotions of OVs and basic sites, the relationship between the {111} crystal facets of Fe3O4 and the performance in the H2S-SCO was clarified. This study provides new insights into the design of efficient and stable Fe-based catalysts for the conversion of hazardous H2S from blast furnace gas into valuable sulfur.

Nano-flower spherical NiFe LDH adsorbent for efficient removal of H2S in blast furnace gas

Removal of sulfur species from blast furnace gas is urgently needed due to the strict emission limits imposed on iron-steel industrial flue gas. Improving the sulfur capacity of H2S is a crucial challenge to reduce the operation cost. NiFe layered double hydroxide (LDH) adsorbents were synthesized using the hydrothermal method to strengthen the adsorption of H2S, achieving a high sulfur capacity of 133.6 mg/g at 50 °C. Characterization studies have revealed that the reaction pathway of H2S on the NiFe LDH surface involves adsorption, dissociation and oxidation. It has been clarified that the high sulfur capacity can be attributed to the abundant H2S dissociation sites and the excellent O2 activation sites. The dissociation sites of H2S encompass metal sites, -OH and CO32-. The interaction between O2 and the bridge site of asymmetric metal atoms significantly enhances the dissociation of O2. Strengthening the dissociation of H2S and O2 improves the sulfur capacity. The deactivation of adsorbents comes from the continuous consumption of oxygen species mainly composed of -OH and the deposition of sulfur species in the smaller mesopores ranging from 2 to 10 nm. This work provides useful insights into designing highly efficient iron-based adsorbents for the desulfurization of blast furnace gas.

Combination of FeII-O Species and Fe-O-Zr Bonds Empowers FeOx Nanoclusters Anchored on UiO-66 Robust H2S-Selective Catalytic Oxidation Performance

The low sulfur selectivity of Fe-based H2S-selective catalytic oxidation catalysts is still a problem, especially at a high O2 content. This is alleviated here through anchoring FeOx nanoclusters on UiO-66 via the formation of Fe-O-Zr bonds. The introduced FeOx species exist in the form of FeIII and FeII. Therein the FeIII-O species are the predominant active sites for H2S-oxidation. The formed Fe-O-Zr bonds strengthen the redox cycle of FeIII/FeII through promoting electron transfer from Fe to Zr. The FeII-O species can activate molecular oxygen to oxidize H2S into elemental S, which accelerates the formation rate of atomic S, hindering its further oxidation into SO2. The combination of these factors empowers the catalysts, enabling 100% H2S conversion and 98.2% sulfur yield. The catalyst also has satisfactory stability with the sulfur selectivity only decreasing from 98.2% to 91.3% after the reaction going on 50 h. The decreased sulfur selectivity might be caused by the deterioration of pores and the deposition of elemental S on the surface. The former hinders the diffusion of sulfur oligomers timely from pores to the gas phase, while the latter is suspected to capture electrons to promote its further reaction with molecular oxygen.

Waste to Wealth: Discarded Cigarette Butt-Derived Metal-Free N-Rich Carbon Catalysts for the Selective Catalytic Oxidation of Hydrogen Sulfide to Sulfur

The selective catalytic oxidation of toxic gas H2S to elemental sulfur (H2S-SCO) is a promising desulfurization process known for its dual benefits of recovering valuable sulfur resources and mitigating environmental pollution. Nevertheless, developing cost-effective and efficient catalysts for H2S-SCO remains a significant challenge. In this study, we synthesized a low-cost and metal-free nitrogen-rich carbon catalyst (NrCC) by copyrolyzing discarded cigarette butts (organic solid wastes that are difficult to degrade naturally) with urea for the continuous H2S-SCO process at a relatively low temperature. The NrCC exhibited exceptional catalytic performance, achieving complete H2S conversion to sulfur at 180 °C, and demonstrated excellent stability in humid (RH = 80%) and high CO2 concentration environments. The catalyst succeeded due to its developed pore structure (specific surface area as high as 2267.77 m2·g-1) and abundant pyridine-N sites. DFT calculations showed that the pyridine-N neighbor carbon sites were the active sites promoting H2S adsorption and dissociation. This study presents a novel "waste control by waste" strategy that integrates the utilization of organic solid waste resources with air pollution control measures, showcasing the potential for sustainable environmental solutions.

Iron-Based Catalysts Derived from Iron-Containing Sludge for Enhanced Catalytic Performance of H2S Selective Catalytic Oxidation

In this work, iron-containing sludge is used to prepare iron-based catalysts for efficient H2S selective catalytic oxidation. First, the effect of calcination temperatures on the catalytic activities of H2S selective oxidation is carried out and it can be found that S-500 calcined at 500 °C performs excellent catalytic activity. Then, the catalytic performance of the S-500 catalyst is further optimized using alkaline treatment with different concentrations of NaOH solution. The results indicate that S-500(2.0) treated with 2 M NaOH solution has the highest catalytic activity of H2S selective oxidation. Next, various characterization methods are used to analyze the structure and physical-chemical of the sludge-based catalysts. N2-Brunauer-Emmett-Teller (N2-BET) and X-ray photoelectron spectroscopy analyses show that the S-500(2.0) catalyst has the smallest average particle (11.17 nm), the biggest ratio of S ext/S micro(17.98) with bigger external specific surface area (49.09 m2·g-1), a higher proportion of Fe3+ species (50.88%), and surface adsorbed oxygen species (48.07%). Meanwhile, O2-TPD and CO2-TPD analysis indicates that the S-500(2.0) catalyst has a bigger value of the Oads/OTotal ratio (50.56%) and (CO2)(weak+moderate) /(CO2)Total ratio of (31.41%), indicating that there are much more oxygen vacancies and weak alkaline sites. As a result, the excellent catalytic performance of H2S selective oxidation can be attributed to its outstanding physical-chemical properties.

Cu/Biochar Bifunctional Catalytic Removal of COS and H2S:H2O Dissociation and CuO Anchoring Enhanced by Pyridine N

Economic and environmentally friendly strategies are needed to promote the bifunctional catalytic removal of carbonyl sulfide (COS) by hydrolysis and hydrogen sulfide (H2S) by oxidation. N doping is considered to be an effective strategy, but the essential and intrinsic role of N dopants in catalysts is still not well understood. Herein, the conjugation of urea and biochar during Cu/biochar annealing produced pyridine N, which increased the combined COS/H2S capacity of the catalyst from 260.7 to 374.8 mg·g-1 and enhanced the turnover frequency of H2S from 2.50 × 10-4 to 5.35 × 10-4 s-1. The nucleophilic nature of pyridine N enhances the moderate basic sites of the catalyst, enabling the attack of protons and strong H2O dissociation. Moreover, pyridine N also forms cavity sites that anchor CuO, improving Cu dispersion and generating more reactive oxygen species. By providing original insight into the pyridine N-induced bifunctional catalytic removal of COS/H2S in a slightly oxygenated and humid atmosphere, this study offers valuable guidance for further C═S and C-S bond-breaking in the degradation of sulfur-containing pollutants.