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.

Promoting effect of Fe/La loading on γ-Al2O3 catalyst for hydrolysis of carbonyl sulfur

Catalytic hydrolysis of carbonyl sulfur (COS) from blast furnace gas is one of the keys to achieving ultra-low emission in the iron-steel industry. To improve the COS hydrolysis activity on γ-Al₂O₃ catalyst at low temperature, catalysts with Fe or La as the active component were prepared by the impregnation method, the physical and chemical properties of the catalyst were characterized by ICP, XRF, XRD, BET, and TPD. The hydrolysis activity of COS and sulfur resistance ability on various catalysts were investigated in a fixed bed reactor combined with gas chromatography. The results show that the addition of Fe or La improves the COS hydrolysis activity due to the increase in alkaline sites on the catalyst surface. The roles of various alkaline sites on catalysts have been recognized. The weak alkaline center is the reaction site of COS hydrolysis, the middle and strong alkaline centers are the adsorption and oxidation sites of H₂S. The Fe/Al₂O₃ catalyst has higher hydrolytic activity and oxidative capacity for H₂S removal due to forming more sulfate species on Fe. The La/Al₂O₃ catalyst has higher hydrolysis efficiency in that H₂S rapidly desorbs from the catalyst surface to the gas phase, and then, the activity of reaction sites is recovered. This provides an idea for the preparation of sulfur-resistant catalysts.

Nickel Sulfides Decorated SiC Foam for the Low Temperature Conversion of H₂S into Elemental Sulfur

The selective oxidation of H₂S to elemental sulfur was carried out on a NiS₂/SiC^foam catalyst under reaction temperatures between 40 and 80 °C using highly H₂S enriched effluents (from 0.5 to 1 vol.%). The amphiphilic properties of SiC foam provide an ideal support for the anchoring and growth of a NiS₂ active phase. The NiS₂/SiC composite was employed for the desulfurization of highly H₂S-rich effluents under discontinuous mode with almost complete H₂S conversion (nearly 100% for 0.5 and 1 vol.% of H₂S) and sulfur selectivity (from 99.6 to 96.0% at 40 and 80 °C, respectively), together with an unprecedented sulfur-storage capacity. Solid sulfur was produced in large aggregates at the outer catalyst surface and relatively high H₂S conversion was maintained until sulfur deposits reached 140 wt.% of the starting catalyst weight. Notably, the spent NiS₂/SiC^foam catalyst fully recovered its pristine performance (H₂S conversion, selectivity and sulfur-storage capacity) upon regeneration at 320 °C under He, and thus, it is destined to become a benchmark desulfurization system for operating in discontinuous mode.

Hydrogen sulfide oxidation in novel Horizontal-Flow Biofilm Reactors dominated by an Acidithiobacillus and a Thiobacillus species

Hydrogen Sulfide (H2S) is an odourous, highly toxic gas commonly encountered in various commercial and municipal sectors. Three novel, laboratory-scale, Horizontal-Flow Biofilm Reactors (HFBRs) were tested for the removal of H2S gas from air streams over a 178-day trial at 10°C. Removal rates of up to 15.1 g [H2S] m(-3) h(-1) were achieved, demonstrating the HFBRs as a feasible technology for the treatment of H2S-contaminated airstreams at low temperatures. Bio-oxidation of H2S in the reactors led to the production of H(+) and sulfate (SO(2-)4) ions, resulting in the acidification of the liquid phase. Reduced removal efficiency was observed at loading rates of 15.1 g [H2S] m(-3) h(-1). NaHCO3 addition to the liquid nutrient feed (synthetic wastewater (SWW)) resulted in improved H2S removal. Bacterial diversity, which was investigated by sequencing and fingerprinting 16S rRNA genes, was low, likely due to the harsh conditions prevailing in the systems. The HFBRs were dominated by two species from the genus Acidithiobacillus and Thiobacillus. Nonetheless, there were significant differences in microbial community structure between distinct HFBR zones due to the influence of alkalinity, pH and SO4 concentrations. Despite the low temperature, this study indicates HFBRs have an excellent potential to biologically treat H2S-contaminated airstreams.