Visible-Light Driven Gas Phase Hydrogen Sulfide Degeneration Using g-C3N4 Hybrid Photocatalysts and Its Countermeasures of Catalytic Poisoning
Authors: Katayama Tomofumi , Nagata Morio 
Published: December 2024

Hydrogen sulfide (H2S) is a toxic gas generated by chemical plants and geothermal power plants, with a rotten-egg bad odor. High concentration of H2S are lethal, and even concentrations as low as 2 ppm are known to cause adverse effects, such as nausea, eye tearing, and headaches. Also, continuous exposure to H2S causes diseases, for example nervous, sensory, and circulatory systems.
In Japan, the Offensive Odor Control Law standards for output concentration of H2S and such bad-odor gas is below 0.2 ppm. However, it is reported that 50% of humans can smell H2S at a concentration of 8 ppb, thus it is difficult to prevent an odor problem simply by complying with the legal regulations. The Claus method that is known as a treatment of H2S gas conversion with oxygen under high temperature and high pressure conditions to obtain molten sulfur requires a high H2S concentration (approximately 25%) in the feed and does not achieve complete removal, resulting in H2S emissions of approximately 100 ppm, which is unsuitable for fundamental odor control.
Photocatalytic environmental remediation is an effective technology currently under extensive investigation. There are several studies of gas-phase H2S decomposition using titanium dioxide (TiO2), however most of them involve decomposition as a sacrificial reagent after alkaline adsorption, or gas-phase decomposition under relatively high concentration conditions of 100 ppm or more. [1] Although hydrogen sulfide decomposition by TiO2 under low concentration conditions has been reported [2], hydrogen sulfide is decomposed by irradiation of UV light because TiO2 is not responsive to visible light.
In this study, hybrid photocatalysts were prepared with the aim of realizing low-concentration hydrogen sulfide gas-phase decomposition under visible light. By combining carbon nitride (g-C3N4), which is responsive to visible light and has a large specific surface area, with metal sulfide photocatalysts, the g-C3N4/CdS catalyst scored to treat 10 ppm of H2S gas to less than 1 ppm. The effectivity of these photocatalysts was higher than the one of the titanium oxide irradiated UV light, and it is considered that the hybrid photocatalysts’ effectivity was promoted by combination of heterojunctional photocatalysts, and its H2S adsorption performance.
Whereas the outlet H2S concentration was increased over time, it was around 3 ppm after 3 h H2S injection. This phenomenon was confirmed for all catalysts in the result, but their gradients varied from catalyst to catalyst. In this study we investigated the catalytic “Poisoning” effect, which is also known as problem of precious metal catalysts, and to prevent the reduction of activity we implemented post treatment and catalytic cycle. The g-C3N4/Mo catalyst was found to be almost unaffected by sulfuric poisoning, with scoring to treat 10 ppm of H2S to nearly 1 ppm. Analyzing the performance of each catalyst evaluated in this study and the effects of poisoning could solve the odor problem in actual H2S emission plants, as well as improve the efficiency of photocatalysis in the gas phase.
References:

[1] M. Dan, S. Yu, Y Li, et al, Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2020, 42, 100339.

[2] Y. Uesugi, H. Nagakawa, M. Nagata, ACS Omega, 2022, 7, 14, 11946.

Figure 1