Hydrogen sulfide (H2S) originated from many sources, like natural gas, coal chemical industry, wastewater treatment plants, landfill sites, petrochemical industry, is regarded as a key air pollution problem (Lin et al. 2021; Andrade et al. 2020; Tian et al. 2021). H2S with malodor is pernicious to human health and has many disadvantages on a large quantity of catalysts. The exposed concentration beyond 500 ppm causes a loss of consciousness (Azargohar et al. 2011). The conventional methods for H2S treatment contain the biological treatment (Barbusinski et al. 2021), wet scrubbing (Wang et al. 2020), low temperature plasma technology (Feng et al. 2021), advanced oxidation (Gao et al. 2022), special activated carbon adsorption (Ning et al. 2018; Shen et al. 2018; Li et al. 2022). Among these methods, adsorption is one of the most effective methods for deodorization and has been widely used. In a wide range of adsorbents, activated carbon is used frequently and many studies have been reported on H2S adsorption (Li et al. 2020; Boudou et al. 2003; Bagreev et al. 1999; Subrenat et al. 2008). However, it is rather difficult to adsorb H2S effectively by pure activated carbon, because activated carbon owns non-polar surface while H2S is a polar gas (Chen et al. 2003).
H2S is an acidic gas and has strong reducibility, which is easy to be oxidized or reacted in the presence of catalysts. Because of activated carbon with developed pores and huge surface area, it is widely used as the support and can be modified easily (Georgiadis et al. 2020; Yang et al. 2020; Zeng et al. 2020; Ciahotny et al. 2019). In order to improve the H2S adsorption performance, the activated carbon can be loaded with various catalysts to achieve this. Alkaline is a general catalyst, the mechanism of which is involved H2S dissociation into HS− and H+ in the alkaline environment and then the formed HS− was further oxidized into S, SO2, SO42− by adsorbed oxygen (Sitthikhankaew et al. 2014; Choi et al. 2008; Brazhnyk et al. 2007). The catalysts content and categories are investigated to evaluate the catalytic performance. Based on the above mechanism, it can be concluded that continuous H2S dissociation into HS− or S2− would result in accelerating H2S adsorption and the improvement of oxidation process would lead to enhance the H2S catalytic conversion on the adsorbent. From this aspect, KI and KMnO4 were selected as the assistant catalysts added with a little amount to investigate catalytic synergy. KI and KMnO4 were not expected to react with H2S, but they were applied to act as the catalyst for continuous H2S dissociation and enhancing oxidation.
Activated carbon as a support is prepared by different materials and methods, the pore structure of which has important effects on the catalytic performance of the catalysts loaded on the carbon (Zhang et al. 2017; Song et al. 2019; Hu et al. 2006). Generally, activated carbon with large pore volume can not only be beneficial to fill more catalysts, but also provide sufficient pore volume exists to store reaction products. Three kinds of commercially available coal-, and coconut shell-based activated carbons were chosen as adsorbents, which are produced by steam activation. The same catalyst content is loaded on each of the three activated carbons in order to investigate the effect of the pore structure of activated carbons on catalytic performance.
In addition, gas stream properties also have important effects on the catalytic performance. At dry or moist conditions, oxygen or oxygen-free conditions, the differences of the catalytic performance are investigated. The effects of organics on catalytic performance are analyzed from two aspects: pre-saturated catalytic carbon for H2S adsorption and catalytic carbon for H2S adsorption accompanied with organic.