## 1 Introduction  
H\({}_{2}\)S is a colorless gas that is denser than air [1]. It is flammable [2], toxic [3] and highly corrosive [4], with an unpleasant smell of rotten eggs [5]. H\({}_{2}\)S needs to be removed from fuels since it converts to SO\({}_{2}\) during combustion and causes acid rains when released into the environment [6]. Because of these properties, H\({}_{2}\)S removal is a crucial step in gas cleaning and finds application in different industries including coal and biomass gasification [7; 8], biogas production [9] wastewater treatment, food processing and production and other fuel production processes [10]. In most of these applications the concentration of H\({}_{2}\)S is magentarelatively low, i.e., well below 1 vol%. Absorption-based methods to remove H\({}_{2}\)S are used in different reactor configurations, such as packed columns or spray towers. The most common solver is water which, however, cannot remove H\({}_{2}\)S to low concentrations due to the low solubility of H\({}_{2}\)S in water, with the Henry's constant of about 10\({}^{-3}\) mol/(m\({}^{3}\) Pa) at room temperature [11]. Most of the available solvents that have high solubilities for H\({}_{2}\)S require extreme operating conditions, i.e., high pressures and/or low temperatures, which translates into high operating costs [12]. Due to this, absorption based methods, although high in technological readiness, are less favorable for the treatment of diluted gas streams when compared to other technologies. In particular, regarding adsorption based technologies, we find activated carbon as the most common adsorbent available but it has a very low sulfur removal capacity [13]. The adsorption capacity can be enhanced by impregnating the activated carbon with metals, resulting in composite sorbents in which the metal is present in the form of nano-scopic oxide particles [14; 15; 16]. Bio-chars containingdifferent metals, including Ca, Fe and Mn, where found to have similar sulfur removal capacities as composite active carbon materials [17; 18; 19]. This is especially interesting, as bio-chars are obtained from waste materials. Due to the low cost of feedstock and high removal capacities [20], these materials have the potential to be viable sorbents. However, there is limited testing of carbonaceous sorbent materials for high temperature applications. Membrane technology with facilitated transport properties is another alternative to remove H\({}_{2}\)S. However, the complications of operating a membrane process at optimum conditions still makes it an unfavorable alternative at the current development stage [13]. H\({}_{2}\)S can be removed by precipitation techniques as well. A solution containing FeCl\({}_{2}\), FeCl\({}_{3}\) or FeSO\({}_{4}\) can be used to precipitate the sulfur in the form of FeS. Technical complications of operating a continuous process based on this principle aside, the final concentration of H\({}_{2}\)S after treatment remains around 100 ppm which is still high for most applications [21; 22]. Biological processes degrade H\({}_{2}\)S to elemental sulfur have shown a high potential at pilot and demonstration scale plants. Despite being environmentally friendly and economically advantageous, there are still challenges to be addressed [23; 24]. Biological removal of H\({}_{2}\)S can use both photo-trophic and chemo-trophic bacteria to bio-oxidize hydrogen sulfide. The requirement of a light source for photo-trophic bacteria is the main constraint for adapting the technology to the industrial scale [23]. Chemo-trophic bacteria require an oxygen or nitrite source, and if the amount is not at the optimum level, H\({}_{2}\)S tends to convert to sulphates which is not desired [25; 26]. Using metal sorbents to remove H\({}_{2}\)S from diluted gas streams is a common practice nowadays [27].