# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 17 Catalysts Based on Sic  
Recently, catalytic systems based on new materials are being intensively developed. One of these materials is SiC-silicon carbide. Catalysts supported on silicon carbide are proposed to be used in highly exothermal reactions such as partial oxidation of hydrogen sulfide to sulfur. Recently, several works were published offering catalysts-metal oxides on silicon carbide [105; 106; 107]. The use of SiC as support of hydrogen sulfide oxidation catalysts has several advantages:  
1. The chemical inertness of the material allows the use of catalysts in aggressive media, providing high stability of catalysts;
2. High SiC thermal conductivity (150 W/m\(\cdot\)K) compared to alumina (15 W/m\(\cdot\)K) ensures a uniform temperature distribution in the catalyst bed and prevents local overheating of the catalyst;
3. SiC-based catalysts can be used to remove H\({}_{2}\)S from highly concentrated gases (>2 vol.%);
4. The meso- and macroporous SiC structure allows the use of catalysts for the oxidation of hydrogen sulfide at temperatures below the dew point or in the presence of excess water. [PERSON] and co-workers [105] investigated Fe\({}_{2}\)O\({}_{3}\)-based catalysts supported on \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and SiC in the oxidation reaction of 1 vol.% H\({}_{2}\)S in the presence of 30 vol.% H\({}_{2}\)O. It was shown that the SiC catalyst had much higher activity in the hydrogen sulfide oxidation reaction compared with the alumina-based catalyst. The Fe\({}_{2}\)O\({}_{3}\)/SiC catalyst showed high activity in the hydrogen sulfide oxidation reaction and selectivity to the formation of elemental sulfur in excess of oxygen and in the presence of water vapor. To determine the nature of the active component, Fe\({}_{2}\)O\({}_{3}\)/SiC, FeS\({}_{2}\)/SiC, and FeSO\({}_{4}\)/SiC catalysts were synthesized [107]. It was shown that at H\({}_{2}\)S conversion close to 100%, the selectivity to sulfur on these catalysts decreases in the following sequence:  
\[\mathrm{FeSO_{4}/SiC>Fe_{2}O_{3}/SiC>Fe_{2}/SiC}\]  
The catalyst containing sulfate groups on the surface showed selectivity to sulfur of about 100% at 240 \({}^{\circ}\)C, whereas the formation of SO\({}_{2}\) was observed on the other catalysts in noticeable quantities. For example, on the FeS\({}_{2}\)/SiC catalyst, the selectivity to sulfur was about 60%. [PERSON] and co-authors [106] proposed to use for the oxidation of hydrogen sulfide in the presence of water vapor NiS\({}_{2}\)/SiC catalyst supported on mesoporous SiC. To avoid the catalyst deactivation in the reaction conditions, it was proposed to use a binary catalyst containing the hydrophobic SiC support and the hydrophilic layer of SiO\({}_{2}\) located in the support pores of the carrier. The transformation of the initial NiS\({}_{2}\) to nickel oxysulfide which has high activity in the hydrogen sulfide oxidation reaction explains the high activity of the proposed catalyst. The mechanism of the catalyst deactivation in the absence of water vapor was proposed and an explanation of the high stability of the catalyst in the presence of water was found (Figure 6). According to the authors, the catalyst has a hydrophilic layer in SiC pores. Under the reaction conditions, in the presence of water vapor, the water film is formed on the hydrophilic layer, which delivers/transfers the resulting elemental sulfur to hydrophobic parts of the SiC support, where its deposition and the subsequent transition to the gas phase occurs. Thus, the active component remains available for reagents, and the catalyst is not deactivated (Figure 6a). In the reaction medium without vapor water, such a film is not formed. Therefore, sulfur deposition occurs mainly on the active component of the catalyst, which leads to the capsulation of the active component and deactivation of the catalyst (Figure 6b). Thus, SiC catalysts are promising for use in the reaction of partial oxidation of H\({}_{2}\)S to sulfur. Several SiC-based catalysts were proposed.