# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 18 Transition Metal Oxides  
Catalysts based on metal oxides are most widely used and studied in the continuous process of H\({}_{2}\)S selective oxidation. Their main feature is that they provide a stable operation with different H\({}_{2}\)S/O\({}_{2}\)/H\({}_{2}\)O ratios. Also, undoubted advantages of oxide catalysts are high mechanical and thermal stability, availability, wider ranges of hydrogen sulfide concentrations, and space velocities; therefore, their productivity is much higher than that, for example, of carbon-based catalysts [108]. This group of catalysts is promising for the direct oxidation of hydrogen sulfide due to the previously indicated reasons: high mechanical and thermal stability and availability. Catalysts for gas-phase oxidation of hydrogen sulfide to elementary sulfur are known on bulk alumina or alumina with additives of titania (5.0-15.0 wt.%). The catalysts have high activity, and selectivity in a temperature range of 160-230 \({}^{\circ}\)C: the total conversion of hydrogen sulfide into sulfur and sulfur dioxide is 80-100% depending on the temperature range studied [109]. In the practice of gas-phase oxidation of hydrogen sulfide with air oxygen to elementary sulfur, the use of titania in the form of a mixture of its rutile (5-50 wt.) and anatase (50-95 wt.%) modifications as a catalyst is described. In the presence of the catalyst of the specified composition, it is possible at a space velocity of 3000 h\({}^{-1}\), a temperature of  
Figure 6: The tentative mechanism of sulfur deposition on the surface of a catalyst based on SiC: (**a**) in the presence of water vapor; (**b**) without water vapor (adapted from [106]). 230-280 \({}^{\circ}\)C, an initial H\({}_{2}\)S concentration of 3 vol.% with the stoichiometric H\({}_{2}\)S/O\({}_{2}\) ratio to provide \(\sim\)98-100% conversion of hydrogen sulfide [110]. However, the catalyst of the specified composition has extremely low mechanical strength. The introduction into the catalyst of strengthening additives of magnesium oxide in an amount 0.3-1.0 wt.% and alumina slightly increases the mechanical strength (the catalyst attrition rate decreases by two times). More significant strengthening (4 to 6 times) is achieved by deposition of the active component on the faience aluminosilicate support. The complete kinetic data relating to the oxidation of hydrogen sulfide to elementary sulfur on metal oxides can be found in the works of [PERSON] and [PERSON] [111], who studied more than twenty individual metal oxides under the following standard conditions for all samples:  
T = 250 \({}^{\circ}\)C  
The concentration of reagents:  
C\({}_{\rm H2S}\) = 0.5 vol.%  
C\({}_{\rm O2}\) = 0.25 vol.%  
It was shown that for the kinetic region, an activity row of individual oxides is as follows:  
V\({}_{2}\)O\({}_{3}\) > Mn\({}_{2}\)O\({}_{3}\) > CoO > TiO\({}_{2}\) > Fe\({}_{2}\)O\({}_{3}\) > Bi\({}_{2}\)O\({}_{3}\) > Sb\({}_{6}\)O\({}_{13}\) > CuO > Al\({}_{2}\)O\({}_{3}\) = MgO = Cr\({}_{2}\)O\({}_{3}\)  
Representing the conversion of hydrogen sulfide in the form of three reactions: the Claus reaction (I), the total oxidation reaction (II), and the reaction of partial oxidation (III) [Equations (22)-(24)], [PERSON] and coauthors [112] found the following patterns for individual oxides.