# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 18 Transition Metal Oxides
2H\({}_{2}\)S + SO\({}_{2}\)\(\leftrightarrow\) 2H\({}_{2}\)O + 3/nS\({}_{n}\)  
2H\({}_{2}\)S + 3O\({}_{2}\)\(\rightarrow\) 2H\({}_{2}\)O + 2 SO\({}_{2}\)  
2H\({}_{2}\)S + 3O\({}_{2}\)\(\rightarrow\) 2H\({}_{2}\)O + 2/nS\({}_{n}\)  
It was shown that for the kinetic region, an activity row of individual oxides is as follows:  
V\({}_{2}\)O\({}_{5}\) > 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\({}_{3}\)  
Whereas for the total conversion of hydrogen sulfide to sulfur and sulfur dioxide (II + III) these oxides can be arranged in the following row [111]:  
V\({}_{2}\)O\({}_{5}\) > Bi\({}_{2}\)O\({}_{3}\) > Fe\({}_{2}\)O\({}_{3}\) = CoO > Mn\({}_{2}\)O\({}_{3}\) > Sb\({}_{6}\)O\({}_{13}\) = TiO\({}_{2}\) > CuO > Cr\({}_{2}\)O\({}_{3}\) > Al\({}_{2}\)O\({}_{3}\) > MgO  
The maximum stationary activity in all reactions (I-III) is observed for vanadia V\({}_{2}\)O\({}_{5}\). Analyzing the data on selectivity, [PERSON] and co-authors [111] concluded that the most selective catalysts for the process (III) are V\({}_{2}\)O\({}_{5}\), MgO, and Mn\({}_{2}\)O\({}_{3}\), while the oxides of Bi, Fe, and Cu are catalysts for deep oxidation of hydrogen sulfide to SO\({}_{2}\) (II). The above series of activities are significantly different from similar ones given by [PERSON] and [PERSON] [37] who studied the catalytic properties of metal oxides of the IV period to select the optimal catalyst for the partial oxidation of hydrogen sulfide. According to their data, the catalytic activity of individual oxides in the reaction of direct selective oxidation of hydrogen sulfide to elementary sulfur at temperatures of 280-300 \({}^{\circ}\)C decreases in the following sequence:  
C\({}_{\rm O3}\)O\({}_{4}\) > V\({}_{2}\)O\({}_{5}\) > Fe\({}_{2}\)O\({}_{3}\) > Mn\({}_{2}\)O\({}_{3}\) > CuO > TiO\({}_{2}\) > ZnO > NiO > Cr\({}_{2}\)O\({}_{3}\)  
They also give the activity row of these oxides in the reaction of deep H\({}_{2}\)S oxidation to sulfur dioxide:  
C\({}_{\rm O3}\)O\({}_{4}\) > V\({}_{2}\)O\({}_{5}\) > NiO > ZnO > CuO > Fe\({}_{2}\)O\({}_{3}\) > TiO\({}_{2}\) > Cr\({}_{2}\)O\({}_{3}\) > Mn\({}_{2}\)OUnfortunately, it is impossible to determine the causes of discrepancies, since in [39], absolute values of the specific rates and the conditions for conducting experiments are not given: the ratio of reagents, the size of the catalyst pellet, etc. [PERSON] and co-authors [113], studied the catalytic activity of transition metal oxides deposited on \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) under the conditions listed below:  
* The content of hydrogen sulfide in the feed, vol.% 20;
* Gas hourly space velocity, h\({}^{-1}\) 7200;
* Hydrogen sulfide/oxygen polar ratio 2/1;
* Temperature range of testing, \({}^{\circ}\)C 200-300;
* The geometric shape of catalysts spherical granules;
* Active component individual oxides of cobalt;
* manganese, chromium;
* Vanadium;
* The active component content, wt.% 0.1-0.6. It was shown that with the stoichiometric ratio of reagents, the activity of metal oxides decreased in the following sequence:  
* Co \(>\) V \(>\) Fe \(=\) Cr \(>\) Mn \(>\)\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) (at T \(>\) 250 \({}^{\circ}\)C);
* V \(>\) Fe \(=\) Cr \(>\) Co \(>\) Mn \(>\)\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) (at T \(<\) 250 \({}^{\circ}\)C). CeO\({}_{2}\)-based catalysts are potentially suitable for H\({}_{2}\)S-selective oxidation, but their practical application is limited due to the problem of sulfate formation. Shape-specific CeO\({}_{2}\) nanocrystals (rods, cubes, spheres and nanoparticles) with well-defined crystal facets and hierarchically porous structure were successfully synthesized and used as model catalysts to study the structure-dependent behavior and reaction mechanism for H\({}_{2}\)S selective oxidation over ceria-based catalysts. It is deduced that the defect sites and base properties of CeO\({}_{2}\) are intrinsically determined by the surface crystal facets.