# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 5 Catalytic Stage of the Claus Process. Catalysts Used  
Gases from the Claus furnace condenser located after the waste heat boiler containing mainly H\({}_{2}\)S, SO\({}_{2}\), N\({}_{2}\), CO\({}_{2}\), H\({}_{2}\)O, COS, CS\({}_{2}\), CO, H\({}_{2}\), and traces of sulfur are further passed to the main catalytic stage. The process is usually carried out in the adiabatic fixed beds of the granular catalyst, in which, in addition to the Claus reaction, hydrolysis reactions of sulfur-organic compounds also proceed [17; 19; 20; 21; 22]. Catalytic convertors:  
\[2\mathrm{H}_{2}\mathrm{S}+\mathrm{SO}_{2}\leftrightarrow 2\mathrm{H}_{2} \mathrm{O}+0.5\mathrm{S}_{6} \tag{10}\]  
\[\mathrm{COS}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{S} \tag{11}\]  
\[\mathrm{CS}_{2}+2\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{CO}_{2}+2\mathrm{H} _{2}\mathrm{S} \tag{12}\]  
\[2\mathrm{H}_{2}\mathrm{S}+\mathrm{SO}_{2}\leftrightarrow 2\mathrm{H}_{2} \mathrm{O}+0.5\mathrm{S}_{6} \tag{13}\]  
The most commonly used catalyst for the Claus process is aluminum oxide with various modifications. The production of catalysts for the Claus process reaches hundreds of thousands of tons; the big players in this market are BASF [23], producing Claus catalysts Activated Alumina\(-\)DD-431, Promoted Alumina DD-831, EURO SUPPORT (previously Kaiser Alumina), and their successors LaRoche and UOP [24], producing catalysts S-2001/ESM-221, S-501/ESM-251, Axens [25] alumina catalysts CR 3-7, CR-400, CR-35.  
A new generation of Claus catalysts based on titanium dioxide [26] is now being actively implemented. The CRS-31 catalyst of French companies Rhone Poulenc and Elf Aquitaine (the current name is Axens Procatalyse, Paris, France) has gained broad recognition. Experience with its industrial use has revealed high stability for a long time in the presence of oxygen, high activity in the Claus reaction, and COS and CS\({}_{2}\); see also [25; 27].  
At the Boreskov Institute of Catalysis SB RAS, the activities of the oxides of various metals in the Claus reaction were comparatively studied [27; 28]. Twenty-one oxides were investigated, of which nine were stable. These metal oxides can be arranged according to activity per surface area as follows:  
\[\mathrm{V}_{2}\mathrm{O}_{5}>>\mathrm{TiO}_{2}>\mathrm{Mn}_{2}\mathrm{O}_{3}> \mathrm{La}_{2}\mathrm{O}_{3}>\mathrm{CaO}>\mathrm{MgO}>\mathrm{Al}_{2}\mathrm{ O}_{3}>\mathrm{ZrO}_{2}>>\mathrm{Cr}_{2}\mathrm{O}_{3}\]  
The surface activity of vanadium pentoxide is 16 times higher than that of titanium dioxide and 73 times higher than that of \(\gamma\)-alumina. However, pure V\({}_{2}\)O\({}_{5}\) has a low value of specific surface area, and, in connection with the activity per unit of mass, it is inferior to TiO\({}_{2}\) and approximately equivalent to Al\({}_{2}\)O\({}_{3}\). Furthermore, vanadium pentoxide is not very effective in the hydrolysis reaction of sulfur-organic compounds. However, its use in mixed catalytic systems is promising. Based on V\({}_{2}\)O\({}_{5}\) at the Boreskov Institute of Catalysis SB RAS, the ICT-27-36 catalyst was developed. This catalyst is characterized by high activity in Claus and hydrolysis reactions, high stability at operation in oxygen-containing mixtures, and high mechanical strength [29].