Effect of calcination temperature on the physicochemical and catalytic properties of FeSO4/SiO2 in hydrogen sulfide oxidation

The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO4 and on their catalytic properties in selective H2S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mossbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400-500A degrees C. This compound contained Fe3+ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600A degrees C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the E >-Fe2O3 modification (the average particle size of 3.2 nm) after treatment at 900A degrees C. As the calcination temperature was increased from 500 to 700A degrees C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere.