FeS catalysts are used in a variety of applications, including:

Hydrodesulfurization (HDS): FeS is used as a catalyst in the HDS process to remove sulfur from petroleum products.
Hydrodenitrogenation (HDN): FeS is used as a catalyst in the HDN process to remove nitrogen from petroleum products.
Hydrocracking: FeS is used as a catalyst in the hydrocracking process to convert heavy hydrocarbons into lighter hydrocarbons.
Fischer-Tropsch Synthesis: FeS is used as a catalyst in Fischer-Tropsch synthesis to convert synthesis gas to hydrocarbons.
Coal Gasification: FeS is used as a catalyst in the coal gasification process to convert coal into synthesis gas.
Water Splitting: FeS is used as a catalyst in the process of water splitting to split water into hydrogen and oxygen.
FeS is a versatile catalyst that can be used in a variety of applications. It is a relatively cheap catalyst and easy to handle. FeS is also a safe catalyst that does not produce any harmful by-products.

However, FeS is not without its drawbacks. It is a relatively active catalyst and is easily poisoned by impurities in the raw materials. FeS is also a relatively unstable catalyst that deactivates over time.

Overall, FeS is a valuable catalyst that can be used in a variety of applications. It is a relatively cheap catalyst that is easy to handle and safe to use. However, FeS is a relatively active catalyst that is easily poisoned and deactivated.