From the Fitch FAQ:
Q. How does the catalyst work?
Refineries cannot remove many poorly performing molecules to make a more ideal fuel. In addition, once fuel leaves the refinery or is stored it is subject to attack by oxygen, ozone, and microorganisms (bacteria, yeast, and mold) that grow in the fuel. All these processes degrade the fuel to make a poorer product that prevents engines from performing at optimum levels. The Fitch Fuel Catalyst reformulates fuel prior to combustion on board the vehicle, preventing oxygen and most diseases from attacking the fuel and reversing any degradation that may have occurred prior to the fuel being introduced to the vehicle. The Fitch Fuel Catalyst assists the combustion process by insuring that fuel is highly uniform, potent, consistent, and stable.