I was wondering, if fuel gets in the catalytic converter, how does it damage it?
A catalyst is a chemical that contributes in a chemical reaction but remains unchanged after the whole reaction is complete. In a catalytic converter platinum is the catalyst that converts unburned hydrocarbons into H2O and CO2. If there is too much unburned hydrocarbons going into the catalytic converter, it greatly increases the temperature inside the converter. This increased temperature causes the platinum to be oxidized into platinum oxide, thus eliminating the platinum catalyst.
In addition to what Bill Oertell mentioned excess unburnt hydrocarbon when passing through a hot catalytic convertor create a secondary combustion chamber that melts the insides and the resulting fragments then block the flow of exhaust. When this happens the engine will not start until the problem is rectified. It sounds like rocks inside the cat. This happened to a friends Ford F-150 (both cats)