Poisoning occurs when the catalytic converter is exposed to exhaust fumes containing substances that coat the working surfaces, encapsulating the catalyst so that it cannot contact and treat the exhaust. The most notable contaminant is lead, so vehicles equipped with catalytic converters can only be run on unleaded petrol. Other common catalyst poisons include manganese primarily from the petrol additive MMT, and silicon which can enter the exhaust stream if the engine has a leak allowing coolant into the combustion chamber. Phosphorus is another catalyst contaminant. Although phosphorus is no longer used in petrol, it (and zinc, another low-level catalyst contaminant) was until recently widely used in engine oil antiwear additives such as ZDDP. Beginning in 2006, a rapid phaseout of ZDDP in engine oils was begun.
Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or sublimate the contaminant, removing it from the catalytic surface. However, removal of lead deposits in this manner is usually not possible due to lead's high boiling point.
The oxygen sensor suffers by similar "muting" through surface contaminant of lead causing incorrect feedback readings, ergo incorrect fuel mapping from the Engine Management.
So, although you are likely to damage the Catalytic convertor through extended use of leaded fuel, you would never notice any difference as emission tests are not carried out on motorcycles(yet) nor do motorcycles have post convertor Oxygen sensors (yet)but you would probably benefit from replacing the Oxygen sensor and as BMW Motorcycles use a standard 4 wire Zirconia with standardised threads, these are available from as little as £14 as a pattern part.
