Short version:

Catalytic convertors contain a catalyst, usually platinum beads, but may be
rhodium or some other very pricy metal.  This catalyst causes a reaction on it's
surface which converts nasties (oxides of nitrogen as monoxides of carbon, etc)
to their fully oxidized (and less harmful) states.  They only work with with
unleaded gas, as leaded gas will coat the catalyst beads with funky junk and
cause the spontaneous reaction to cease.   They are expensive due to the metals
that make them up.

Keith Adams
Calgary, Alberta, Canada
1986 Vanagon GL Westfalia "Roxy"

"Paul M. Hillbish" wrote:

> In a message dated 1/22/01 6:34:42 AM Eastern Standard Time, kdlewis@JUNO.COM
> writes:
>
> <<  For the sake of air
>  quility I desided to fix it. >>
>
> What exactly does the cat do anyway? What I mean is, there appears to be a
> wire screen in there. Is it some sort of filter that it is required for
> emissions? If anyone could enlighten me on the details and specifics on this,
> I would apprecieate it.
>
> --Paul--