My Saturn engine dies more and more often. It happened starting around one
year ago when I waited for a traffic light. I had to restart it. And then,
the engine dies more and more often. Usually, it happened when I made a
turn and waited for a traffic light. These days, even during driving on
highway normally, the engine died sometimes. However, I can always succeed
in restarting the car (sometimes I had to turn the key several times).

A mechanic checked my car, replace the four starter plugs and fuel filter.
The problem wasn't fixed. I knew that catalytic converter of my car   was
also broken. The mechanic told me it could be the problem of "catalytic
converter". But I am wondering "catalytic converter" can cause engine die
during driving.

I do greatly appreciate for any advices or possible solutions to this
problem.

Thank you very much in advance.