The propeller on a prop plane can be attached to either a piston or a jet engine. (Or mostly in smaller or experimental planes, an electric motor)
So, in the example of Porter, those are Dash-8s and that's a jet engine. Yes it has the propellers on the front like those old-timey aeroplanes you saw in black and white, but you'll notice that the propellers are on the front of a jet engine. See, the engine needs spinning blades inside it to work, compressing air to run the engine, but you can choose whether to expend the resulting energy on producing yet more spinning motion for propellers (a turboprop engine) or to shove lots of fast air out of the back (a turbofan engine)
A jet engine does not use leaded gasoline, that would be crazy. Whether it is spinning a propeller or just shoving fast moving air out the back, the jet engine runs on kerosene. This is still nasty stuff, but it does not have lead in it.