Well if this helps any...

On my 99 Sonata (v6...not that it matters) I tried the same thing, with
the impact wrench- didn't work.  I ended up trying to hold the engine from
turning while I used a breaker bar by putting something through the cam
sprocket to help the old timing belt to help stop the turning- big
mistake.  DON'T do it by putting something in the cam like I did- it
broke.

Anyway, on to your problem... I ended up using a breaker bar and a piece
of wood and a large screw driver to jam against the pully and the end in
the wheelwell (to stop it from turning) and then cranked the bolt off.  By
the way, mine was standard thread out (lefty loosy, righty tighty)... so
counter clockwise out.  

It was as if the bolt was coroded to the pully (may be that's just our
weather in WI though)

Good luck.

It's a right-hand thread. Make sure your impact wrench delivers at
least 200 ft/lbs. Some of the cheaper 1/2" electric models just aren't
strong enough. And a lot of torque is lost because the crankshaft is
free to turn.

Try alternating between tightening and loosening the bolt, 10 seconds
at a time, in order to break the threads free. It can take up to five
minutes before the bolt comes loose. Allow the impact socket to
cool down if it gets too hot.

Bob