Yes, catalytic converter would be a good place to start I suppose... have it checked.

Second, change the air filter.... definitly.

Also, I would have these simple & cheap things done:

Change the fuel filter.
Change the spark plugs (Copper ONLY, NO Platinum).
Run some Techron (Fuel Injector cleaner) through the fuel system.
Make sure the oil & filter were recently changed.

Off topic, but I would have the trans fluid changed if it hasn't been done so in more than 30k miles. This I leave to the MERCEDES DEALER ONLY... it's $110 well spent.

Good luck!! You've got an amazing car!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)