My dd moved to 2 naps around 8 months. It was gradual - some days she just didn't want to go down for the late afternoon catnap - and when she didn't have it, she seemed ok. She started being able to have a longer stretch between her morning and afternoon nap too (closer to 1 or 2 pm rather than 12) so I finally just stopped trying for the last nap. If she was grumpy (short naps, or earlier afternoon nap), I'd move her bedtime a little earlier that day.