I have a US-Passport, with a just used Thai Visa, do I need a Visa?and if so what type?

I am a American flying from Bangkok, to New York, with a Layover in Beijing

I will have a 12.5 hour layover in Beijing, I would like to leave the airport and get a bite to eat, and just look around a little, and try some street food, and take photos. I will only be there for 12 hours, not long at all.

Retyped due to errors LOL