72 hour transit, do we need to a tourist visa?

Greetings,

My Wife and I are flying from the USA to Japan for tourism. On the way back to USA we are stopping in Beijing for a few days to visit tourist sites (Great Wall, Forbidden City). It will be less than 72 hours.

Following is our flight dates and destinations/airports.

March 22 USA (MDT, IAD) to Japan (IAD)
March 29 Japan (HND) to China (PEK)
April 1 China (PEK) to USA (ORD, MDT)
Thank you