13 hour layover in PEK going to HKG then back to PEK for 3 days

I am traveling to PEK and will stay at a hotel for one night and then travel to Hong Kong the next morning and stay with friends for 8 days and then fly back to PEK and stay with other friends for 4 days and leave for Seattle from PEK.
What should I do about a visa since I have an initial 12 hour layover and then will come back for 4 days?
Thanks