Returning to U.S. From SYD Through PEK

Hello--I am a U.S. citizen who is traveling to Australia. On the way home I will be traveling from Sydney through Beijing and on to San Francisco. I have an 8 hour layover in Beijing. 1) Am I eligible for the 72-visa free entry to tour Beijing? and 2) Will I still have to register with a local police station since I'm only there for 8 hours? Thank you!