Flight to beijing stay for two nights then flight to south korea

Will I be able to board my flight from Seattle to Beijing without a visa, since I have a booked flight from beijing for south Korea within the 72 hr time-frame from my arrival in china although the flights are from two different airlines? Will I be allowed to leave the airport, get a hotel for the two nights I am there and go visit the great wall during my 72hr transit?
Thank you!