Hello we, husband, wife are departing from phuket, thailand on 12/11/16 @ 130 am

(flight 822 air china and will land in beijing on 12/12/16 7:45 am for 8 hour layover. Our final destination is san franciso, on air china flight 985. our plane leaves at 4:00 pm.

If we want to leave the airport and go site see for 4-6 hours, do we need a visa? If so, how where do we apply. We are on affordable asia tour.