I don't know if we qualify for the 24 or 72 hour visa

but we are US citizens and here are our flight details:

April 15 we fly from Bangkok to Shanghai and arrive at 5:35am

April 16 we fly from Shanghai back to Chicago but we have a layover in Beijing. Here are the details:

8:35am depart Shanghai
11am arrive Beijing
1:40pm depart Beijing for Chicago

What do we qualify for when we land in Shanghai and how should we apply? Please help!

Thanks!