Il have 12 hours between flights at capital airport

Well, you can make full use of these hours to tour around downtown area. You can take airport express to Dongzhimen Station first. Then take subway line 2 to Qianmen Station, Exit A. Then walk north to tour around Tiananmen Square and Forbidden City. After touring around, you are suggested to go to Wangfujing Avenue if you have enough time. You can taste many local snacks there. And you can buy some interesting souvenirs.