transit in Beijing or shanghai from Europe to Japan

I will travel from Europe to Japan (Lisbon-Tokyo flight) and the best flight tickets are from Air China. They stop in Beijing (for the flight to Japan) and Shanghai (for the return flight from Japan). We have Portuguese passports for some of us and French passports for the rest. The transit period should be less than 24 hours. Can you confirm that we will not need any visa. Thanks for your help.
Best wishes