Do I need a transit visa?

I will travel to Japan. On the way back to Barcelona, I will have a 24-hour stopover in China.
I have a Moldovan passport, but I live in Spain.
I need to know, if for this 24h stopover in China, a visa is needed.
I have consulted with the Chinese consulate and Embassy, but they have told me that I have to request this information from the airline.
Can you tell me if I need a visa or not for this stopover? We're not going to leave the airport.
Thanks a lot