24 Hours Visa. Ping

I am Thai holding Thai passport with a US entry permit. I had made a reservation from BKK-PEK via Air China and PEK-ORD via Hainan Airlines. I heard that Thai passport can apply 24 hours free transit since Air China flight arrives at T3 but Hainan Airlines flight departs at T2. But someone said i have to apply the Visa. I would like to ask whether we have to apply the Chinese entry permit?

I'm so curious that i might got rejected from the immigration.