Airport transfer in Beijing for Iranian - need for visa?

I am and Iranian

I am travelling from Korea through Beijing and Urumqui to Tehran with China Southern Air:
Departure: 08 July 12:30 Seoul,
Arrival from Seoul:08 July 13:35 Beijing, (Capital Intl)
Departure: 08 July 14:40 Beijing, (Capital Intl)
Stop: Urumqi, (Diwopu Intl)
Arrival 08 July 22:00 Tehran, (Imam Khomeini Intl)

Do I need visa for the transfer in Beijing?

Thank you!