transit between South Korea - Beijing - Amsterdam - Portugal (Portugal my final destination)

I hold two passports. South African and Portuguese passport. I've been living in South Korea, so I have a Korean visa in my South African passport. I'll be leaving South Korea for Lisbon next week.
1- I want to know if I can enter Beijing (PEK) on my South African passport without having to get a transit visa?

2- Or is it possible to enter on my Portuguese passport even though I won't have an exit stamp in it from South Korea?

I'm trying to figure this dual passport system out, it's proven slightly complicated. I will be grateful for any advice.
Alex