The sentence I came across,
The Qing regime still saw itself as supreme on the planet.
I might regard the word "supreme" as a noun because it follows a preposition word "as". But if it's a noun, I think it should be "a supreme". What's more, I find the word "supreme" is rarely used as a noun nowadays.
Then I pay attention to "as" here. Now I am not sure if it is a preposition.