national capital vs capital of Benin

national capital and capital of Benin both are nouns.

Word	Noun	Adjective	Verb	Adverb
national capital	Yes	No	No	No
capital of Benin	Yes	No	No	No

national capital (noun)	capital of Benin (noun)
the capital city of a nation	the capital of Benin in southwestern part of country on a coastal lagoon