Merchant banks are Banks that gives loans, offer financial advisory, fundraising and investmeet for Large scale company and also highly wealthy individual's.
Merchant banks unlike commercial banks do not provide services to the general public rather it services are streamlined for specific persons and company. Merchant Bank can also be called investment bank.
Here is a list of the 5 licensed merchant Banks in Nigeria,their addresses and official website.

https://ogbongetech.com/2020/02/merchant-banks-in-nigeria-licensed-by-cbn/