In order to grant EXECUTE permission on all Stored Procedures of a database to a user we can do it in several ways one way is...
To achieve this we can create a user defined role and grant it the EXECUTE permission and then add the user we want to grant the EXECUTE permission.
User Defined Role Creation:
Create role SP_Executor
Granting EXECUTE permission to the role created:
Grant EXECUTE to SP_Executor
Add user to the role :
Exec SP_Addrolemember 'SP_Executor','DomainName\UserName’