This is not possible within CMS. Workflows only apply to specific content types and content authors. There is currently not a way to apply them to folders. However, you can set up Folder Reviewers, which may be the next best thing to have certain people receive the approval notifications.

For more information on Folder Reviewers:
  1. In the top right go to Help
  2. Search for CMS Assigning or Removing Folder Reviewers
  3. Click on Managing Folder Permissions - Convio Online Help
  4. Click on Assigning or Removing Folder Reviewers