Unfortunately, full-text catalogs don't recover very well. A couple of technical articles in the Microsoft Knowledge Base discuss in great detail all the steps required to recover a catalog. There are quite a few steps involved and the database has to be configured in particular ways. The easiest thing to do is simply rebuild the catalog, using the Rebuild option in the Full-Text Catalogs section of Enterprise Manager, or using the system stored procedure. This should take only a minute or two. After the catalog is rebuilt, perform a full population. Once this is done, the catalog is "recovered."
Avoid dropping and then re-creating a catalog. If a catalog reference has been corrupted, which is usually what happens when databases are recovered, the drop stored procedure will not operate correctly. Use the rebuild option to re-create a catalog instead.