To be able to enable a library or list as a catalog, you have to activate the Cross-Site Collection Publishing feature.
Make sure that you’re a site collection administrator on the site collection that contains the library or list.
On the top-level site of the site collection, from Settings , select Site settings.
On the Site Settings page, in the Site Collection Administration section, select Site collection features.
On the Site Collection Features page, next to Cross-Site Collection Publishing, select Activate.
Notes: If you deactivate the Cross-Site Collection Publishing feature, this doesn’t remove the contents of a connected catalog from the publishing site. By deactivating this feature, you’ll no longer be able to modify existing catalog settings, or connect publishing sites to catalogs from the site collection.
To remove contents of a connected catalog from a publishing site, you have to disconnect the publishing site from the catalog.