Activate the Cross-Site Publishing feature in SharePoint
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.
To remove contents of a connected catalog from a publishing site, you have to disconnect the publishing site from the catalog.