mehrere Kataloge

It is not possible to merge catalogs.  However, there are some workarounds that may be useful for you.

• Convert all of your catalogs to your latest version of Elements.  See this article for converting catalogs created before Elements 13.
• Make sure that all photo keywords have been saved to file.
• If you have created Albums that you wish to preserve in your merged catalog, create a new keyword for each Album and save the keywords to the files. 
• Once, you have performed the above tasks, create a new catalog
• (Optional) Create a new keyword hierarchy in the new catalog and/or Export and Import the keyword hierarchy files from the old catalogs.  Depending on your current hierarchies, this may not be worth doing.  It's hard for me to express an opinion without knowing more about your situation.
•  Import all of your photos into the new catalog. 
• When you import the files to the new catalog, you will be given the opportunity to import the existing keywords.  See this article which shows you what you should do to import the keyword tags into the new hierarchy.
• If you create a keyword hierarchy before importing the files, you are given more control over the import of the keywords into the new catalog.  This may save you some time.  But you can always perform the necessary organization later.

Note that the Organizer's special tags (People, Places, Events) and all related information such as face recognition, will not be transferred to the new catalog.  However, People tags will be converted to keyword tags and will show up under the Imported Keyword tags hierarchy.  It is fairly easy to move these People tags into a new hierarchy.

Note also that Albums will not be transferred to the new catalog.  That is why I suggest that you apply new keywords for them to make it easier to recreate the Albums if that is what you want to do.