Yes, you can perform backup of catalog database using RMAN with below steps:

1. Start the RMAN with NOCATALOG option.

2. Run the recovery catalog database in ARCHIVELOG mode.

3. set the retention policy to a REDUNDANCY value greater than 1.

4. Backup the database onto two separate media(disk and tape), You can use BACKUP COPIES 2.

5. Donot use another recovery catalog as the repository for these backups.

6. configure the controlfile autoback feature to ON.