Why can't export mailbox to PST

Hello,

Exchange sever 2013 on srver 2012R2:

The term 'New-MailboxExportRequest' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:25
+ New-MailboxExportRequest <<<<  -Mailbox username -FilePath C:\Temp\name1.pst
    + CategoryInfo          : ObjectNotFound: (New-MailboxExportRequest:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

Thanks for your help.