Welcome to iMore! The following devices will run macOS Sierra:
iMac (Late 2009 & later)
MacBook Air (2010 or newer)
MacBook (Late 2009 or newer)
Mac mini (2010 or newer)
MacBook Pro (2010 or newer)
Mac Pro (2010 or newer)
Check here for more info: http://www.imore.com/macOS-12