When running the command:
/kill @e[type=Item] {Item:{tag:{display:{Name:"Portable Tent"}}}}
In the chat window it kills the player running the command not the item.

When running it in a command block this error occurs:
[21:43:36] You must specify which player you wish to perform this action on.

I assume this is because you can't add partial data into the kill command yet. However, it does work with test for.

/testfor @e[type=Item] {Item:{tag:{display:

}}}