If you want to execute e.g. "/kill @e Item {Item:{id:hopper}}", it will not work. The hopper will still stay as item entity in the world.
Comments 4
Command is wrong, command is supposed to be "/kill @e[Type=Item]", However i think you are unable to specify item type/id.
FOUND A SOLUTION: Click
Malformed command please review the format of the kill command.