I will answer your question with regards to Visual Studio 2012, as this code keeps changing with different versions.
Most designer commands can be assigned using the Tools/Options menu, and going to the keyboard area. However certain shortcuts are hard coded. The shortcut keys are explained in the documentation, the section: VG.net User's Guide/Picture Designer Commands/Picture Designer Default Shortcut Keys.
From there we see the zoom and pan are hard-coded shortcut keys:
Shortcut Keys, Description
CTRL + PLUS Zooms in.
CTRL + MINUS Zooms out.
CTRL + ZERO Zooms to 100%.
CTRL + HOME Pans to center the selected Elements. If no Elements are selected, pans to center the entire Picture.
The remainder of the shortcut keys can be reassigned, using the command names provided on that page. If there are other commands missing from that page, I can look up the command name.
The keyboard focus must be on the Picture Designer to get the correct behavior.