Many of them are not built strong enough to just hang on the wall without support from above. Some are not 'finished' on the top horizontal surface. Most of those that are recirculating, have a removable plug so you can actually vent them outside. You'd need to find one that would let you vent directly out the back. What you may find as difficult is fabricating an air-tight fitting that would transition to something you could fit a vent cap on outside on the wall that also has a damper in it to prevent the hood from becoming a direct open hole to the outside. While I heartily concur venting to the outside is preferable (and mine is), keeping that sealed off and transitioning to a termination out there can be problematic, especially if the wall depth is 2x4 construction. There are some designed to hang and the decorative duct comes out the top, then turns to go out through the wall, but the pipe diameter is pretty large. Mine was particularly troublesome, as iit required an 8" round outlet, but then it has a pretty large motor that could lift your toupe on high if you aren't careful!
Sorry I can't recommend something...I'm sure there's some out there.