Not Sipyloidea sp. - looks like Trachyaretaon brueckneri (an unwinged species, and one of my favourite phasmids!). Certainly Heteropterygidae of some sort.
EDIT: I was only at Planckendael in September, but can't remember which species they had!
Thank you for this correction Maguari ! I just took some pictures of the animals and the sign, believing the zoo would know which species they had on display
Thank you for this correction Maguari ! I just took some pictures of the animals and the sign, believing the zoo would know which species they had on display