So, just as a reference here are the keys we're currently seeing as ones that will not be converted to gold or removed upon release of the patch -- if you have them they'd be put back into your normal inventory. This isn't necessarily a final list, and it's possible we could cut the list down even further before 4.2 releases.
Chave do Glutão Implacável (BRD)
Secret Safe Key (BRD)
Chave do Guardião Sombrio (BRD)
Chave da Arca de Relíquias (BRD)
Jump-a-Tron 4000 Key (Nagrand)
Chave do Butim de Kolkar (Barrens quest)
Chave da Prisão de Etéreum (Netherstorm – Blade’s Edge)
Chave do Capitão (Tanaris)
Any Blacksmith keys (e.g. Titanium Skeleton Key)