Name a non-metal used to convert vegetable oil into vegetable ghee.

Nickel is the common catalyst, but it is a metal. For non-metal, finely divided palladium and nickel are metals; the non-metal used is hydrogen as reactant is non-metal. Hydrogenation of oils uses hydrogen gas (a non-metal element) and a metal catalyst like Ni. The question often expects “nickel” as catalyst, but strictly it is a metal. If asked for a non-metal involved, answer “hydrogen.”