ICI Synetix certainly make Mercury Removal catalyst for hydrocarbon gas - I dont know if it works with oil.
For hydrocarbon gas systems you usually have one large vessels (sometimes duty/standby) filled with catalyst, you measure the DP and sampole that catalyst till you need to change over then you send the catlyst away for reprocessing. Ususally at the outlet of the ctalyst bed you have two (duty/standby) filters 10 micron or so.
ICI contact number ++ 44 1642 553 601, Vince Atma Row
MB