It is not obvious to me that you can “mix” ReaxFF parameter sets (for example, this capability is not mentioned in the documentation).
Moreover, it is not obvious to me that a ReaxFF treatment is justifiable for an ionic liquid-gold interface – I’m not sure what chemical reactions you’re hoping to observe.
With electrostatics, you mainly need to account for the polarisability of the ions (using either explicit polarisability or scaled charges) and the gold (which can be done with constant potential molecular dynamics, like in the ELECTRODE package); charge transfer between ions, or between ions and gold, is pretty minimal compared to those effects.