catalyst

in solvent extraction
https://doi.org/10.1351/goldbook.C00877
A substance included in the solvent to increase the rate of transfer without affecting the position of equilibrium. The term accelerator may also be used but kinetic synergist is not recommended.
Source:
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2380 (https://doi.org/10.1351/pac199365112373)