An on-board vehicle reservoir containing an ammonia/organic solvent solution may be associated with a phase separator configured to isolate ammonia from the solution. The ammonia may be introduced into an exhaust gas stream of an internal combustion engine to function as a catalytic reductant. Ammonia may be employed to generate hydrogen via catalytic decomposition of ammonia, and the hydrogen may be introduced into an exhaust gas stream to aid catalytic reactions such as catalytic oxidation of carbon monoxide (CO) and/or hydrocarbon (HC) and/or reduction of nitrogen oxides (NO); for instance during a cold-start period.