A selective catalytic reduction (SCR) system includes an on-board ammonia generation system that produces nitrogen from air and hydrogen from a source of a hydrogen-containing compound, and generates an ammonia product from the nitrogen and hydrogen to provide the ammonia product into an exhaust from a NOx generator to reduce the NOx in the exhaust. Oxygen from one or both of the nitrogen generator and the hydrogen generation cell can be supplied to the NOx generator for cleaner combustion or to a particulate filter for cleaning the filter. H2O from the NOx generator can at least partially provide a water source for the hydrogen generation cell.