Addition of hydrogen significantly increases the amount of stored nitrogen oxides (NOx) over Pt/Ba/Al2O3 at 100 A degrees C and Ag/Al2O3 between 100 and 200 A degrees C. This increase is unique for hydrogen as reductant. A higher apparent NOx storage capacity is also observed by simultaneous reduction of NO in a selective catalytic reduction (SCR) reaction, where, however, the conversion in H-2-SCR is < 10 % in this study.