Mechanical apparatus having a catalytic NO

x x x x x x 2 x 2 x x A mechanical apparatus including a combustion engine, a conduit for transporting an exhaust stream away from the engine, a first catalytic NOstorage and conversion region disposed along the conduit, and a second catalytic NOstorage and conversion region disposed along the conduit at a location downstream from the first catalytic NOstorage and conversion region is disclosed. Each of the first catalytic NOstorage and conversion region and the second catalytic NOstorage and conversion region includes at least one catalytic metal configured to convert NOto NOwhen the engine is supplied a lean air/fuel mixture, and at least one NOadsorbing compound configured to adsorb NOfor storage when the engine is supplied a lean air/fuel mixture, and wherein the one of the first and the second catalytic NOstorage and conversion regions has a lower concentration of catalytic metal than the other of the first and second catalytic NOstorage and conversion regions.