Passive ammonia-selective catalytic reduction for NOx control in internal combustion engines

A method for operating an internal combustion engine includes controlling the engine to a preferred air/fuel ratio to generate an engine-out exhaust gas feedstream including preferred concentrations of nitric oxide, carbon monoxide, and hydrogen, converting the nitric oxide, carbon monoxide, and hydrogen to ammonia across a first catalytic device; and storing the ammonia on an ammonia-selective catalytic reduction device fluidly serially connected downstream of the first catalytic device.