Assembly and method for reducing nitrogen oxides, carbon monoxide and hydrocarbons in exhausts of internal combustion engines

A method of operating a catalytic system for reducing emissions from a rich burn spark-ignited engine, comprising:

• controlling intake air and fuel (AFR) to produce first exhaust gases substantially free of oxygen;
• passing said first exhaust gases into a first-stage catalyst chamber containing a three-way catalyst (TWC) operating above 800° F., which minimizes NOx content by reducing NOx (to N2 and O2), without minimizing CO content;
• passing exhaust gases exiting from the first-stage catalyst chamber to an inter-stage cooling chamber having
• a) cooling means, and cooling by-pass means, which are used to adjust gas temperature to a controlled Tmix=390−520° F., and
• b) secondary air injection means, which enriches the oxygen content to about 0.25-1.0%;
• passing exhaust gases exiting from the inter-stage cooling chamber to a second-stage catalyst chamber containing a catalyst that minimizes CO content by oxidizing CO to CO2, without substantially increasing NOx emissions.