1.2.1Two - way or oxidation catalytic conver torEarly converters, called “Two-Way” (or oxidation) catalytic converter converts harmful carbon mono xide (CO) and hydrocarbons (HC) produced by the relatively inefficient, low compression engines of the day to harmless carbon dio xide (CO2) and water with the assistance of a precious metallic catalyst. This process “converts” these harmful gases into water vapour and harmless carbon dioxide (CO2). But these converters have little effect on nitrogen oxides (NOX) and particulate matter. It is important to understand that Two-way converters are most effective when used with engines that have a lean air/fuel mix, because this condition provides ample o xygen to “burn” the pollutants.