Dodge (and other US manufacturers) began installing catalytic converters on their diesel engines as a result of increasingly stringent emissions regulations. There isn't a single year when it happened for all their diesel models. The implementation was gradual, starting in the late 1970s and early 1980s for light-duty trucks and continuing through the decades with increasingly sophisticated systems to meet progressively stricter standards like those under the Clean Air Act.
To find the exact year a *specific* Dodge diesel model got a catalytic converter, you'd need to specify the model and year range. Information can often be found in owner's manuals or through online resources dedicated to vehicle specifications.
