Its cant be done though Joe. You can only kill off emissions so far before you start to seriously comprimise power and cost.
Its like everything in life, you can only go so far, and then you will hit limits. Like CPU's can only reach around 3.8Ghz before transistor leakage is far too high to actually produce anymore power.
The catalytic convertors are already in place, we have removed the lead, fuel is generally a lot cleaner and more refined as are car engines, they are already squeezing every last metre out of fuel atm in modern cars, we cant go much further.
We have been running engines on petrol/diesel for the last 100 years, the last 30 of which we have been trying to clean them as much as we can. We have hit a brick wall now, the limits are close.
Its alright to say we should develop more and more eco-friendly conventional engines, but theres also the question on who is going to fund it? Why should the likes of BMW pay the billions to fund research into cleaner engines, that will hardly make any difference, and that they will never make back?