It's hard to say, exactly, what the clean, low-carbon cars of the future will look like, but most of the hype revolves around plug-in electric cars and hydrogen vehicles. And why not? Those are both nifty ideas. Yet some of the technology involved still needs plenty of tinkering—plug-ins are at least several years away from becoming a mass-market item, while hydrogen vehicles are going to require a few major breakthroughs before they ever catch on. So it's worth paying attention to other, less-ambitious car technologies, too.

And here's an interesting one: Chemical engineers at GM appear to have discovered how to make a cheap diesel catalyst (the research was written up in the latest issue of Science). Why would that be useful? In general, diesel engines are more fuel-efficient and emit less CO2 than their gasoline counterparts. The catch is that they're also dirtier in some respects and emit more pollutants that produce smog. Mopping up those pollutants can be pricey—often adding as much as $5,000 to the cost of an engine. So there's a trade-off.

Now, in the United States, we tend to have stricter smog standards and relatively weak fuel-economy standards, so gasoline engines dominate the marketplace. By contrast, many EU countries are the reverse—tougher on fuel-efficiency, wimpier on smog—and diesel engines are a lot more popular there (about half of all passenger vehicles in Europe run on diesel). But if someone could produce a low-cost "clean" diesel engine, that could help provide a nice short-term means of reducing oil use here in the United States and mopping up air pollution over in Europe.