Well, refining petroleum is in itself not particularly clean, and ICEs are about as efficient as they're going to get. Electricity production, on the other hand, can get a lot cleaner in a variety of ways and not link you to a specific technology.

It's important to note that using hydrogen as a combustion fuel sounds like a good idea, as the immediate conclusion is that it just produces water, but if the oxygen supply is air, it ends up creating a variety of nitrous oxides, most of which are toxic at various levels.