The problem isn't just a bunch of leaves, it's the pulp that gets generated by a layer of leaves that gets run over by heavy trains several times an hour. That pulp is particularly difficult to remove.

There are existing solutions for this, of course. For example, the Dutch railways deploy a mush of sand, potato fibers and iron particles on top of the mush to give trains the necessary grip when they brake while they take the caked on goop with them at the same time. This solution can be applied by separate trains running at relatively high speeds.

This approach, like the novel CO2 approach, has advantages and disadvantages, but it should be clear that "just attach a fan and a brush to the front" isn't going to cut it. You'd need a hell of a fan to blow sticky mush off the tracks at 60-65mph (average UK train speeds).