system
Given the following post, respond as if you're commenting on Reddit:
human
Why are iron (Fe) and cobalt (Co) good catalysts for creating hydrocarbon chains?

I've been reading on slurry bed reactors, and i know that cobalt is more power efficient (less heat required) than iron in reactors, but what i don't understand is the mechanism which Co or Fe allow Carbon Monoxide (CO) and Hydrogen (H) to do this:

>(2n+1) H2  +  n CO  → Cn H(2n+2)  +  n H2O

I have no chemistry background, so be gentle!

Oh, and if the explanation explains where "coke" comes from in this reaction, that would be excellent, too.

Thank you!
gpt
There are at least three possible mechanisms, and which one predominates may depend on temperature, pressure and catalyst. As to why these metals (and nickel and ruthenuim) are good, other metals would give either different, less useful products or nothing at all, or not be stable under the conditions. All these metals absorb CO and H2 well on to their surface, which is a key prerequisite to getting them to react. The precise steps after these two molecules absorb is still being studied.