Googling I do shows some support for that, but it's not mainstream.

Precisely correct. All of the processes I've introduced are heavily-dependent on catalysts. Take a look at the water shift reaction, the steam reforming processes, and there are many other syngas processes that virtually all require catalysts. Iron is a catalyst that does actually get used in water shift and steam reforming. Cobalt is another common catalyst. Mant catalysts in these processes are industry secrets. I didn't want to introduce a new metal, so I just figured, "iron for simple catalyst recipes", "copper for advanced catalyst recipes."

Well... catalyst doesn't get used up in the reaction. It makes it a bit more difficult to mass process things if I also need to route iron/copper to them. But okay, that's what I thought.

I hear you, and I used to have it where the items were returned after use, but the vanilla game models catalysts as being "used" so I figured I would do the same. At least some of the items are set as catalysts in the prototype, but this doesn't appear to make any difference for inputs (for outputs it makes a difference related to modules). In the end it turned out to be a logistical nightmare to return and have to loop back in the iron outputs. So this is where we are. I'm open to arguments for other approaches.

What vanilla recipes use a catalyst?

I'd assume that the Oil Refineries and Chemical plants have catalysts available to them already, given the nature of what they do.

I may just edit my local version to give it back. At least to see how it does.

For example the use of iron to make sulfuric acid. I've interpreted that as using an iron catalyst. Do you think it's modeling something else?

No, it certainly looks like it's a "replacement" of the Vanadium oxide.

Well, natural gas and syngas are processed much more than sulfuric acid is produced, which is one reason why I asked. It takes a lot more routing of belts and such than a acid production does.

I'm going back through all my mods, doing any rebalances, whatever. I believe what I ended up doing for this is not to remove the catalyst or to bring make it an output as well as an input, but just to greatly reduce the number of catalyst plates needed. I think I reduced it by a factor of 2/5 as I also increased the amount of gas that gets processed. Hopefully that works better. Let mek now if you have any other balancing suggestions.

I believe ElAdamo is doing the right thing, originally, even as an applied chemist myself. Sometimes you just have to do the most illogical thing, for game-play reasons, and to make it more 'fun' as such. Real life can be quite 'boring' at times and especially in comparison plus not everyone using this mod would be a chemist either :)

Oops, I didn't realize I just necro'ed this thread. Apologies!

LOL no worries. I thought about this a lot and I feel that requiring a "catalyst plate" is the right gameplay balance. Methane production is borderline OP so that helps balance it.