if using this mod with https://mods.factorio.com/mod/DeadlockStackingForVanilla turn off the default setting to stack science packs in that mod's startup settings before enabling this mod.
stacking for vanilla uses the science pack subgroup category for stacking items and i assume it pulls this one since the added catalyst item is in the science pack subgroup. i'm new to modding factorio so i don't yet understand how most of the interactions within the lua files work but i guess the stacking mod is looking for a stacked version of catalyst and then throws a startup load error when it can't find it.

honestly it is fine with me since i was on the fence about the stacking science packs setting
either way i just wanted to leave a note here in case anyone else gets an error on startup like i did at first
cheers
-md

Thanks for your feedback.
I've had a quick look at this and I think you came up with the best solution.
If using this mod, disable science packs in the mod settings.

no worries
also thanks for this and the other mods (useful wood, recycle, etc) they are just what i was looking for in a mod list for my first modded space age session