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

just adding to this as another compat note after testing some more mods together.
age of production and maraxsis both add new alternate science pack recipes with different names and regular results but it doesn't look like either mod sets a main product for these new packs which i am guessing prevents catalyst from loading since from what i can tell it needs the name or main product to add to these recipes. so i added the main product for each one of these alternate pack recipes on my end in a data-updates file and it worked for me.
--
(age of production - i did this for all the flavours of specialized science pack recipes added)

if mods["Age-of-Production"] and mods["quirkycat_catalyst"] then
if data.raw.recipe["aop-hydraulics-specialized-cryogenic-science-pack"] then
data.raw.recipe["aop-hydraulics-specialized-cryogenic-science-pack"].main_product = "cryogenic-science-pack"
end
--
(and then the same thing for each deep sea pack recipes added by maraxsis)

if mods["maraxsis"] and mods["quirkycat_catalyst"] then
if data.raw.recipe["maraxsis-deepsea-research-automation-science-pack"] then
data.raw.recipe["maraxsis-deepsea-research-automation-science-pack"].main_product = "automation-science-pack"
end
--
i'm sure there is a less clunky and/or more elegant way of doing it but i'm still pretty green.
i have learned some things in the past month - at least enough to successfully patch things together on my end most of the time (with a lot of trial and error but that is the nature of modding)

You could publish a compatibility mod with your fixes...

aye will do - been working on a "patch" mod for science related stuff in my load order so i'll include this fix with that once i really get rolling with it