Does the catalyst have an expiry date? If so, after how long does it stop catalysing properly?Do you recommend keeping it in the fridge so that it lasts longer? Or does that make things worse?

The ink catalyst doesn’t have an expiry date.

As is also the case for inks, catalysts shouldn’t be kept in extreme temperatures, therefore the fridge isn’t the place to keep it. It should be stored in a cool, dry place and away from any direct light or heat sources.