"spend catalyst" means nothing. The spend portion says that it was used and not new, so not informative. Catalysts are tools used to make chemical reactions faster/producing less waste/cheaper. It can be as simple as acid (they are not dangerous is diluted), iron, amino acids or literally anything else. Depending on the process they can also have residue of whatever they made in the plant or the raw materials (because it is spend).
So unless you have more information there's not much you can do.