Your description of the experiment is a little far out there -- I also don't know of a household catalyst either. But, I don't know of a catalyst that slows down a reaction that is spontaneous and rapid, such a thing is usually called an inhibitor. I am also unaware how copper can be a catalyst, for this particular reaction, because it is already rapid, or even how it can be an inhibitor. So you may have to fill us in some more.