Hi There,
This is a topic which has been covered here numerous times, and if you do a search you will find lots of info on it. Anyway, I will try to point you in the right direction:
-If you really want to know almost all there is about wood finishing, take a look at this book:
http://www.amazon.com/UNDERSTANDING-WOO ... 726&sr=8-2It is considered by many to be the "bible" on wood finishing...now to your question:
A catalyzed "anything" not just urethane, requires a "catalyst" before it is applied. This is like mixing epoxy with part A and part B, as an example. The catalyst will chemically react with the solution, you spray it, then it will dry. These have the advantage of usually being tougher (although people argue this) than a traditional finish, as well as the time required to cure is usually hours, as compared to days or even months with other finishes. You also need to use the "batch" you create, since if you store it, it will harden (unlike lacquer, where you can store in an air tight container until you use it, since it is an "evaporative" finish).
Now with this said, it is also a "hard" finish to apply, since if you make mistakes, it is usually not forgiving. Most are also TOXIC and VERY dangerous to your health! To use these finishes you would need the proper spray and PROTECTION equipment...
Anyway, I can write a book here, but I figured these will get you started....