Hey there. The catalyst comes from doing two timed plate puzzles within the raid. Uniquely, the game lets you complete the 'to equip' part of Necrochasm's catalyst before you even earn the catalyst. By that I mean catalysts usually have an unlock requirement after you earn it, like 'get 500 kills', before it lets you actually put the catalyst on the weapon. For Necrochasm you do not have to have earned the catalyst, to work on this step of the process. So when the triumph does pop, this triumph does not actually 'give' you the catalyst, no matter what it may look like. You still have to get it from the raid from the Crota's Minions timed puzzles, and once you do, you can insert it immediately.