Angels had a single opportunity to decide, for all eternity, whom they would serve. The devil and his cohorts began in heaven and knowing of its complete and total goodness, and after enjoying the beatific vision, they rebelled and were cast out of heaven. This was effectively their death after which there can be neither repentance, no redemption. They are irretrievably lost and no prayer can help them. This is a message for us - that even though we may have rejected God, we can repent - turn back - and He will welcome us just as the prodigals we are. From the catechism:
392 Scripture speaks of a sin of these angels.269 This “fall” consists in the free choice of these created spirits, who radically and irrevocably rejected God and his reign. We find a reflection of that rebellion in the tempter’s words to our first parents: "You will be like God."270 The devil “has sinned from the beginning”; he is “a liar and the father of lies”.271
393 It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels’ sin unforgivable. “There is no repentance for the angels after their fall, just as there is no repentance for men after death.”
414 Satan or the devil and the other demons are fallen angels who have freely refused to serve God and his plan. Their choice against God is definitive. They try to associate man in their revolt against God.