Objection 1. It seems that angels can administer sacraments. Because a higher minister can do whatever the lower can; thus a priest can do whatever a deacon can: but not conversely. But angels are higher ministers in the hierarchical order than any men whatsoever, as Dionysius says (Coel. Hier. ix). Therefore, since men can be ministers of sacraments, it seems that much more can angels be.
Objection 2. Further, in heaven holy men are likened to the angels (Matthew 22:30). But some holy men, when in heaven, can be ministers of the sacraments; since the sacramental character is indelible, as stated above (Question 63, Article 5). Therefore it seems that angels too can be ministers of sacraments.
Objection 3. Further, as stated above (Question 8, Article 7), the devil is head of the wicked, and the wicked are his members. But sacraments can be administered by the wicked. Therefore it seems that they can be administered even by demons.
On the contrary, It is written (Hebrews 5:1): "Every high priest taken from among men, is ordained for men in the things that appertain to God." But angels whether good or bad are not taken from among men. Therefore they are not ordained ministers in the things that appertain to God, i.e. in the sacraments.
I answer that, As stated above (3; 62, 5), the whole power of the sacraments flows from Christ's Passion, which belongs to Him as man. And Him in their very nature men, not angels, resemble; indeed, in respect of His Passion, He is described as being "a little lower than the angels" (Hebrews 2:9). Consequently, it belongs to men, but not to angels, to dispense the sacraments and to take part in their administration.
But it must be observed that as God did not bind His power to the sacraments, so as to be unable to bestow the sacramental effect without conferring the sacrament; so neither did He bind His power to the ministers of the Church so as to be unable to give angels power to administer the sacraments. And since good angels are messengers of truth; if any sacramental rite were performed by good angels, it should be considered valid, because it ought to be evident that this is being done by the will of God: for instance, certain churches are said to have been consecrated by the ministry of the angels [See Acta S.S., September 29]. But if demons, who are "lying spirits," were to perform a sacramental rite, it should be pronounced as invalid.
Reply to Objection 1. What men do in a less perfect manner, i.e. by sensible sacraments, which are proportionate to their nature, angels also do, as ministers of a higher degree, in a more perfect manner, i.e. invisibly--by cleansing, enlightening, and perfecting.
Reply to Objection 2. The saints in heaven resemble the angels as to their share of glory, but not as to the conditions of their nature: and consequently not in regard to the sacraments.
Reply to Objection 3. Wicked men do not owe their power of conferring sacraments to their being members of the devil. Consequently, it does not follow that "a fortiori" the devil, their head, can do so.
Source: Summa Theologica (New Advent)