Deacons can do only those blessings that are specifically designated for deacons.
There are 2 reasons deacons cannot do this blessing:
The more a blessing (or the thing being blessed) is attached to the public liturgy of the Church, the less a deacon can do any particular blessing. For example, the dedication of a new church building is very much attached to public liturgy, so a priest (sacerdos) is required; a bishop is preferred to a presbyter.
Only a priest can actually use a chalice and paten. Yes, a deacon has his part in using them, but in the context of Mass, where the priest is the celebrant. Since the chalice “belongs” (searching for a better word) to the order of priests, a priest is required to bless one.
The last part is not so much a reason as it is a direct answer: the ritual books clearly require a sacerdos (bishop or presbyter) to bless a chalice and/or paten.
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