The Order of Christian Funerals (OCF) says this:
[T]he practice of scattering cremated remains on the sea, from the air, or on the ground, or keeping cremated remains in the home of a relative or friend of the deceased are not the reverent disposition that the Church requires (OCF 416).
While cremated remains can be committed to the sea or to the ground in an urn, coffin, or other suitable container, the Church believes that the scattering of ashes is an irreverent treatment of the human body. In light of this, it would not seem appropriate to promise to scatter another person’s ashes, even those of a non-Catholic, and it may cause scandal to do so.
Cremation and Burial at Sea
Cremation in Catechesis and the Funeral Liturgy
Does the Church allow cremation?
The Church’s Norms for Cremation (Note: .pdf file)