Benevolent, beneficent are closely related rather than strictly synonymous terms.
Benevolent, which applies primarily to persons, means kindly in feelings and disposed to be generous or charitable, thereby emphasizing the will to do good, while beneficent, which applies to persons and things, means doing or effecting good, thereby emphasizing the fact of doing good.
Consequently benevolent is not only applied to a person, a group, or an institution, but to matters (as looks, attitudes, intentions, manners, and tones) that suggest a kindly disposition or a wish to help.
Benevolent may sometimes take on a new connotation either seriously or ironically and suggest the attitude of a person on the outside who is little more than a well-wisher.
Beneficent heightens the implication of doing good. It is therefore preferred when the emphasis is upon accomplishment rather than upon intention.
Unlike benevolent, beneficent may be used without any hint of volition and is then applicable to the benefits produced by things.