Correct sentence structure provides that these phrases should appear in clauses only if preceded by clauses also containing which and who. This rule, which also applies to but which and but who clauses, is a matter of parallel construction. Do not say "He is a man of intelligence, and who is an industrious worker." You can omit and or add a who clause: "He is a man who is intelligent and who is an industrious worker." Better still, eliminate the verbiage and say "The man is intelligent and industrious." The best way to improve "He showed much energy at first, but which soon vanished" is to omit but.
Dictionary of problem words and expressions. Harry Shaw. 1975.