Silver Surfer is simply outright more powerful than Superman in every way apart from physical strength – but that makes no difference because he is too durable to be hurt by Superman’s own physical attacks, given that he can casually hang out in a black hole (or he could just go intangible to avoid them) and he has a multitude of other powers that he could use to defeat the Kryptonian hero.
The Silver Surfer is many times faster than light, whereas Superman’s speed tends to cap off at around lightspeed, so the Surfer can win the fight in a straight up one-on-one battle before Superman has processed a thought.
He could do so, for example, by turning Superman in to a teapot using transmutation – something that Superman has absolutely no defence against – or he could emit massive amounts of Kryptonite radiation, given that he has a proven ability to do such things with varying types of radiation.
If he was feeling eccentric, he could transmute Clark’s heart into a block of Kryptonite – and I remind you, this would all happen before Superman could process a thought, thanks to Surfer’s incalculably superior speed. Martian Would give Ss a better fight