Chemistry has a concept of a catalyst - Something that lowers the activation energy of a reaction thus increasing reaction rate. Why couldn't nuclear catalysts exist?
A chemical cataylst is a bit different because it doesn't require overcoming the coloumb barrier. If a nuclear catalyst existed, it would have to lower to almost no energy or even bypass the coloumb barrier for a D-D fusion reaction to occur at NTP. Do you know of any situations were the coloumb barrier has been altered?
They are supposedly very energy intensive to be produce, but it proves the concept of lowering the barrier.