Formation of nitrogen from nitrates, nitrites and such is not easy indeed. I saw reports that mention it can be formed on platinum and gold, but not selectively. I never saw anything on producing sulfur from these oxide anions, but I can't say I know too much about it. In addition to the difficult reactions, the sulfur itself could be a problem though, as it might block the electrode when it is deposited.
Obviously these reactions need charge transfer, but the term CT catalyst is not common in this respect. Electrode materials that enhance electrochemical processes are usually referred to as electrocatalysts. I know it's just words, but using the common terms makes searching a bit easier.