Introducing sulphur surface groups in microporous carbons: A mechanistic study on carbide derived carbons

•Electrophilic aromatic substitution is predominant mechanism.•No mechanistic change upon variation of aromaticity of the porous carbon.•Spatial hindrance for electrophilic substitution within can be neglected.•Increasing sulfonic acid surface group density with increasing graphitization.•Highest catalytic solid acid performance for partly graphitized porous carbon.