Abstract <p>Tetramethyl bisphenol A (TMBPA) is a crucial industrial precursor synthesized through acid catalysis. Solid acid catalysts are preferred due to their ease of separation and environmental compatibility. However, the limited understanding of their catalytic mechanisms constrains their application. In this study, sulfonic acid (–SO₃H) and sulfhydryl groups (–SH) were employed to modify MCM-41 mesoporous molecular sieves to prepare solid acid catalysts. The solid acid catalysts were subjected to catalytic experimental evaluation and structural characterization. The results indicate that the dual-functional mesoporous catalysts exhibit exceptional catalytic activity, achieving a yield of 72.4%. A comprehensive catalytic pathway was proposed through theoretical calculations: The sulfonic acid group (–SO₃H) facilitates the protonation of acetone; the protonated acetone reacts with the sulfhydryl group (–SH) to form an isopropyl cation through dehydration; the isopropyl cation reacts with 2,6-dimethylphenol to form a 4-isopropyl-2,6-dimethylphenol cation; and this cation combines with another 2,6-dimethylphenol, releasing a hydrogen proton to produce TMBPA. The activation mechanism of the intermediate reveals that the sulfonic acid group (–SO₃H) induces a 0.011 electron transfer in the acetone molecule, thereby activating the molecule. The sulfhydryl group (–SH) activates the protonated acetone by transferring 0.359 electrons to the protonated species. 2,6-dimethylphenol undergoes a 0.183 electron transfer under the influence of the isopropyl cation, including 0.075 electrons at the solid–liquid interface and 0.108 electrons intramolecularly. The elucidation of the molecular-level catalytic pathway and the electronic-level activation mechanism provides a theoretical basis for the design of solid acid catalysts.</p> Graphical abstract <p></p>