Diphenylmethane-mediated transmethylation of methylbenzenes over H-zeolites.

Despite their vital roles in the catalytic cycle for toluene disproportionation, diphenylmethane (DPM)-type compounds have never been directly detected or proved to be true reaction intermediates from experimental techniques. In this report, we provide unprecedented insights into the DPM-mediated reaction mechanism, by demonstrating the build-up of DPM species inside the zeolite pores and following their decomposition. It can be stated that, despite their bulkiness, (di)methylated DPM species may indeed be formed at high concentrations in the ZSM-5 channels when toluene is reacted. The dimethyl-DPM species are unstable when present in the zeolite voids and decompose under a concomitant evolution of xylene at 200 degrees C.