AbstractPhosphorous‐doped boron nitride (PBN) was previously confirmed to be an effective metal‐free catalyst for the challenging topic of ethylbenzene direct dehydrogenation (DDH) to styrene. Here, the effect of mass transfer factors including the porosity and surface exposure degree of mesoporous‐PBN (m‐PBN) on its performance over DDH was investigated by control experiments. The central pore size of m‐PBN was closely dependent on the thiourea amount and heating rate. The m‐PBN with optimal pore size delivered a significantly improved styrene production rate of 21.47 mmolST g−1 h−1 and styrene selectivity over 98 %. Further, when m‐PBN was in‐situ grown on cordierite, the activity and stability of catalyst could be further enhanced to 27.08 mmolST g−1 h−1 for 50 h stable run, which presented a promising industrial application prospect. This paper justified that the mass transfer factors involved in two‐dimensional metal‐free catalysts were crucial for DDH of ethylbenzene.