Understanding the Role of External Brønsted Acidity on the Selective Ring-Opening of Perhydrophenanthrene over Ir/β Catalysts

Selective ring-opening (SRO) of bulky polycyclic cycloalkanes is a crucial process for producing high-quality fuels; however, its decisive catalytic descriptors remain poorly understood. Herein, the roles of different acid distributions on the SRO of perhydrophenanthrene were investigated by preparing a series of bifunctional Ir/β catalysts with different external Brønsted acid sites (BAS) densities. The results showed that the SRO of perhydrophenanthrene was governed by the density of externally accessible BAS, rather than by the total acidity or internal acid sites. The Ir/ExB catalyst enriched in external BAS exhibits markedly enhanced SRO activity and selectivity, whereas those with insufficient external BAS show negligible ring-opening performance. The SRO product yield exhibits a clear linear increase with the increase in external BAS density. These findings identify externally accessible BAS as a decisive descriptor for bulky polycyclic alkane SRO and provide guidance for the rational design of bifunctional Ir/β catalysts.