Two commercially available mordenites, obtained from Zeolyst (Si/Al = 10 at/at) and BASF (Si/Al = 8 at/at), were subjected to post-synthesis treatments. The impact of acid treatment, alkaline treatment (desilication) and a combination of both on porosity, crystallinity and catalysis were studied in detail. It was found that sequential acid and alkaline treatments were most effective to obtain mesoporous mordenite with external surface areas up to 250 m2 g-1. Electron tomography was used to visualize the mesoporosity of a series of sequential acid- and alkaline-treated mordenite samples. Mesopore formation started close to the external surface area and progressed toward the center of the crystallites for higher porosities. Liquid-phase alkylation of benzene with propylene to cumene was chosen to study the catalytic performance of the enhanced accessibility of various mordenite samples. The activity of the most porous mordenite was found to be close to that of a commercial zeolite beta, while selectivity toward the undesired n-propylbenzene was found to be significantly lower for mordenite (∼70 ppm) than for zeolite beta (∼175 ppm). These catalytic data indicate that the acid- plus alkaline-treated mordenite could be a viable catalyst in the cumene process.