Abstract Chemisorption of disilane on H-mordenite small port causes two types of structural modification: 1) homogeneous intracrystalline implantation of additional groups and/or 2) preferential pore entrance and external surface modification. The obtained type depends of the applied reaction conditions. The second modification process causes an efficient pore size reduction without loss of sorption capacity or acidity. The obtained substrates show a high resistance to a steaming treatment. The properties of these modified zeolites have been evaluated by chemisorption kinetics, gas adsorption experiments and FTIR-PAS spectroscopy.