ACIDIC AND TEXTURAL PROPERTIES OF H-ZSM-5 IMPREGNATED WITH GALLIUM, INDIUM OR THALLIUM

ZSM-5 samples with a silicon-to-aluminium atomic ratio of 25 were impr egnated with gallium, indium or thallium salts. The acidic and textura l properties of the samples were determined either before or after red uction. The acidity was investigated by infrared spectroscopy using py ridine (Py) as test molecule, titration with KOH or Py as well as ammo nia adsorption. Differences were revealed concerning the dispersion of impregnated species and the distribution of the acidic sites. The sit es containing ionic thallium were spectroscopically identified; the ot her sites were indirectly evidenced. Under our impregnation conditions , gallium species seem to enter inside the zeolite to a higher extent than was reported for similar samples. The contribution of indium to t he sample acidity was reduced because it is deposited as a distinct ph ase onto the external surface. An adsorption mechanism operating durin g impregnation was proposed on the basis of electrochemical measuremen ts; it was used to account for the acidity data. The textural properti es were interpreted in terms of the deposition of the impregnation spe cies near the pore mouth, hindering the entrance of the test molecules .