On the mutual interactions between noble metal crystallites and zeolitic supports and their impacts on catalysis

The mutual metal-support interactions were studied in mordenite zeolite modified with 0.5, 2 and 5 wt.% platinum by impregnation or ion-exchange method. Each modification method led to different catalysts from the point of view of acidity. These interactions were thoroughly investigated by XPS, CO and pyridine FTIR spectroscopy, NH₃-TPD and a model reaction (isomerization of n-butane). By XPS measurements and CO adsorption, it was observed that the Pt binding energy and the CO adsorption band increased with the acidity of the support. Simultaneously, a rearrangement on the strength of acid sites was recorded by pyridine-FTIR when the zeolites were modified by a metal function. Ultimately, such changes in acidity were translated into different catalytic performances, mostly by suppressing or favoring cracking reactions. The interatomic model was examined and extrapolated to cover the effects that the metal particles have upon the support acidity.