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Acid sites on Co-, Cu- and PtZSM-5 as well as on Pt,Co- and Pt,CuZSM-5 samples were investigated by means of pyridine adsorption monitored by IR spectroscopy. After reduction in hydrogen a significant amount of acidity was observed on each zeolite sample. The concentration of the Broensted acid centers was substantially diminished after treating these samples in NaCl solution. When NaBH4 was used as the reducing agent much less, in some cases a negligible amount of Broensted acid sites was detected, which did not significantly increase after reduction with hydrogen. Creation of the Lewis acid sites proved to be more complex indicated by several IR bands of coordinatively bound pyridine. As a result of this study, an applicable procedure is suggested for preparation of bimetallic zeolites of predetermined acidity. |
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