The hydroconversion of n-heptane over reduced and oxidized Pt/H-zeolite catalysts

The low-temperature (<443 K) hydroconversion of n-heptane was studied over Pt-containing HY, H-mordenite and H beta zeolites under atmospheric pressure. Activities and selectivities were found to be different for samples pre-oxidized in O-2 or pre-reduced in H-2 at 773 K. H-2-TPR results suggest that the high-silica content Pt,H-zeolites contain (Pt2O)(2+) species which are reduced to Pt degrees in two consecutive steps. When sample was evacuated, the OH-groups. The oxidation state of the Pt groups of the zeolite oxidized most of the Pt degrees atoms close to Pt atoms was characterized also by IR spectroscopy using CO as a probe. It was shown that in contact with C-7/H-2 mixture, most Pt species did not maintain its original oxidized (Pt2+) or reduced (Pt degrees) state. Data suggest that pre-oxidized and pre-reduced catalysts contain Pt(1+delta)+ and Ptdelta+ species, respectively, under reaction conditions. It is suggested that the reaction chain of n-C-7 conversion is initiated and terminated in a redox type process over Pt(1+delta)+ while in the presence of Ptdelta+ the conventional bifunctional mechanism may prevail.