In situ IR investigation of n-hexane isomerization over Pt containing sulfated zirconia Original Research Article

Isomerization of n-hexane over Pt containing sulfated zirconia (Pt/SZ) and SZ was followed by in situ IR measurements. A constant conversion and high selectivity to iso-hexanes were only observed with Pt under hydrogen as carrier gas. In the IR spectra only subtle changes in comparison to the spectrum after activation of Pt/SZ were observed. In the active state of Pt/SZ neither the OH groups nor the sulfates are involved as adsorption sites for n-hexane. Therefore, Pt-proton adducts near sulfate groups and hydride ions connected to Lewis acidic sites are proposed as active sites on Pt/SZ. Over SZ and Pt/SZ using He as carrier gas the isomerization started with an oxidative dehydrogenation of n-hexane followed by a rapid deactivation. The latter reaction is characterized by water formation, by a band near 1670 cm−1 and a broad band in the range of 1540–1580 cm−1 assigned to oxidized carbon species and coke precursors or coke, respectively. The oxidized species are transformed during TOS into coke. Reactivation of the catalysts could only be achieved by oxidation in air.