Abstract
The properties of CrO3–ZrO2 and Pt/CrO3–ZrO2 were studied by IR and ESR spectroscopy to elucidate the active sites in n-heptane isomerization and cumene cracking. Surface analyses showed the presence of cubic, monoclinic and tetragonal phases of ZrO2 with a BET specific surface area of about 150m2/g for both catalysts. 2,6-Lutidine adsorbed IR confirmed the presence of treble doublet bands at 1675+1660, 1650+1625 and 1640+1630cm−1 corresponding to Brønsted acid sites and quartet doublet bands at 1604+1580, 1595+1580, 1590+1580 and 1570+1560cm−1 corresponding to Lewis acid sites. The presence of Pt enhanced the activity of CrO3–ZrO2 in cumene hydrocracking, in which Pt facilitated the formation of protonic acid sites at 1675+1660 and 1650+1625cm−1 through a hydrogen spillover mechanism. The IR study verified that the Lewis acidic center at 1570+1560cm−1 was involved in the formation of protons by trapping electrons. Meanwhile, neither CrO3–ZrO2 nor Pt/CrO3–ZrO2 was active in n-heptane hydroisomerization.
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