Relating cumene hydrocracking activity to the acidic center of CrO3–ZrO2

CATEGORY: HYDROCRACKING
Journal of Molecular Catalysis A: Chemical 377 (2013) 162– 172
Relating cumene hydrocracking activity to the acidic center of CrO3–ZrO2
N.H.R. Annuar (a), A.A. Jalil (b), S. Triwahyono (a), (c), Z. Ramli (a)
a Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
b Institute of Hydrogen Economy, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
c Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
Abstract
The properties of CrO3–ZrO2and Pt/CrO3–ZrO2were studied by IR and ESR spectroscopy to elucidate theactive sites in n-heptane isomerization and cumene cracking. Surface analyses showed the presence ofcubic, monoclinic and tetragonal phases of ZrO2with a BET specific surface area of about 150 m2/g forboth catalysts. 2,6-Lutidine adsorbed IR confirmed the presence of treble doublet bands at 1675 + 1660,1650 + 1625 and 1640 + 1630 cm−1corresponding to Brønsted acid sites and quartet doublet bands at1604 + 1580, 1595 + 1580, 1590 + 1580 and 1570 + 1560 cm−1corresponding to Lewis acid sites. The pres-ence of Pt enhanced the activity of CrO3–ZrO2in cumene hydrocracking, in which Pt facilitated theformation of protonic acid sites at 1675 + 1660 and 1650 + 1625 cm−1through a hydrogen spillovermechanism. The IR study verified that the Lewis acidic center at 1570 + 1560 cm−1was involved in theformation of protons by trapping electrons. Meanwhile, neither CrO3–ZrO2nor Pt/CrO3–ZrO2was activein n-heptane hydroisomerization.
Introduction
Although previous studies have investigated the CrO3–ZrO2cat-alyst, there is currently a lack of published reports related to the acidity of CrO3–ZrO2 and Pt/CrO3–ZrO2. In the present study, authors report the acidic center–catalytic activity relationship of CrO3–ZrO2 type catalysts in n-heptane hydroisomerization and cumene hydro-cracking.
2,6-Lutidine was used as a basic probe molecule to evaluate the acidic properties of the catalysts. 2,6-Lutidine is usedwidely to evaluate the acidity of catalysts, particularly in the obser-vation of the relatively weak Brønsted acid sites and the acidiccenters of Lewis acid site types due to stronger basic propertythan pyridine. Hydrogen adsorbed IR and ESR spectroscopywere used to observe the participation of acidic centers in theformation of protons and electrons from molecular hydrogen at ele-vated temperature. Similarities and differences in the acidity andactivity of WO3–ZrO2, MoO3–ZrO2and CrO3–ZrO2catalysts are alsodiscussed.
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