Effect of Cr2O3 loading on the properties and cracking activity of Pt/Cr2O3-ZrO2

Abstract

The effects of Cr2O3 loading ranging from 1 to 12 wt.% on the properties, structure and isopropylbenzene (IPB), 1,4-diisopropylbenzene (DIPB) and 1,3,5-triisopropylbenzene (TIPB) hydrocracking activities of Pt/Cr2O3-ZrO2 (Pt/CrZr) were studied. The properties of Pt/CrZr were characterized with XRD, BET, IR and UV–vis spectrometer. The acidity was determined by 2,6-lutidine adsorbed IR spectroscopy. The introduction of Cr2O3 on ZrO2 intensified continuously the tetragonal phase of ZrO2 and bulk crystalline Cr2O3, while the surface area and acidity passed through a maximum of Cr2O3 loading at 8 wt.%. The IR study confirmed the presence of Cr[dbnd]O stretching bands at 1035 and 1013 cm−1 on Pt/CrZr. No dioxo species involving the stretching modes of O[dbnd]Cr[dbnd]O existed. H2 and 2,6-lutidine showed different interactions with Pt/CrZr in which the band at 1013 cm−1 is more extensively affected with 2,6-lutidine adsorption for all Pt/CrZr and the band at 1035 cm−1 is more affected with H2 adsorption for Cr2O3 loading at ≤ 8 wt.%. While, at > 8 wt.% Cr2O3 loading, the H2 is more interacted with the band at 1013 cm−1. These results suggested that the absorbance bands at 1013 and 1035 cm−1 are assignable to the stretching of the Cr[dbnd]O which is connected to the other Cr through O and Cr[dbnd]O which is connected to cus Zr4+ through O, respectively. The catalyst with 8 wt.% loading performed with a maximum activity in IPB, DIPB and TIPB hydrocracking at 523 K which may be due to presence of Cr[dbnd]O band at 1035 cm−1 which extensively interacted with H2 to form protonic acid sites via a hydrogen spillover phenomenon. In fact, Cr2O3 loading at 8 wt.% possessed strong permanent Lewis acid sites which play an important role in the stabilization of an electron during the formation of protonic acid sites.