Enhanced metathesis activity of low loading Re2O7/Al2O3 catalysts for propylene production by using aluminum nitrate as Al2O3 precursor

摘要

A series of alumina supported Re2O7 catalysts (4 wt% Re loading) were prepared by using aluminium nitrate (ANN) calcined at different temperatures (400, 550, and 750 degrees C) as the supports and impregnated with ammonium perrhenate solution. Despite their lower pore volume and smaller average pore size, the catalyst performances in the metathesis of ethylene and 2-pentene in terms of 2-pentene conversion and propylene selectivity of all the Re2O7/ANN were much improved as compared to the commercial gamma-Al2O3 supported one (Re2O7/Al-com) with the Re2O7/ANN-550 exhibited the best performances. Based on the in situ Infrared spectroscopy, the in situ Raman spectroscopy, and the in-situ IR spectroscopy of chemisorbed ammonia and thermodesorption results, the use of ANN as Al2O3 precursors provided higher acidic OH group and higher Lewis acid sites, which were necessary for the formation of the 2nd rhenium oxide active species especially for low Reloading. The higher Bronsted acidity on the Re2O7/Al-com, on the other hand, produced higher amount of coke and C5+ products. In addition, the acid strength of the Lewis acid sites appeared to be another important factor determining metathesis activity of the supported Re2O7 catalysts. (C) 2016 Elsevier B.V. All rights reserved.