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

• Metathesis of ethylene and 2-pentene over low loading Re2O3/Al2O3 (4 wt%).
• Al(NO)3 precursor calcined at 550 °C provided higher acidic -OH than the Al-com.
• The 2nd rhenium oxide active species could be formed at relatively low Re loading.
• Amount and strength of the Lewis acid sites play important role in metathesis.
• Bronsted acidity was responsible for the formation of coke and C5+ products.

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 °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 γ-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 Re loading. 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.

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