Roles of niobium in the dehydrogenation of propane to propylene over a Pt/Nb-modified Al2O3 catalyst

Abstract

The application of Pt-based catalysts in propane dehydrogenation (PDH) is restricted by low propylene selectivity, metal sintering and carbon deposition. It has been reported that the performance of catalysts is strongly related to the electronic and geometric properties of the Pt particles and the acidity of the support. Herein, we report that a niobium-modified alumina supported platinum catalyst exhibits high propylene selectivity and superior stability. A high conversion of 28.8% and a high propylene selectivity above 96% are achieved over the Pt/Nb1Al2-O catalyst for propane dehydrogenation at 600 °C after 8 h in a fixed bed reactor. Consecutive dehydrogenation–regeneration operations showed that the stability of Pt/Nb1Al2-O was much higher than that of Pt/Al₂O₃. NH₃-TPD revealed that the strong acidity is decreased, while the medium acidity is increased after introducing niobium into Al₂O₃, which may be attributed to the formation of new acid sites, probably Lewis acid sites from niobium oxide species. CO-adsorbed FTIR spectroscopy, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) results revealed the enhancement of electron density and the decrease of dispersion of Pt particles after the introduction of Nb, which is beneficial for inhibiting the by-reactions (carbon formation and C–C bond cleavage).