Conversion of n-Pentane to aromatics: effect of surface modification by chemical liquid deposition and promoter over nano scale Ga/HZSM-5

Abstract

This work studied the effects of chemical liquid deposition, i.e., TEOS concentration and multicycle silylation on Ga/HZSM-5 on their catalytic performance in aromatization of n-pentane. The parent nano scale HZSM-5 zeolite catalysts were incorporated with Ga by impregnation method followed by silylation via chemical liquid deposition (CLD) using tetraethyl orthosilicate (TEOS) by varying concentrations and number of cycles. Moreover, the small amount of Pt, Zn, La and P was introduced by co-impregnation method to study the effect of promoter. The physical and chemical properties of catalysts were characterized by N2 physisorption, XRD, NH3-TPD, IPA-TPD, TPO, TPR, SEM and 27Al MAS NMR techniques. Catalytic activity was tested in a continuous flow fixed-bed reactor at 500 °C, atmospheric pressure, and WHSV of 5 h-1. The results indicated that the addition of Ga greatly improved the aromatics selectivity due to the presence of GaO+ species which acted as active site for dehydrogenation reaction. The TEOS concentration slightly increased the p-xylene selectivity while multicycle silylation significantly improved the p-xylene in mixed xylenes due to the formation of uniformity inert silica layer. The silylated catalyst exhibited the lower of n-pentane conversion resulting from its lower external acid sites. The co-impregnation with P promoted the aromatics selectivity because there was formation of SAPO interfaces, pentahedrally aluminium framework and medium acid sites.