Pt3Mn/SiO2 + ZSM-5 Bifunctional Catalyst for Ethane Dehydroaromatization

Ethane dehydroaromatization (EDA) is a potentially attractive process for converting ethane to valuable aromatics such as benzene, toluene, and xylene (BTX). In this study, a Pt3Mn/SiO2 + ZSM-5 bifunctional catalyst was used to investigate the effect of dehydrogenation and the Bronsted acid catalyst ratio, hydrogen partial pressure, and reaction temperature on the product distributions for EDA. Pt3Mn/SiO2 + ZSM-5 with a 1/1 weight ratio showed the highest ethane conversion rate and BTX formation rate. Ethylene is initially formed by dehydrogenation by the Pt3Mn catalyst, which undergoes secondary reactions on ZSM-5, forming C-3+ reaction intermediates. The latter form final products of CH4 and BTX. At conversions from 15 to 30%, the BTX selectivities are 82-90%. For all bifunctional catalysts, the ethane conversion significantly exceeds the ethane-ethylene equilibrium conversion due to reaction to secondary products. Low H-2 partial pressures did not significantly alter the product selectivity or conversion. However, higher H-2 partial pressures resulted in increased methane and decreased BTX selectivity. The excess hydrogen saturated the olefin intermediates to form alkanes, which produced methane by monomolecular cracking on ZSM-5. With an increasing reaction temperature from 550 degrees C to 650 degrees C, the benzene selectivity increased, while the highest BTX selectivity was obtained at 600 to 650 degrees C.