Influence of Bifunctional PtZn/SiO₂ and H-ZSM-5 Catalyst on the Rates and Selectivity of Propene Aromatization

Abstract

Previous studies on the conversion of olefins to aromatics with bifunctional Ga- or Zn-ZSM-5 catalysts have concluded that benzene, toluene, and xylenes (BTX) yields are significantly higher than for ZSM-5 alone. These results were attributed to the higher aromatic dehydrogenation rate of Ga or Zn. In this study, a highly active, bifunctional PtZn/SiO₂ (1.3 wt% Pt, 2.6 wt% Zn) with H-ZSM-5 (Si/Al = 40) catalyst is investigated for propene aromatization at 723 K and 823 K. At low to moderate propene conversions, in addition to BTX, small alkanes and olefins are produced. Many of these may also be converted to aromatics at higher propene conversion while others are not, for example, methane, ethane and propane. When compared at equivalent space velocity or propene conversion, the bifunctional catalyst has a much higher selectivity to aromatics than ZSM-5; however, when compared at equivalent conversion of all reactive intermediates, the bifunctional catalyst exhibits very similar BTX selectivity. At 723 K, for ZSM-5 the primary non-reactive by-products are propane and butane; while, for the bifunctional catalyst the major non-reactive product is propane. At 823 K, both ZSM-5 and the bifunctional catalyst convert propane and butane to aromatics increasing the aromatic yields, and the by-products are methane and ethane.