Flame Synthesis of Zr/ZSM-5 Catalysts with Tunable Acidity for the Oxidative Dehydrogenation of Propane to Propene

Tuning the surface acidity of ZSM-5 catalyst is essential to achieve desired propene selectivity and yield. Here several ratios of Zr were utilized to modify ZSM-5 via flame spray pyrolysis technique coupled with a pulse spray evaporation system. The interaction between Zr and ZSM-5 in the flame influenced the physicochemical and acidity properties of the Zr/ZSM-5. The increasing Zr ratio in ZSM-5 shows coated layers of irregular nano-sized Zr with an increase in crystallite sizes due to the synergetic effect between Zr and ZSM-5. The surface chemical analysis revealed increased lattice oxygen on the Zr modified ZSM-5 (1:4) sample compared to other catalysts. The acidity analysis revealed the Lewis and Bronsted acid distribution in the weak and medium acid sites on the catalyst surface. However, the increase in Zr loading decreased the concentration of Bronsted acid sites and tuned the catalyst surface to more Lewis acidity, promoting propene selectivity and hindering the over-oxidation of propene. The modified ZSM-5 catalysts were examined in a fixed bed reactor within 300-700 degrees C at a gas hourly space velocity (GHSV) of 6000 mL center dot g(catalysts)-1 center dot h-1 for the oxidative dehydrogenation of propane (ODHP) to propene. Among the catalysts, Zr/ZSM-5 (1:4) exhibited the best propene yield, with 57.19% propane conversion and 75.54% selectivity to propene and the highest stability. This work provides a promising strategy for tuning the surface acidity of ZSM-5 with Zr for ODHP applications.