Initial stages of propane activation over Zn/MFI catalyst studied by in situ NMR and IR spectroscopic techniques

The early stages of propane activation over Zn-modified H-MFI catalysts were studied by in situ ¹³C MAS NMR and IR spectroscopic techniques. Propane 2-¹³C, propane 1-¹³C, deuterated propane, and deuterated dihydrogen were used as labelled reactants. Both techniques pointed to the formation of zinc propyl species at the onset of propane conversion. Moreover, formation of ZnOH groups simultaneously to zinc propyl species was evidenced by IR spectroscopic techniques. The results point to the propane activation through dissociative adsorption over zinc oxide species, followed by propene evolution and recombinative desorption of dihydrogen. Propene further oligomerizes over acidic sites, while dihydrogen either evolves as a final product or participates in propane hydrogenolysis into ethane and methane. At low partial pressure of reactants, H₂ recombinative desorption and hydrogen evolution are favoured, whereas at high pressures, the hydrogenolysis route is preferable.