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

Liquid metals for boosting stability of zeolite catalysts in the conversion of methanol to hydrocarbons

Methanol-to-hydrocarbons (MTH) process has been considered one of the most practical approaches for producing value-added products from methanol. However, the commonly used zeolite catalysts suffer from rapid deactivation due to coke deposition and require regular regeneration treatments. We demonstrate that low-melting-point metals, such as Ga, can effectively promote more stable methanol conversion in the MTH process by slowing coke deposition and facilitating the desorption of carbonaceous species from the zeolite. The ZSM-5 zeolite physically mixed with liquid gallium exhibited an enhanced lifetime in the MTH reaction, which increased by a factor of up to ~14 as compared to the parent ZSM-5. These results suggest an alternative route to the design and preparation of deactivation-resistant zeolite catalysts