Tunable activity of [Ga]HZSM-5 with H2 treatment: Ethane dehydrogenation

• Reduced Ga species is more active than the oxide species for ethane dehydrogenation.
• GaH2+ is the most active species and only available under stream of H2.
• Treating [Ga]HZSM-5 with H2 and/or H2O results in re-dispersion of Ga species.

Ethane dehydrogenation over [Ga]HZSM-5 catalyst were studied to probe activity of various gallium species (Ga2O3, GaO+, Ga+, and GaH2+) in a pulsed reactor. H2-TPR was used for characterizing the reducible Ga species. It was found that the activity of [Ga]HZSM-5 can be regulated by the H2 treatment. Among the various Ga species, the H2-incorporated species (i.e. GaH2+) displays the highest dehydrogenation activity (~ 55% conversion) under the H2 stream. However, this so-called GaH2+ can readily decompose in the absence of H2, presumably to Ga+ that give a lower ethane conversion (~ 30%). While the Ga oxide species, which may well be retained as isolated Ga2O3 and exchangeable GaO+, provide the lowest dehydrogenation activity (~ 25% conversion). The lower activity is observed with an increase in the Si/Al ratio of the host zeolite, suggesting that the active site is associated with the negative framework charge, presumably as a charge balancing cation (i.e. GaH2+, Ga+, GaO+). In addition, treatment with hydrogen and steam can readily disperse occluded Ga2O3 into exchangeable Ga+ and GaO+, respectively.