Abstract
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.
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