Characterization and reactivity of Ga+ and GaO+ cations in zeolite ZSM-5

Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

“…[8][9][10][11][12][13] Quantumchemical calculations [13] showed that CÀH bond activation by reduced Ga/ZSM-5 proceeds over the Lewis acid-base pair formed by the Ga + ion and a zeolite-framework basic oxygen anion (Ga + ···ZO À ). The experimentally observed increase in activity of Ga + species in ZSM-5 upon oxidation at 473 K by nitrous oxide was ascribed to formation of gallyl (GaO + ) ions.…”

“…The experimentally observed increase in activity of Ga + species in ZSM-5 upon oxidation at 473 K by nitrous oxide was ascribed to formation of gallyl (GaO + ) ions. [8] Their higher reactivity is derived from more facile CÀ H bond cleavage catalyzed by the stronger Lewis acid-base pair formed by a Ga 3+ ion and the extraframework oxygen atom. The following elementary reaction steps [Eqs.…”

“…Earlier studies [6,10] [8] According to this reaction scheme, GaO + can be stabilized by addition of steam. Herein, we report experimental results showing that addition of steam indeed substantially increases the rate of alkane dehydrogenation over Ga/ZSM-5 and results in stable operation.…”

“…Catalyst performance in the presence of steam (0.3 kPa) was found to be stable over a period of at least 4 h. The very different product composition between Ga + /ZSM-5 in the absence of steam and HZSM-5 points to a change in the mechanism from protolytic hydrocarbon activation involving CÀH and CÀC bond cleavage for HZSM-5 to dominant C À H activation by the Lewis acidic Ga cations. [8] Addition of water to the feed strongly increases the activity. The main product remains propylene, although with increasing water content slightly increased amounts of methane and ethylene are formed.…”

Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

“…The water-induced enhancement in the rate of alkane activation by Ga/ZSM-5, as discussed herein, relates to transformation of these single Ga + centers to binuclear cationic Ga complexes involving a Ga 2 O 2 2+ core. Recent experimental [5][6][7][8] and computational [9][10][11][12][13] studies have contributed to our understanding of the mechanism of alkane activation by single Ga Lewis acid sites. As candidate active sites, various mononuclear Ga-containing cations (Ga…”