The Chemical State of Gallium in Working Alkane Dehydrocyclodimerization Catalysts. In situ Gallium K-Edge X-Ray Absorption Spectroscopy

Synchrotron X-Ray Fluorescence Microscopy of Gallium in Bladder Tissue following Gallium Maltolate Administration during Urinary Tract Infection

“…The spectra collected in this study, particularly those from mice B and C, are of sufficient quality to suggest that the determination of gallium species is possible in these samples. The edge energy inflection point, approximately 7 eV above the tabulated electron binding energy for the gallium K-edge, is similar to previously reported observations for Ga 2 O 3 and for Ga(NO 3 ) 3 (34,35). While these spectroscopy results are preliminary, they demonstrate that near-edge X-ray absorption spectroscopy is possible and that extended X-ray absorption fine-structure spectroscopy (EXAFS) may be possible at the gallium K-edge in tissue samples despite the low gallium concentrations observed during treatment.…”

In situ Ga K edge XANES study of the activation of Ga/ZSM-5 prepared by chemical vapor deposition of trimethylgallium

“…Meitzner et al [10] reported the formation of reduced Ga species on Ga/HZSM-5 prepared by impregnation of gallium nitrate followed by air calcination upon reduction at 780 K. Clearly, the gallium alkyl precursor can be reduced at a considerably lower temperature than the gallium oxide one. Figure 6 presents XANES spectra of the material after reduction at 773 K and subsequent oxidative and reductive treatments at 773 K. One observes that oxidation at 773 K leads to dramatic changes in the XANES region.…”

“…Nevertheless, we will also address the oxidation of the zeoliteoccluded gallium alkyl species. A previous Ga K edge XAS study [10] indicated that the oxidation state of the reduced Ga species changes upon cooling indicating that in situ studies at relatively high temperatures are a prerequisite. Therefore, we studied the catalytic materials by XANES under conditions relevant to catalysis.…”

“…The reaction mechanism is thought to consist of a complex scheme involving dehydrogenation, oligomerization and ring-closure steps. Despite considerable research efforts in the area of Ga-containing zeolites [3][4][5][6][7][8][9][10][11], the exact role of gallium in this mechanism has not been totally elucidated yet, with proposals for its role as dehydrogenation function in a pure bifunctional [3][4][5][6] or concerted mechanism [7] and as a promoter to recombinative hydrogen removal during alkane dehydrogenation on Brønsted acid sites [8][9][10][11] receiving most attention. The structure of the active intrazeolite Ga species and their reactivity in oxidative and reductive conditions has not been fully resolved yet, owing to the wide variety of possible structures including bulk Ga 2 O 3 aggregates on the external zeolite surface, small gallium oxide aggregates occluded in the zeolite micropore space, reduced Ga species such as Ga 2 O and cationic Ga species in oxidized or reduced form.…”

A DFT Study of Hydrogen–deuterium Exchange over Oxidized and Reduced Gallium Species in Ga/HZSM-5 Zeolite

“…This is commercially applied in the Cyclar process [2,3]. It is generally believed that gallium acts as a promoter to recombinative hydrogen removal during alkane dehydrogenation [1,[4][5][6][7][8][9]. The nature of the active gallium species are still under debate and cationic species such as Ga + [8], GaH 2 + and GaO + replacing the Brønsted acid protons to compensate the framework charge [10] as well as small neutral gallium oxide clusters are considered.…”