38 Effects of reducing and oxidising pre-treatments on the state of gallium in Ga/H-ZSM-5 propane aromatisation catalysts

Nowak, Izabela; Quartararo, Juliette; Derouane, Éric G.; Védrine, J.C.

doi:10.1016/s0167-2991(03)80195-7

Cited by 23 publications

(50 citation statements)

References 11 publications

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“…This is in agreement with the result of Védrine and colleagues [14] who showed experimentally the presence of OH groups bonded to the Ga atoms. In the SAPO S model, the formation of gallium dihydride is more exothermic (reaction (4)) than in the three ring system (reaction (12)), because in the three ring system the Ga atom is more bonded to and less exposed to the H 2 than in the small model.…”

Section: Three Ring Systemsupporting

confidence: 93%

“…Signal at 140 ppm was attributed to tetrahedral coordinate Ga 3+ species such as Ga(OH) 2 + coordinating to the Brønsted site. Védrine and colleagues [14] using various experimental techniques showed the presence of small GaO(OH) particles in Ga/H-ZSM-2 zeolites prepared by ion-exchange. The fact that repeated H 2 -reduction and O 2 -oxidation cycles increase the dispersion of gallium into the zeolite was explained considering that, in presence of H 2 at 873 K, the Ga 2 O 3 can be reduced to Ga 2 O that has a high vapour pressure.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical study of the Ga/SAPO-11 catalyst

Sierraalta

Guillén

López

et al. 2005

Journal of Molecular Catalysis A: Chemical

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Section: Three Ring Systemsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Theoretical study of the Ga/SAPO-11 catalyst

Sierraalta

Guillén

López

et al. 2005

Journal of Molecular Catalysis A: Chemical

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“…Therefore, the band at about 3630-3600 cm -1 may be attributed to Ga(OH)Si or Fe(OH)Si. The increased band intensity at 3660 cm -1 may be assigned to the formed extra-framework hydroxyl group, i.e., GaO(OH) and FeO(OH) [15,29,30]. Hence, after sublimation treatment, Ga(OH)Si and Fe(OH)Si are generated and SiOH(SiO) 3 is consumed.…”

Section: Aciditymentioning

confidence: 99%

“…In this reaction path, the formation of 3-picoline does not need a dehydrogenation step. Early investigations have reported that the extra-framework Ga 2 O 3 in ZSM-5 can be reduced to Ga + by H 2 , together with the consumption of B acid sites at 723 K, according to the following reaction [15,29]:…”

Section: Catalytic Performancementioning

confidence: 99%

“…Moreover, it has been reported that Ga + can promote the dehydrogenation process in propane aromatization [29,40]. Considering that H 2 was used as dilution gas in the reaction, that the catalyst was reduced at 723 K for 2 h before the reaction and that the reaction temperature was 723 K, it is reasonable to propose that part of the extra-framework Ga cations in the sample H-Silicalite-Ga can be reduced to Ga + under these conditions for the Chichibabin condensation.…”

Section: Catalytic Performancementioning

confidence: 99%

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Effect of Sublimation Treatment on the Catalytic Performance of MFI Catalysts in Pyridine and 3‐Picoline Synthesis

Jin

2011

Chem Eng & Technol

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Mordenite framework inverted (MFI)-structure catalysts with framework trivalent metal cations and extra-framework metal cations were prepared by the sublimation method to synthesize pyridine and picolines. The results show that the sublimation treatment of volatile metal halides, i.e., GaCl 3 and FeCl 3 , consumes the silanol groups of the parent sample. Most of the Ga cations are incorporated into the zeolite framework, which produces hydroxyl groups and dramatically enhances the proportion of Brönsted acid sites. At the same time, a large number of Fe cations exist in the extra-framework, causing an increase in the proportion of Lewis acid sites. The increased acid amount and strength effectively improve the activity and stability of the catalyst. Moreover, the generated stronger acid sites increase the selectivity of pyridine. The Ga cations of the modified zeolite can promote the dehydrogenation step for pyridine synthesis, which markedly increases the pyridine selectivity.

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Ethylene Dehydroaromatization over Ga‐ZSM‐5 Catalysts: Nature and Role of Gallium Speciation

et al. 2020

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Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here,w ee xamine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. We compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods.U sing ac ombination of state-of-the-art characterization, catalyst testing,and density functional theory calculations,weshow that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)-Ga(extra-framework) pairings, which can only be achieved in materials prepared by direct synthesis,are the most energetically favorable sites for reaction pathwaysl eading to aromatics.C alculated acid site exchange energies between extra-framework Ga at framework sites comprised of either Al or Ga reveal as ite-specific preference for stabilizing Lewis acids,w hich is qualitatively consistent with experimental measurements.T hese findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, whichc an have am arked impact on catalyst performance relative to conventional H-ZSM-5.

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38 Effects of reducing and oxidising pre-treatments on the state of gallium in Ga/H-ZSM-5 propane aromatisation catalysts

Cited by 23 publications

References 11 publications

Theoretical study of the Ga/SAPO-11 catalyst

Theoretical study of the Ga/SAPO-11 catalyst

Effect of Sublimation Treatment on the Catalytic Performance of MFI Catalysts in Pyridine and 3‐Picoline Synthesis

Ethylene Dehydroaromatization over Ga‐ZSM‐5 Catalysts: Nature and Role of Gallium Speciation

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