Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

Li, Yuming; Fu, Shuting; Zhang, Qiyang; Liu, Hongyu; Wang, Yajun

doi:10.3390/catal12111371

Cited by 7 publications

(13 citation statements)

References 100 publications

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“…In contrast to [4] Ga sites, the most probable local environment of [5] Ga sites does not change notably with the number of ALD cycles, suggesting that [5] Ga sites interact less with the silica surface. The relative distributions of [4] Ga, [5] Ga and [6] Ga sites obtained from NMR fittings are consistent with the results of Ga K-edge X-ray absorption spectroscopy (XAS) and differential pair distribution function (dPDF) analysis. Surface acidity studies using pyridine (Py) as a probe molecule for Fourier transform infrared spectroscopy (Py-FTIR) and 15 N dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) reveal the presence of a high relative abundance of strong BAS (i.e., protonated Py) mostly on Ga1-SiO 2−500 , owing to the presence of gallosilicate Ga−μ 2 -OH−Si species in this material.…”

Section: ■ Introductionsupporting

confidence: 80%

“…190 ppm and 100 ppm (Table S2), assigned to [4] Ga and [5] Ga coordination environments, respectively. 58 The three-site simulation for Ga10-SiO 2−500 provides an additional component with δ̅ iso = 44 ppm, which is consistent with hexacoordinate [6] Ga sites. 12,59 However, it should be noted that the variance of the quadrupolar coupling distribution (σ Q ) is significantly Table 1.…”

Section: Chemistry Of Materialsmentioning

confidence: 66%

“…71 Ga NMR Parameters Retrieved from the Two-Component Simulations: Relative Fraction, Average Isotropic Chemical Shift δ̅ iso , and Full Width at Half Maximum of the Distribution of δ iso (Δδ iso ) and Variance of the Distribution of Quadrupolar Tensor Elements (σ Q ) a material [4] Ga δ̅ iso Δδ iso σ Q [5] Ga lower for this site than the ones found for [4] Ga and [5] Ga sites, indicating that the three-site simulation may be unreliable. Moreover, the relative fraction of the [6] Ga site is small (4%) and its impact on the fitting of the spectrum at 28.2 T is negligible. Therefore, these results show the presence of structurally disordered [4] Ga and [5] Ga sites and suggest the lack of detectable amounts of [6] Ga sites (ca.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

“…Moreover, the relative fraction of the [6] Ga site is small (4%) and its impact on the fitting of the spectrum at 28.2 T is negligible. Therefore, these results show the presence of structurally disordered [4] Ga and [5] Ga sites and suggest the lack of detectable amounts of [6] Ga sites (ca. <5%).…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

“…Fitting of high-field 71 Ga magic-angle spinning solid-state nuclear magnetic resonance (MAS NMR) data obtained at 20.0 T and 28.2 T shows that all three prepared Ga-SiO 2−500 materials contain mostly tetracoordinate Ga sites ( [4] Ga), in addition to pentacoordinate Ga sites ( [5] Ga), and only a minor amount of hexacoordinate Ga sites if present (ca. <5% [6] Ga). The most probable local environment of [4] Ga sites in Ga1-SiO 2−500 is [4] Ga(OGa) 1.2 (OSi) 2.8 and it evolves to [4] Ga(OGa) 2.5 (OSi) 1.5 and [4] Ga(OGa) 3.3 (OSi) 0.7 in Ga5-SiO 2−500 and Ga10-SiO 2−500 , respectively.…”

Section: ■ Introductionmentioning

confidence: 99%

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Nature of GaO_x Shells Grown on Silica by Atomic Layer Deposition

Chen,

Zimmerli,

Zubair

et al. 2023

Chem. Mater.

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Gallia-based shells with a thickness varying from a submonolayer to ca. 2.5 nm were prepared by atomic layer deposition (ALD) using trimethylgallium, ozone, and partially dehydroxylated silica, followed by calcination at 500 °C. Insight into the atomic-scale structure of these shells was obtained by high-field 71 Ga solid-state nuclear magnetic resonance (NMR) experiments and the modeling of X-ray differential pair distribution function data, complemented by Ga K-edge X-ray absorption spectroscopy and 29 Si dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) studies. When applying one ALD cycle, the grown submonolayer contains mostly tetracoordinate Ga sites with Si atoms in the second coordination sphere ( [4] Ga (Si) ) and, according to 15 N DNP SENS using pyridine as the probe molecule, both strong Lewis acid sites (LAS) and strong Brønsted acid sites (BAS), consistent with the formation of gallosilicate Ga–O–Si and Ga–μ 2 -OH–Si species. The shells obtained using five and ten ALD cycles display characteristics of amorphous gallia (GaO x ), i.e., an increased relative fraction of pentacoordinate sites ( [5] Ga (Ga) ), the presence of mild LAS, and a decreased relative abundance of strong BAS. The prepared Ga1-, Ga5-, and Ga10-SiO 2–500 materials catalyze the dehydrogenation of isobutane to isobutene, and their catalytic performance correlates with the relative abundance and strength of LAS and BAS, viz., Ga1-SiO 2–500 , a material with a higher relative fraction of strong LAS, is more active and stable compared to Ga5- and Ga10-SiO 2–500 . In contrast, related ALD-derived Al1-, Al5-, and Al10-SiO 2–500 materials do not catalyze the dehydrogenation of isobutane and this correlates with the lack of strong LAS in these materials that instead feature abundant strong BAS formed via the atomic-scale mixing of Al sites with silica, leading to Al–μ 2 -OH–Si sites. Our results suggest that [4] Ga (Si) sites provide strong Lewis acidity and drive the dehydrogenation activity, while the appearance of [5] Ga (Ga) sites with mild Lewis activity is associated with catalyst deactivation through coking. Overall, the atomic-level insights into the structure of the GaO x -based materials prepared in this work provide a guide to design active Ga-based catalysts by a rational tailoring of Lewis and Brønsted acidity (nature, strength, and abundance).

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