Brønsted/Lewis Acid Sites Synergy in H-MCM-22 Zeolite Studied by 1H and 27Al DQ-MAS NMR Spectroscopy

Yu, Zhengkun; Wang, Qiang; Chen, Lei; Deng, Feng

doi:10.1016/s1872-2067(10)60287-2

Cited by 27 publications

(15 citation statements)

References 51 publications

(70 reference statements)

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“…38 From the simulated 27 Al MQ MAS NMR spectrum, it is evident that 8 T sites can be divided into 3 groups: the T1, T3, T4, T5, T7 and T8 sites belong to the signal at δ 56 ppm, while the T2 and T6 sites correspond to the signals at δ 61 and δ 49 ppm, respectively. 32,39 In accordance with the conclusion, three peaks at δ = (49, 53), (56, 60) and (61, 66) ppm of the calcined MCM-22 can be clearly distinguished in the 2D MQ MAS NMR spectrum of Fig. 8(a).…”

Section: Catalysis Science and Technology Papersupporting

confidence: 87%

“…30 The additional peak at around 0 ppm −1 is due to the octahedral extraframework aluminum (Al ef ), which comes from the calcination process. 31,32 The signal corresponding to the Al f species shows a major resonance at 57.8 ppm along with shoulders at ca. 50.5 and 63 ppm.…”

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

“…33,34 Based on the hexagonal P6/mmm structure, the structure of MCM-22 has the 8 crystallographically distinct T (Si, Al) positions (as shown in Scheme 1), their quantity ratio is T1 : T2 : T3 : T4 : T5 : T6 : T7 : T8 = 1 : 3 : 3 : 1 : 1 : 3 : 3 : 3, which have been confirmed by 27 Al MQ MAS NMR and quantum chemical calculations. 32,[35][36][37] These eight unequivalent T(Si, Al) positions are associated with bridging hydroxyl groups (SiOHAl) as the Brønsted acid site. 38 From the simulated 27 Al MQ MAS NMR spectrum, it is evident that 8 T sites can be divided into 3 groups: the T1, T3, T4, T5, T7 and T8 sites belong to the signal at δ 56 ppm, while the T2 and T6 sites correspond to the signals at δ 61 and δ 49 ppm, respectively.…”

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

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The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22

Jin

Huang

Cheng

et al. 2015

Catal. Sci. Technol.

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A novel mesopore silica-aluminium material, i.e., Si/Ti-MCM-36 derivatives were prepared with Si/Ti mixed oxide as a pillar. The influences of acidity from Al species and the coordination state of Ti species on the catalytic cylcohexene epoxidation with t-butylhydroperoxide (TBHP) as the oxidant were investigated. The mesoporous structures were confirmed by XRD and N 2 ads/desorption experiment. The acidity and surface polarity were characterized by NH 3 -TPD, 27 Al 2D MQ MAS NMR and 29 Si MAS NMR. The Ti coordination state was identified with UV-Vis spectra. By using 27 Al 2D MQ MAS NMR technique, the Al species from the different eight crystallographically T (Si, Al) positions of MWW zeolite were identified, which are associated with bridging hydroxyl groups such as the Brønsted acid site. It was found that the Si/Ti-MCM-36 samples, whether with tetrahedrally (T d ) or octahedrally (O h ) coordinated state Ti species, are all inactive for the cyclohexene epoxidation. A further acid treatment of the Si/Ti-MCM-36 samples can greatly expel Al species from the MWW structure, which largely decrease the acidity and transfer the acid-catalyzed decomposition of t-butylhydroperoxide to Ti catalyzed cyclohexene epoxidation. It shows that not only the amount of Al species but also their framework crystallographic positions have a great influence on the epoxidation activity. Furthermore, the grafting of the tetra-isopropoxide on the acid treated Si/Ti-MCM-36 can increase its hydrophobicity and epoxidation activity. Moreover, the T d TiO 4 in the units has been confirmed to be the most active site for the epoxidation reaction.

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Section: Catalysis Science and Technology Papersupporting

confidence: 87%

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

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The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22

Jin

Huang

Cheng

et al. 2015

Catal. Sci. Technol.

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“…Accordingly, the 1 H-1 H distance between a Brønsted acidic proton and an extra-framework AlOH species in the supercage was determined to be 0.43 nm, whereas the average distance between two nearby Brønsted acidic protons in the supercages was measured to be 0.5 nm. The 1 H-1 H DQ MAS NMR spectroscopy was also employed to investigate the spatial proximity of acid sites in H-Y zeolites modified with different calcination, steaming, and acid-leaching treatments, and highly siliceous zeolites, such as H-ZSM-5, H-mordenite, and H-MCM-22 39,40 . All these findings provide insights into the roles of Lewis acid and its synergy with the Brønsted acid in zeolite-mediated hydrocarbon reactions.…”

Section: Introductionmentioning

confidence: 99%

“…With the assistance of DFT theoretical calculation, a new dealumination mechanism was proposed and three types of EFAL species, in close proximity to framework aluminum were identified in dealuminated HY zeolites. The spatial proximities of Brønsted and Lewis acid sites in the highly siliceous zeolites, such as H-MOR, H-ZSM-5, and MCM-22 zeolites, were also investigated by the 2D 27 Al- 27 Al DQ MAS experiments 39,40 . It was found that the Brønsted/Lewis acid synergy was present in these highly siliceous zeolites as well.…”

Section: Introductionmentioning

confidence: 99%

Solid-State NMR Characterization of the Structure and Catalytic Reaction Mechanism of Solid Acid Catalysts

Li¹,

Li²,

Zheng³

et al. 2017

Acta Physico-Chimica Sinica

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Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.

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Identifying the Role of Brønsted and Lewis Acid Sites in the Diels‐Alder Cycloaddition of 2,5‐DMF and Ethylene

Coumans,

Mezari,

Hensen

2023

ChemCatChem

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The role of Lewis and Brønsted acid sites in the Diels‐Alder cycloaddition (DAC) of ethylene to 2,5‐dimethylfuran (2,5‐DMF) to p‐xylene was investigated. Amorphous silica catalysts containing Al3+ (ASA), Ga3+ (ASG), and In3+ (ASI) were prepared via homogeneous deposition‐precipitation. Silica modified with Zr4+ (ASZ) was prepared by impregnation. Their acidic properties were characterized by various IR and NMR spectroscopic techniques. Measurements using pyridine as a probe molecule highlighted the presence of mostly Lewis acid sites (LAS) in all materials. Using CO as a probe, in contrast, demonstrated the existence of Brønsted acid sites (BAS) in ASA and ASG, which were nearly absent in ASI and ASZ. Differences in basic strength can explain the contrast in results observed between the two probe molecules. The highest p‐xylene yield (~20 %) in the DAC reaction, could be achieved with ASA and ASG. The lack of BAS in ASI and ASZ resulted in inferior performance in the DAC, with p‐xylene yields below 5 %. These results indicate the importance of BAS for the DAC reaction. Several other heterogeneous and homogeneous catalysts were explored for the DAC reaction to show the generality of our conclusion that BAS play a critical role in obtaining p‐xylene from 2,5‐DMF and ethylene.

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Brønsted/Lewis Acid Sites Synergy in H-MCM-22 Zeolite Studied by 1H and 27Al DQ-MAS NMR Spectroscopy

Cited by 27 publications

References 51 publications

The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22

The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22

Solid-State NMR Characterization of the Structure and Catalytic Reaction Mechanism of Solid Acid Catalysts

Identifying the Role of Brønsted and Lewis Acid Sites in the Diels‐Alder Cycloaddition of 2,5‐DMF and Ethylene

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