Solid‐acid Catalysis: Rearrangement and Isomerization

Sheldon, Roger A.; Bekkum, H. van

doi:10.1002/9783527612963.ch05

Cited by 1 publication

(1 citation statement)

References 144 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Q 3 / Q 4 ratios were high in S-1 (0.065), S-1-P (0.078), and S-2 (0.117), indicating that these three zeolites possess sufficient silanols to achieve high CHO conversion of 99.7, 99.8, and 50%, respectively. According to the OH stretching in FT-IR spectra, silanols could be classified into three categories, that is, terminal silanols (3740 cm –1 ), vicinal silanols (3690 cm –1 ), and silanol nests (3500 cm –1 ). , As shown in Figure b, S-1 and S-1-P possess abundant silanol nests, while silanols in S-2 are mainly in the form of terminal silanols with negligible silanol nests that lead to more side reactions to decrease the CPL selectivity to 50%. , …”

Section: Resultsmentioning

confidence: 99%

Modulating the Microenvironment of Silanols in Pure-Silicon Zeolites for Boosting Vapor-phase Beckmann Rearrangement of Cyclohexanone Oxime

Zhang,

Wang,

et al. 2023

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

Vapor-phase Beckmann rearrangement of cyclohexanone oxime (CHO) to ε-caprolactam (CPL) is still difficult to commercialize at the industrial scale due to its relatively low catalytic activity and poor lifetime. Herein, we synthesized a series of pure-silicon zeolites (including MFI, MEL, and −SVR) with three-dimensional 10-member-ring topolgies, diverse silanol status, and hierarchical porosity to investigate the synergistic effects of inner diffusivity and reactivity. S-1 zeolite of MFI-type topology with plentiful silanol nests exhibits a more preferable catalytic performance in terms of CHO conversion (99.7%) and CPL selectivity (89.7%), much higher than those of MEL-and −SVRtype zeolites mainly due to their diverse silanol distribution. With the construction of hierarchical porosity, S-1-P shows improved CPL selectivity of 94.1% owing to the enhanced diffusivity to shorten the retention time of the reactant and product molecules. The reaction mechanism and network have been further revealed by density functional theory (DFT) calculations and experimental designs, which indicate that silanol nests are major active sites due to their suitable interaction with CHO rather than terminal silanols. Particularly, the microenvironments of silanols can be modulated by alcohol solvents, ascribed to their different charge transfer and steric hindrance. Consequently, S-1-P shows superior CPL selectivity of 97.3% in ethonal solvents, which have higher adsorb energy of −0.627 eV with silanol nests than other alcohols. The present study not only provides a fundamental guide for the design of zeolite catalysts but also provides a reference for modulating the microenvironment of active sites according to the catalytic mechanism.

show abstract