Evaluating the per site activity of common mesoporous materials as supports for aminosilica catalysts for the aldol reaction and condensation

Brizes, Michael; Chen, Jee-Yee; Pineault, Hannah; Brunelli, Nicholas A.

doi:10.1016/j.apcata.2022.118997

Cited by 3 publications

(2 citation statements)

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“…Site quantification experiments have been applied to zeolite Beta, ,, other zeolite frameworks, and mesoporous catalysts such as amine-functionalized SBA-15. − For Sn-Beta, Harris et al used pyridine for titration experiments and complemented these results with FTIR using acetonitrile to identify open defect sites as the dominant sites for glucose isomerization, corroborating earlier findings. , Bates et al later expanded upon this work and determined that closed Sn sites were more active than open defect Sn sites for ethanol dehydration using similar techniques …”

Section: Introductionmentioning

confidence: 73%

“…Linear fits are performed for the data using MATLAB, as we have done previously, 65 with MATLAB determining the quantity of linear regimes as well as the slopes and ranges of each linear regime to best fit through all data points. From the MATLAB fits, the catalytic site distribution in Sn-Beta-200-10d using TEA is 23 ± 2% high activity, 44 ± 22% low activity, and the remainder are nonactive.…”

Section: Triethylaminementioning

confidence: 99%

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Counting Sites in Lewis Acid Zeolite Sn-Beta: Connecting Site Quantification Experiments and Spectroscopy To Investigate the Catalytic Activity for the Alcohol Ring Opening of Epoxides

2023

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Sn-Beta is a promising catalyst for numerous reactions involved in biomass upgrading and fine chemical production, but it is complex with multiple types of active sites. The activity for Sn-Beta can be calculated on a per-site basis using site quantification experiments that involve adding a Lewis basic probe molecule, but it is not clear which types of sites are being titrated. Our work connects site quantification experiments with spectroscopic measurements to explain differences in the catalytic activity of materials crystallized for different amounts of time. For alcohol ring opening of epoxides, experiments reveal that Sn-Beta crystallized for 10 days (Sn-Beta-200-10d) is more active than Sn-Beta crystallized for 40 days (Sn-Beta-200-40d). These materials are investigated using site quantification experiments with three probestriethylamine, pyridine, or 2,6-lutidineto reveal the different fractions and types of sites. As the probe:Sn ratio is increased, these experiments result in two distinct slopes, indicating two distinct activities: high and low activity. The difference in activity between Sn-Beta-200-10d and Sn-Beta-200-40d can be attributed to the reduced fraction of high-activity sites. Although the two slopes have typically been assigned to open defect Sn sites for high activity and closed Sn sites for low activity, 15N NMR measurements of materials dosed with 15N-labeled pyridine contradict this assignment. Indeed, at low concentrations, pyridine adsorbs on both open defect and closed Sn sites whereas the low activity corresponds to pyridine binding to SnOH groups in addition to closed Sn sites. Overall, the identification of appropriate site quantification experiment parameters and the combination of these titrations with NMR techniques allows for the establishment of a synthesis–structure–activity relationship that has the potential to improve the performance of Sn-Beta.

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