A Zr-Al-Beta zeolite with open Zr(<scp>iv</scp>) sites: an efficient bifunctional Lewis–Brønsted acid catalyst for a cascade reaction

Li, Gang; Gao, Lizhen; Sheng, Zhizheng; Zhan, Yueping; Zhang, Chaoyang; Ju, Jing; Zhang, Yahong; Tang, Yi

doi:10.1039/c9cy00853e

Cited by 28 publications

(23 citation statements)

References 53 publications

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“…X-ray photoelectron spectroscopy (XPS) can also distinguish isolated metal sites from the oxidic phase based on shifts of the electron binding energies although the exact positions of band maxima sometimes differ in the literature. ,− Furthermore, XPS can be used to follow the ion exchange of Zr “open” sites, as shown by Gao et al (see discussion in section ). Similarly, piperidine coordination results in a shift of the Ti 2p XPS spectral bands in comparison with the spectrum of free Ti sites …”

Section: Active Sitesmentioning

confidence: 99%

“…Beyond probe molecule band shifts, the strength of acid sites can also be assessed by thermal desorption and dosing experiments. NH 3 TPD is rarely used , to characterize tetravalent and pentavalent metal-substituted molecular sieves because their sites are relatively weaker than those of aluminosilicates for which this technique was originally developed. Accordingly, their measurements can be influenced by simultaneous desorption of physisorbed ammonia and ammonia from weak acid sites.…”

Section: Active Sitesmentioning

confidence: 99%

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Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

et al. 2022

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Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal–organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

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Section: Active Sitesmentioning

confidence: 99%

Section: Active Sitesmentioning

confidence: 99%

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

et al. 2022

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“…For comparison purposes, other Zr-containing silicates have also been prepared, including a nanosized Zr-Beta zeolite, a medium-pore Zr-MFI, and a mesoporous Zr-MCM-41 (see Experimental Section for details). − Despite these comparative materials presenting different Si/Zr molar ratios (see Table S1), UV–vis spectra reveals that most of the Zr species in these silicates have been incorporated as isolated species (see Figure S2).…”

Section: Resultsmentioning

confidence: 99%

In-Situ-Generated Active Hf-hydride in Zeolites for the Tandem N-Alkylation of Amines with Benzyl Alcohol

et al. 2021

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In this work, we have studied the catalytic activity of different silicates (MFI, MCM-41, and Beta) containing Lewis acid sites (including Sn, Ti, Zr, and Hf) for the tandem N-alkylation reaction of aniline with benzyl alcohol. The Hf- and Zr-Beta were the most active catalysts for this transformation, showing in both cases selectivities toward the corresponding N-benzylaniline higher than 97%. FTIR and DFT analyses confirm that the active sites in the Hf-Beta catalyst for this process are the open sites where one of the four Hf–O bonds is hydrolyzed. Moreover, the amount of these active species could be notoriously increased with previous thermal treatment of the Lewis acid zeolite with benzyl alcohol. Isotopically labeled experiments and theoretical mechanistic studies reveal that the N-alkylation reaction occurs through a hydrogen borrowing pathway, in which in situ Hf-hydride species were generated. Finally, the Hf-Beta zeolite was reused several times in the N-alkylation reaction without any appreciable deactivation detected. This catalytic system could be expanded to a variety of amines, including aliphatic and biomass-derived amines.

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“…The parent H-Beta shows shifts at −103.8, −109.1, and −112 ppm in the Q 4 range. The first band is due to (SiO) 3 Si(OAl), and the latter two correspond to Si(OSi) 4 . Furthermore, H-Beta also shows a Q 3 shift at −101.3 ppm, which is attributable to (SiO) 3 Si(OH) .…”

Section: Resultsmentioning

confidence: 99%

Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

Guo

et al. 2021

ACS Sustainable Chem. Eng.

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Ketonization reactions provide a feasible approach to remove oxygen and increase carbon chain length for conversion of biomass derived carboxylic acids. However, the reaction suffers from fast catalyst deactivation and low ketone selectivity. In this work, Lewis acidic heteroatom Ti-, Zr-, Ce-, and Sn-Beta zeolites were prepared using a twostep post-synthesis method and applied in vapor phase ketonization of propionic acid at 350 °C. Among these zeolites, Zr-Beta shows both the highest activity and selectivity. Characterizations indicate that Zr prefers the vacant tetrahedral site when the Zr content is < 7%, corresponding to the maximal fraction of vacant sites produced from dealumination of the parent H-Beta with a Si/Al ratio of 19. Extraframework Zr may also form at a Zr content ≥ 7%. The tetrahedrally coordinated framework Zr species (mainly in the structure of open sites) show Lewis acidic characteristic, and their density can be linearly correlated with the ketonization activity, indicating that these sites are active sites for ketonization. In contrast to rapid deactivation of H-Beta, the 7% Zr-Beta is stable for ketonization over 60 h, maintaining a conversion of ∼50% and a 3-pentanone selectivity > 96% at a space time of 2 h. The amount of coke deposition on Zr-Beta is about 1/3 of that on H-Beta, and the structure of Zr-Beta is preserved after 60 h of reaction. The results of this work indicate that Zr-Beta zeolite is a promising catalyst for ketonization with good stability and high selectivity toward ketone.

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A Zr-Al-Beta zeolite with open Zr(iv) sites: an efficient bifunctional Lewis–Brønsted acid catalyst for a cascade reaction

Abstract: A simple one-step strategy for the preparation of a bifunctional Zr-Al-Beta zeolite with external open Zr(iv) sites, showing high activity for the cascade reaction.

Cited by 28 publications

References 53 publications

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

In-Situ-Generated Active Hf-hydride in Zeolites for the Tandem N-Alkylation of Amines with Benzyl Alcohol

Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

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