Insights into the efficiency of hydrogen peroxide utilization over titanosilicate/H2O2 systems

Yu, Yunkai; Tang, Zijie; Wang, Jia; Wang, Rui; Chen, Zhe; Liu, Haoxin; Shen, Kaixu; Huang, Xingliang; Liu, Yueming; He, Min

doi:10.1016/j.jcat.2019.09.045

Cited by 42 publications

(35 citation statements)

References 121 publications

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“…In order to limit the oxidant decomposition and thus improve the H 2 O 2 utilization efficiency, several solutions have been proposed, such as the use of low H 2 O 2 concentrations, the slow addition of the oxidant, the reduction of the local H 2 O 2 concentration around the Ti centers via surface hydrophobization (see below), or the use of additives that stabilize the Ti−OOH intermediate ( e. g . phosphate monobasic anions) [116,117] …”

Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

2021

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Epoxidation reactions are tremendously important for modern chemistry, as they lead to series of highly useful bulk and fine chemicals, monomers, and intermediates for organic synthesis. Progress in epoxidation processes goes hand in hand with the advancement made in catalysis science. In this context, heterogeneous catalysts, and particularly Ti‐based formulations, are playing a central role and have seen tremendous developments over the past two decades, leveraging on advanced materials science. The aim of this review is to illustrate the various strategies of titanosilicate catalysts preparation that can lead to more versatile, more performant, and greener epoxidation processes. We successively cover (i) supported catalysts, obtained by the grafting of Ti species onto preformed silica supports, (ii) microporous crystalline titanosilicates (zeolites), and (iii) amorphous titanosilicates obtained by sol‐gel chemistry. For each category, with an emphasis on catalyst preparation, the challenges that have to be tackled to boost catalyst performance are highlighted. From that point, we present a critical review of the different approaches that have been proposed in the primary literature to tailor the properties that govern catalysts performance (activity, selectivity, stability, ease of handling). This is done by better controlling the nature of the active surface species, adapting particles size and shape, optimizing texture, modifying surface chemistry, etc. These lines of attack encompass molecular approaches for the grafting of well‐defined species, top‐down and bottom‐up synthesis of hierarchically porous zeolites, advanced sol‐gel routes potentially performed in non‐conventional media or coupled with original processing, preparation of self‐standing monoliths, etc. Future research directions are discussed with emphasis on the application scope of new catalytic materials and possible approaches to increase catalyst performance.

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Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

2021

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“…However, this would cause a thermal accumulation effect, resulting in the decomposition of unstable samples. Particularly, the catalytically relevant Ti–OOH species usually suffers from thermal-induced decomposition, especially in the vapor-phase propylene epoxidation reaction. , In light of this, Raman measurements were performed here at continuous exposure times to detect the stability of Ti–OOH species in bio-TS-1. Noticeably, in order to balance the test convenience and accuracy, urea hydrogen peroxide was used here to simulate the in situ -generated peroxide from a H 2 /O 2 atmosphere to yield a similar Ti–OOH species for testing …”

Section: Resultsmentioning

confidence: 99%

“…This contributes to hinder the useless decomposition of HOOH intermediates to yield H 2 O and the following hydrolysis isomerization of PO, thus increasing the H 2 efficiency and PO selectivity of the bio-TS-1 support. In the latter case, the resulting electrophilic biomediated Ti–OOH species are more reactive to epoxidize the double-bonded carbon, in favor of the improvement of conversion and selectivity consequently . Because most of the coke results from the aggregation of byproducts, such an increase in selectivity would endow a better coke-resistant ability for the bio-TS-1-based catalyst .…”

Section: Resultsmentioning

confidence: 99%

“…Titanium silicalite-1 (TS-1) was first synthesized by Enichem’s group using the classical hydrothermal method in 1983, with Ti atom tetrahedral substitution of Si in the MFI lattice to serve as framework Ti . It allows the operation of olefin epoxidation with water as a byproduct showing huge atom economy, which is regarded as a milestone in the sustainable heterogeneous catalysis field. − Such a catalytic process generally exploits a hydrogen peroxide reagent as a green oxidant, which includes either the ready-made H 2 O 2 solution , or the in situ -generated HOOH species from H 2 /O 2 . , The reaction mechanism for the TS-1/hydrogen peroxide system has been explored for decades and could be described as to that the framework Ti first activates the hydrogen peroxide reagent and then transmits the resulting titanium–hydroperoxide species (Ti–OOH) to react with olefins. ,, In such cases, the coordination-unsaturated framework Ti chelates with the electron-rich hydrogen peroxide reagent and thereby decreases the electron density of its dioxygen moiety, which overall makes Ti–OOH more electrophilic to epoxidize the double bonds of olefins (CC). − That is to say, the framework Ti in TS-1 actually acts as a Lewis acidic catalyst, of which the strength determines its catalytic performances. ,,, Thus, it is of great scientific importance to improve the Lewis acidity of TS-1 zeolite, namely, the acidity character of framework Ti.…”

Section: Introductionmentioning

confidence: 99%

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Biophenol-Mediated Solvent-Free Synthesis of Titanium Silicalite-1 to Improve the Acidity Character of Framework Ti toward Catalysis Application

Wang

Zhai

et al. 2020

ACS Sustainable Chem. Eng.

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Although titanium silicalite-1 (TS-1) with enhanced Lewis acidity can show significant catalytic functionality, the effective and green synthesis of such a TS-1 zeolite still remains a challenge. In this work, a biophenol-mediated solvent-free strategy is adopted to synthesize bio-TS-1 with an improvement of acidity character. Systematic characterizations are devoted to inspect the structural and acidic properties of the as-prepared bio-TS-1. Furthermore, density functional theory simulations are carried out to reveal the underlying mechanism for such an improvement of acidity. It is found that biophenol serving as a mediating agent realizes a homogeneous crystallization process for bio-TS-1, which fundamentally favors titanium substitution of framework sites, especially those with unique acidity. This improvement of acidity boosts the intrinsic catalytic reactivity of Ti−OOH species, further increasing the performances toward propylene epoxidation. The presented strategy together with mechanistic results clarifies the relationship between the structure and acidity in TS-1 zeolite and brings forward a promising approach to develop better TS-1 zeolites by regulating the crystallization process.

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“…The H 2 O 2 decompositions over the two catalysts are both less than 8% under all conditions studied, and they become more severe with the increased temperature, decreased H 2 O 2 WHSV, and increased H 2 O 2 concentration. More decomposition occurs on the untreated TS‐1 than the treated one, probably due to the higher contents of anatase‐TiO 2 13 and “TiO 4 ” 40 in the former than those in the latter.…”

Section: Methodsmentioning

confidence: 98%

Kinetics simulation of propylene epoxidation over different Ti species in TS‐1

Zhang

Zuo

et al. 2021

AIChE Journal

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A thorough experimental investigation on the kinetic behavior of liquid‐phase propylene epoxidation over TS‐1 and tetrapropylammonium hydroxide (TPAOH) treated TS‐1 catalysts was conducted in a fixed‐bed reactor. The amounts of different coordinated Ti species in the catalysts were quantified by spectroscopies, and their catalytic performances of the epoxidation and alcoholysis of propylene oxide were measured by kinetic modeling. The study shows that the TPAOH treatment converted some of the tetrahedrally coordinated Ti to octahedrally coordinated Ti, and both species were active for the epoxidation and alcoholysis. The superior catalytic performance observed over the TPAOH treated TS‐1 is due to two factors, the increased percentage of active sites, and reduced energy barrier for epoxidation on the octahedrally coordinated Ti. In addition, as the H2O2 conversion increases, the adsorption equilibrium constant of propylene oxide plays a more decisive role than the activation energy for the selectivity of propylene glycol monomethyl ethers.

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Insights into the efficiency of hydrogen peroxide utilization over titanosilicate/H2O2 systems

Cited by 42 publications

References 121 publications

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Biophenol-Mediated Solvent-Free Synthesis of Titanium Silicalite-1 to Improve the Acidity Character of Framework Ti toward Catalysis Application

Kinetics simulation of propylene epoxidation over different Ti species in TS‐1

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