The effect of T-atom ratio and TPAOH concentration on the pore structure and titanium position in MFI-Type titanosilicate during dissolution-recrystallization process

Jiao, Yilai; Adedigba, Abdul-Lateef; Dummer, Nicholas F.; Liu, Jinmin; Zhou, Yangtao; Guan, Yanan; Shen, Hengyu; Perdjon, Michal

doi:10.1016/j.micromeso.2020.110397

Cited by 21 publications

(10 citation statements)

References 18 publications

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“…XRD patterns were consistent with those reported for titanium MFI zeotypes previously. , The lack of splitting of the peak at 2θ = 24.6° indicates the presence of the orthorhombic unit cell (see Figure S.2b). Nitrogen adsorption isotherms for TS-1 and S-1 samples were typical of the MFI structure, and micropore volumes were consistent with values typically reported for TS-1 (micropore volumes = 0.16–0.18 cm 3 g –1 ). ,, …”

Section: Resultssupporting

confidence: 88%

“…17,20 The lack of splitting of the peak at 2θ = 24.6°indicates the presence of the orthorhombic unit cell (see Figure S.2b). 29 Nitrogen adsorption isotherms for TS-1 and S-1 samples were typical of the MFI structure, and micropore volumes were consistent with values typically reported for TS-1 (micropore volumes = 0.16−0.18 cm 3 g −1 ). 17,20,30 DRUV−vis spectra indicated the presence of primarily isolated Ti 4+ sites in TS-1.…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

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Kinetics of Propylene Epoxidation over Extracrystalline Gold Active Sites on AU/TS-1 Catalysts

Arvay

Wang

et al. 2022

ACS Catal.

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To determine whether the catalytic roles of extracrystalline and intracrystalline gold nanoparticles supported on titanosilicate-1 (TS-1) for direct propylene epoxidation are intrinsically different, the kinetics of direct propylene epoxidation were measured in a gas-phase continuous stirred tank reactor (CSTR) over polyvinylpyrrolidone-coated (PVP) gold nanoparticles (Au-PVP/TS-1) deposited on TS-1. The as-made PVPcoated gold nanoparticles were too large to fit into the micropores of TS-1, even after ligands were removed in situ by a series of pretreatments, as confirmed by both TEM and TGA-DSC. The activation energy (51 kJ mol −1 ) and reaction orders for H2 (1.3), O 2 (0.4), propylene (0.4), propylene oxide (−0.6), carbon dioxide (0), and water (0) for propylene epoxidation measured on Au-PVP/TS-1 were consistent with those reported for Au/TS-1 prepared via deposition-precipitation (Au-DP/TS-1) (52 kJ mol −1 , H 2 , 1; O 2 , 0.4; C 3 H 6 , 0.4; C 3 H 6 O, −0.6; CO 2 , 0; H 2 O, 0). However, while the reaction orders for hydrogen oxidation on Au-PVP/TS-1 (H 2 , 0.8; O 2 , 0; C 3 H 6 , −0.3; C 3 H 6 O, −0.1; CO 2 , 0; H 2 O, −0.2) were similar to those measured on Au-DP/TS-1 (H 2 , 0.9; O 2 , 0.3; C 3 H 6 , −0.3; C 3 H 6 O, 0; CO 2 , 0; H 2 O, −0.1), a decrease in activation energy from approximately 30 kJ mol −1 for Au-DP/TS-1 to 4− 5 kJ mol −1 for Au-PVP/TS-1 suggests there is a change in rate-limiting step or active site for hydrogen oxidation. Additionally, an active site model was developed which determines the number of Ti within an interaction range of the perimeter of extracrystalline Au nanoparticles (i.e., the number of Au−Ti active site pairs). This model was used to estimate catalytic turnover frequencies over solely proximal Au−Ti pairs, assuming that hydrogen peroxide does not desorb and migrate from Au sites to Ti sites and instead propylene oxide forms in a concerted mechanism previously termed the "simultaneous" mechanism. Turnover frequencies estimated for this active site model for a data set containing both Au-DP/TS-1 and Au-PVP/TS-1 were ∼20× higher than the highest previous reported estimates (∼80 s −1 vs 1−5 s −1 at 473 K) for catalytic oxidation on noble metals, suggesting that the simultaneous mechanism occurring over proximal Au−Ti sites alone is incapable of explaining the observed rate of propylene epoxidation and that short-range migration of hydrogen peroxide is kinetically relevant. The agreement of reaction orders, activation energy, and active site model for propylene epoxidation on both Au-DP/TS-1 and Au-PVP/TS-1 suggests a common mechanism for propylene epoxidation on both catalysts containing small intraporous gold clusters and catalysts with exclusively larger extracrystalline gold nanoparticles. Rates of hydrogen oxidation were found to vary proportionally to the amount of surface gold atoms. This is also consistent with the hypothesis that the observed decrease in hydrogen efficiency and PO site-time-yield per gold mass with increasing gold loading are driven primarily by t...

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Section: Resultssupporting

confidence: 88%

Section: ■ Experimental Methodsmentioning

confidence: 99%

Kinetics of Propylene Epoxidation over Extracrystalline Gold Active Sites on AU/TS-1 Catalysts

Arvay

Wang

et al. 2022

ACS Catal.

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“…The findings suggest that the treatment using 0.5 M TPAOH and the parent TS-1 with a Si/Ti ratio of 46 can facilitate the conversion of extraframework Ti into the framework ones and create TS-1 with interconnected open meso-/macropore in TS-1. Unfortunately, the method is not suitable for treating the parent TS-1 with lower Si/Ti ratios of <46 since the framework Ti in the parent can hinder the dissolution/desiliconization process under alkaline conditions . The same issue was also encountered during the alkaline post-treatment of ZSM-5 zeolites .…”

Section: Introductionmentioning

confidence: 99%

Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis

Yang

Guan

et al. 2023

Crystal Growth & Design

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This work presents the development and systematic study of a method to prepare hierarchical titanium silicalite-1 (TS-1) zeolites with high tetra-coordinated framework Ti species content. The new method involves (i) the synthesis of the aged dry gel by treating the zeolite precursor at 90 °C for 24 h; and (ii) the synthesis of hierarchical TS-1 by treating the aged dry gel using tetrapropylammonium hydroxide (TPAOH) solution under hydrothermal conditions. Systematic studies were conducted to understand the effect of the synthesis conditions (including the TPAOH concentration, liquid-to-solid ratio, and treatment time) on the physiochemical properties of the resulting TS-1 zeolites, and the results showed that the condition of a TPAOH concentration of 0.1 M, liquid-tosolid ratio of 1.0, and treatment time of 9 h was ideal to enable the synthesis of hierarchical TS-1 with a Si/Ti ratio of 44. Importantly, the aged dry gel was beneficial to the quick crystallization of zeolite and assembly of nanosized TS-1 crystals with a hierarchical structure (S ext = 315 m 2 g −1 and V meso = 0.70 cm 3 g −1 , respectively) and high framework Ti Species content, making the accessible active sites ready for promoting oxidation catalysis.

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“…In contrast, high concentrations of TPAOH are ineffective for the re-insertion of TiO 2 for silica-rich TS-1. 26 Up to date, there are few reports on the synthesis of anatase-free hollow TS-1 with tunable titanium micro-environments. More importantly, the key factors affecting the heteroatom micro-environment in zeolites have remained elusive so far.…”

Section: Introductionmentioning

confidence: 99%

Functional mother liquor reversed titanium species for the green synthesis of anatase-free hollow TS-1 with tunable titanium micro-environment via a kinetic-thermodynamic co-regulatory pathway

Zhai

Wang

Zhang

et al. 2022

Mater. Chem. Front.

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The effect of T-atom ratio and TPAOH concentration on the pore structure and titanium position in MFI-Type titanosilicate during dissolution-recrystallization process

Abstract: Graham J. (2020) 'The eect of T-atom ratio and TPAOH concentration on the pore structure and titanium position in MFI-Type titanosilicate during dissolution-recrystallization process.', Microporous and mesoporous materials., 305 . p. 110397.

Cited by 21 publications

References 18 publications

Kinetics of Propylene Epoxidation over Extracrystalline Gold Active Sites on AU/TS-1 Catalysts

Kinetics of Propylene Epoxidation over Extracrystalline Gold Active Sites on AU/TS-1 Catalysts

Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis

Functional mother liquor reversed titanium species for the green synthesis of anatase-free hollow TS-1 with tunable titanium micro-environment via a kinetic-thermodynamic co-regulatory pathway

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