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Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti.

ABSTRACT: Titanium silicalite-1 (TS-1) with little extraframework Ti was hydrothermally synthesized in a tetrapropylammonium hydroxide system using starch as the additive. The influences of the amount of starch added on the coordination states of titanium ions and the functional mechanism of starch were studied by various characterization means. The addition of starch slowed the crystallization rate of TS-1 so that the insertion rate of titanium to the framework matched well with that of silicon. Therefore, the generation of extraframework Ti, including the anatase TiO₂ and octahedrally coordinated titanium, was eliminated. The catalytic performances of the TS-1 samples were evaluated in the epoxidation of 1-butene to produce butene oxide. The catalytic activity of TS-1 was improved significantly due to the increasing amount of framework Ti.

SUBMITTER: Zhang T

PROVIDER: S-EPMC6640744 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti.

Zhang Ting T Zuo Yi Y Liu Min M Song Chunshan C Guo Xinwen X

ACS omega 20161129 5

Titanium silicalite-1 (TS-1) with little extraframework Ti was hydrothermally synthesized in a tetrapropylammonium hydroxide system using starch as the additive. The influences of the amount of starch added on the coordination states of titanium ions and the functional mechanism of starch were studied by various characterization means. The addition of starch slowed the crystallization rate of TS-1 so that the insertion rate of titanium to the framework matched well with that of silicon. Therefor ...[more]

PMID: 31457180

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Project description:In this work, direct gas-phase epoxidation of propylene (DPO) to propylene oxide by molecular oxygen has been studied by using Ag-MoO3 supported on titanium-containing hexagonal mesoporous silica (Ti-HMS n ) of different Si/Ti molar ratios. The promotion effect of NaCl on the synthesized catalysts has also been investigated. Among the studied supports, the hexagonal mesoporous silica (HMS) with a Si/Ti ratio of 10 was the most suitable one for production of propylene oxide (PO). The optimal performance of the AgMo/Ti-HMS10 catalyst in DPO exhibited a selectivity to PO of 43.2% with a propylene conversion of 14.1%, at 400 °C, 0.1 MPa, and a space velocity of 12,000 h-1. The catalyst verified good stability over at least 20 h on stream. Only 2.7% PO selectivity with a propylene conversion of 10.1% was achieved over the AgMo/HMS sample. The incorporation of Ti into the HMS frame could optimize the particle size distribution of Ag, producing Ag nanoparticles with an average size of 6.8 nm compared with that of Ag/HMS (24.3 nm). The in situ Raman spectrum of AgMo/Ti-HMS10 heated in a stream of C3H6/He at 400 °C showed new bands at 616, 390, and 210 cm-1, characteristic of the Ag x Mo y O z intermediate phase. The obtained results suggested that this formed AgMo/Ti-HMS10 phase could most likely be relevant for selective epoxidation of propylene. However, during the reaction of C3H6 with AgMo/HMS, the formation of this intermediate was hardly detected. On the other hand, the hydrogen temperature-programmed reduction measurements indicated improved reducibility of MoO3 in the AgMo/Ti-HMS10 catalyst, which acknowledged the role of Mo6+ in gaining electrons from silver to form positively charged Ag. This could reduce the effective charge of the adsorbed oxygen on silver sites and in turn favor the epoxidation path of propylene rather than the combustion route. Also, during the reaction of C3H6 with NaAgMo/Ti-HMS10 at 400 °C, two new Raman bands were detected at 277 and 350 cm-1, characteristic of Ag2MoO4.

Project description:The catalytic performance with high conversion and high selectivity of Ti-based oxide catalysts have been widely investigated. Besides, stability, which is an essential parameter in the industrial process, lacked fundamental understanding. In this work, we combined computational and experimental techniques to provide insight into the deactivation of P25 and TS-1 Ti-based oxide catalysts during the methyl oleate (MO) epoxidation. The considered deactivation mechanisms are fouling and surface oxygen vacancy (OV). The fouling causes temporary catalyst deactivation through active site blockage but can be removed via calcination in air at high temperature. However, in this work, the OV formation plays an important role in the overall performance of the spent catalyst as the deactivated catalyst after regeneration, cannot be restored to the initial activity. Also, the effects of OV in spent catalysts caused (i) the formation of more Ti3+ species on the surface as evident by XPS and Bader charge analysis, (ii) the activity modification of the active region on the catalyst surface as the reduction in energy gap (Eg) occurred from the formation of the interstates observed in the density of states profiles of spent catalyst modeled by the O-vacant P25 and TS-1 models. This reduction in Eg affects directly the strength of Ti-OOH active site and MO bonding, in which high binding energy contributes to a low conversion because the MO needed an O atom from Ti-OOH site to form the methyl-9,10-epoxy stearate. Hence, the deactivation of the Ti-based oxide catalysts is caused not only by the insoluble by-products blocking the active region but also mainly from the OV. Note that the design of reactive and stable Ti-based oxide catalysts for MO epoxidation needed strategies to prevent OV formation that permanently deactivated the active region. Thus, the interrelation and magnitude between fouling and OV formation on catalyst deactivation will be investigated in future works.

Dataset Information

Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti.

Publications

Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti.

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