Mesoporous Titanium-Silicalite Zeolite Containing Organic Templates as a Bifunctional Catalyst for Cycloaddition of CO₂ and Epoxides

Abstract

Mesoporous TS-1 (MTS-1) containing organic templates tetrapropylammonium hydroxide (TPAOH) and polydiallyldimethylammonium chloride is synthesized and treated with different concentrations of hydrochloric acid aqueous solution. The as-synthesized MTS-1 are characterized using X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, transmission electron microscopy, UV-vis, C cross-polarization/magic angle spinning (CP/MAS) NMR, thermogravimetry analysis, CO-temperature-programmed desorption (TPD), N adsorption-desorption, X-ray fluorescence, and elemental analysis. The results of C CP/MAS NMR show that the structures of organic templates are retained after acid washing treatment. Not required to be removed by calcination, the organic templates embedded in MTS-1 can take the role of basic sites and activate carbon dioxide (CO), which is confirmed by FT-IR. Moreover, the amount of acid sites and basic sites in the samples before and after acid treatment is characterized by modified Hammett indicator method and CO-TPD, respectively. The results show that both the acidity and the basicity in the material are improved after acid washing. Thus, the sample after acid treatment contains two active sites: basic sites stemming from organic species and acid sites coming from framework Ti, which is beneficial to be used as a bifunctional catalyst in the cycloaddition reaction of CO and epoxides. It is highly active in the cycloaddition reaction, in which the conversion of epichlorohydrin (ECH) could reach 97.8% and the selectivity of cyclic carbonate is 98.0% under 1.6 MPa at 393 K for 6 h when acetonitrile is used as a solvent. Moreover, the kinetics of the cycloaddition reaction are studied using ECH as a substrate by varying the reaction parameters. More importantly, the organic-inorganic hybrid catalyst is reusable and stable against leaching of organic species in the cycloaddition reaction.

Facile preparation of bi-functional iron doped mesoporous materials and their application in the cycloaddition of CO2

“…There is no doubt that the presence of organic species provides a large number of N-containing groups for these materials, which is conducive to the activation of CO 2 . This is consistent with the results of our previous study that amine groups of organic species (PDDA) can interact with CO 2 [29] . In addition, the amount of accessible basic sites in these samples could be calculated based on the integrated peak areas.…”

“…This phenomenon can be interpreted as the following reasons: (a) there is an electrostatic repulsion between CTA + ions and PDDA in the synthetic system; (b) there is competitive effect of silicate-CTA + / silicate-DDA micelles and silicate-PDDA; (c) the presence of PDDA leads to the no-uniform hydrolysis of silicon alkoxides. In addition, the S BET and V Meso of Fe-HMS and Fe-MCM-41 materials are larger than those of MTS-1 [29] , which is due to the removal of the conventional surfactants DDA or CTAB.…”

“…Characterization methods and the corresponding instrument information are the same as previous literature [18,29] .…”

“…Recently, mesoporous TS-1 material has been synthesized by our group, which is used as an effective bi-functional catalyst in CO 2 cycloaddition [29] . The results show that amine groups in organic species (polydiallyldimethylammonium chloride, PDDA) can be used as basic sites to activate CO 2 .…”

Characterization of Metal‐zeolite Composite Catalysts: Determining the Environment of the Active Phase

“…Similar TPD profiles can be conducted with other adsorbate molecules, such as CO 2 , which is a Lewis acid and has been used to characterize basicity in mesoporous TS‐1 . In addition to probing the strength of basic sites within the catalyst, the authors measure the capacity of CO 2 adsorption after acid treatment to determine if TS‐1 is a viable catalyst for the cycloaddition of CO 2 to epoxides.…”