Operando DB-FTIR and DFT results certificate that the isobutane aromatization could be exclusively catalyzed by (Zn–O–Zn)2+ Lewis acid site over Zn/HZSM-5.

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.

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We report herein the preparation, characterization, and catalytic performance of a series of heterogeneous catalysts featuring highly dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials are evaluated in the CO2-assisted oxidative ethane dehydrogenation, a very important reaction for the synthesis of platform chemicals. In particular, we find that Zn2.92/SSZ-13 exhibits high reactivity in the conversion of C2H6 and CO2 and high ethene selectivity. In line with the experimental results, we show that the selective character of the catalyst is due to the characteristic compositional structure of the support and its topology that can effectively confine CO2 molecules. An in-depth molecular analysis via operando studies and DFT calculations shows that the rate-limiting step of the reaction with CO2 is the second C–H bond dissociation to give C2H4. The addition of CO2 effectively reduces the energy barrier of this step, favoring desorption of C2H4 while limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of catalysts made of highly dispersed zinc species on zeolites in relevant transformations.