排序方式: 共有270条查询结果,搜索用时 15 毫秒
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Yuxiang Chen Ke Gong Dr. Feng Jiao Prof. Xiulian Pan Prof. Guangjin Hou Prof. Rui Si Prof. Xinhe Bao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6591-6596
Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn2+-ion exchanged ZSM-5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO2) at 20 % CO conversion. NMR spectroscopy, X-ray absorption spectroscopy, and X-ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM-5. Quasi-in-situ solid-state NMR, obtained by quenching the reaction in liquid N2, detects C2 species such as acetyl (-COCH3) bonding with an oxygen, ethyl (-CH2CH3) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C−C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn2+-ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ-13, MCM-22, and ZSM-12) all give ethane predominantly. By contrast, a physical mixture of ZnO-ZSM-5 favors formation of hydrocarbons beyond C3+. These results provide an important guide for tuning the product selectivity in syngas conversion. 相似文献
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Victor Y. Mao Dr. Phillip J. Milner Dr. Jung-Hoon Lee Dr. Alexander C. Forse Eugene J. Kim Rebecca L. Siegelman Dr. C. Michael McGuirk Leo B. Zasada Prof. Jeffrey B. Neaton Prof. Jeffrey A. Reimer Prof. Jeffrey R. Long 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19636-19645
A series of structurally diverse alcoholamine- and alkoxyalkylamine-functionalized variants of the metal–organic framework Mg2(dobpdc) are shown to adsorb CO2 selectively via cooperative chain-forming mechanisms. Solid-state NMR spectra and optimized structures obtained from van der Waals-corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO2 adsorbents, providing further means of optimizing these powerful materials for energy-efficient CO2 separations. 相似文献
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Dr. Baptiste Joalland Nuwandi M. Ariyasingha Dr. Sören Lehmkuhl Prof. Thomas Theis Prof. Stephan Appelt Prof. Eduard Y. Chekmenev 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8732-8738
Radio amplification by stimulated emission of radiation (RASER) was recently discovered in a low-field NMR spectrometer incorporating a highly specialized radio-frequency resonator, where a high degree of proton-spin polarization was achieved by reversible parahydrogen exchange. RASER activity, which results from the coherent coupling between the nuclear spins and the inductive detector, can overcome the limits of frequency resolution in NMR. Here we show that this phenomenon is not limited to low magnetic fields or the use of resonators with high-quality factors. We use a commercial bench-top 1.4 T NMR spectrometer in conjunction with pairwise parahydrogen addition producing proton-hyperpolarized molecules in the Earth's magnetic field (ALTADENA condition) or in a high magnetic field (PASADENA condition) to induce RASER without any radio-frequency excitation pulses. The results demonstrate that RASER activity can be observed on virtually any NMR spectrometer and measures most of the important NMR parameters with high precision. 相似文献
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