Profiles

Ning Yuan

Ning Yuan

PhD Student

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Arbetar vid Institutionen för material- och miljökemi
E-post ning.yuan@mmk.su.se
Besöksadress Svante Arrhenius väg 16 C
Rum C 570
Postadress Institutionen för material- och miljökemi 106 91 Stockholm

Om mig

Under min tid som gemensamdoktorand vid Stockholms universitet och Sveriges lantbruksuniversitet, har projektledning i samarbeten mellan forskargrupper blivit centralt för mig för att kunna uppnå de höga krav som ställs på min forskning. Stort ansvar, engagemang och ledarskap har visat sig vara mina styrkor – vilka lett till stora projektframgångar där jag publicerat resultat i världsledande facktidskrifter. Med min kinesiska bakgrund och mina åtta år i Sverige med fru och barn, har jag fått för en ovärderliga kunskaper i interkulturella relationer.

Jag gillar sociallt liv och hade jobbat som vice-ordförande och ombusman för doktorander vid institutionens doktorandråd i två år. Jag är också intresserad av språk. Förutom mandarin som är mitt modersmål är jag bra på engelska och svenska.

Undervisning

Jag har jobbat som en lärarassistent i ett år (fyra terminer) och handlett totalt ca. 80 kandidat studenter i två laborationskurser i kemi med bra arbetes utvärderingar.

Forskning

Mina projekt fokuserar huvudsakligen på användning av en avancerad teknik som heter röntgenabsorptionsspektroskopi (XAS) för att undersöka de katalytiska aktiva arterna i heterogena och homogena katalysatorer i realtid under reaktioner, tillsammans med deaktiveringsmekanismen av katalysatorn.

Jag har också erfarenheter av syntes och karakteriseringar av metallorganikst ramverk (MOFs) som en typ av funktionella porösa material med användningar i katalys och gassorption.

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2018. Ning Yuan (et al.). Journal of the American Chemical Society 140 (26), 8206-8217

    The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (H-1 NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl- ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.

  • 2019. Ning Yuan (et al.). Catalysis Science & Technology 9, 2025-2031

    In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(II) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. A Pd(II) N-heterocyclic carbene complex p-stacked onto reduced graphene oxide (rGO) was used as catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(II) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(II) are replaced by other ligands with a bond distance to Pd corresponding to carbon, nitrogen and/or oxygen (L). Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(IV) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(IV) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(II)-Pd(IV)-Pd(II) reaction mechanism.

  • 2018. Ning Yuan (et al.). Scientific Reports 8

    Postsynthetic reactions of metal-organic frameworks (MOFs) are versatile tools for producing functional materials, but the methods of evaluating these reactions are cumbersome and destructive. Here we demonstrate and validate the use of in situ NMR spectroscopy of species in the liquid state to examine solvent-assisted ligand exchange (SALE) and postsynthetic modification (PSM) reactions of metal-organic frameworks. This technique allows functionalization to be monitored over time without decomposing the product for analysis, which simplifies reaction screening. In the case of SALE, both the added ligand and the ligand leaving the framework can be observed. We demonstrate this in situ method by examining SALE and PSM reactions of the robust zirconium MOF UiO-67 as well as SALE with the aluminum MOF DUT-5. In situ NMR spectroscopy provided insights into the reactions studied, and we expect that future studies using this method will permit the examination of a variety of MOF-solute reactions.

  • 2019. Ning Yuan (et al.).

    The cause and mechanism of deactivation of a well-studied heterogeneous palladium(II) catalyst in the intramolecular lactonization of acetylenic acids to γ-alkylidene lactones have been investigated. It was shown that the deactivation was driven by the formation of reduced palladium species following the addition of the base triethylamine. In this work, X-ray absorption spectroscopy (XAS) was used to identify the palladium species and follow their evolution over the course of the reaction. It was also found that the choice of substrates has significant influences on the Pd species under the same reaction conditions. With these insights into the deactivation mechanism derived from XAS, different strategies were tested and illustrated to regain or maintain the active state of the catalyst. This information was further used to develop a new protocol, which can effectively prevent the deactivation of the catalyst and prolong its usage. 

  • 2017. Alexandre Bruneau (et al.). Chemistry - A European Journal 23 (52), 12886-12891

    Herein, we report on the utilization of a heterogeneous catalyst, consisting of Pd nanoparticles supported on a siliceous mesocellular foam (Pd-0-AmP-MCF), for the synthesis of heterocycles. Reaction of o-iodophenols and protected o-iodoanilines with acetylenes in the presence of a Pd nanocatalyst produced 2-substituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands. Moreover, the structure of the reported Pd nanocatalyst was further elucidated with extended X-ray absorption fine-structure spectroscopy, and it was proven that the catalyst could be recycled multiple times without significant loss of activity.

  • 2016. Ahmed S. Etman (et al.). Journal of Materials Chemistry A 4 (46), 17988-18001

    The synthesis of two dimensional (2D) materials from transition metal oxides, chalcogenides, and carbides mostly involve multiple exfoliation steps in which hazardous solvents and reagents are used. In this study, hydrated vanadium pentoxide (V2O5 center dot nH(2)O) nanosheets with a thickness of a few nanometers were prepared via a facile environmentally friendly water based exfoliation technique. The exfoliation process involved refluxing the precursor, vanadium dioxide (VO2(B)), in water for a few days at 60 degrees C. The proposed exfoliation mechanism is based on the intercalation/insertion of water molecules into the VO2(B) crystals and the subsequent cleavage of the covalent bonds holding the layers of VO2(B) together. The thermal and chemical analyses showed that the approximate chemical composition of the nanosheets is H0.4V2O5 center dot 0.55H(2)O, and the percentage of V-V content to that of V-IV in the nanosheets is about 80(3)% to 20(3)%. The exfoliated aqueous suspension of the V2O5 center dot 0.55H(2)O nanosheets was successfully deposited onto multi-walled carbon nanotube (MW-CNT) paper to form free-standing electrodes with a thickness of the V2O5 center dot 0.55H(2)O layer ranging between 45 and 4 mu m. A series of electrochemical tests were conducted on the electrodes to determine the cyclability and rate capability of lithium insertion into V2O5 center dot 0.55H(2)O nanosheets. The electrodes with the thinnest active material coating (similar to 4 mu m) delivered gravimetric capacities of up to 480 and 280 mA h g(-1) when cycled at current densities of 10 and 200 mA g(-1), respectively.

  • Karl P. J. Gustafson (et al.).
  • Karl P. J. Gustafson (et al.).
  • Junzhong Lin (et al.).

    Zeolites are type of microporous crystalline material which have been widely used in various aspects of industry, such as separation, adsorption, and catalysis. However, great diffusion limitation can be provoked due to small pore size of mircoporus framework in catalytic reactions. Hierarchical zeolites have been proved to be a successful alternative to solve the diffusion problem. Particularly, the synthesis of hierarchical porous zeolite by swelling and pillaring lamellar MWW zeolitic precursor has been proved as an efficient approach to solve the diffusion limitations in the catalytic reactions. In this work, hierarchical MWW zeolite has been synthesized by swelling and pillaring of lamellar MWW zeolitic precursor (MCM-22) using D4R building units. The synthesis procedure has been carefully studied by various characterization methods, such as PXRD, TEM, N2 adsorption-desorption and etc.

  • Junzhong Lin (et al.).

    Hierarchical porous materials as catalyst have provoked great attention recent years considering that it can offer enhanced molecular diffusion and mass transfer during the reaction. Titanium containing hierarchical porous silicate material has been successfully synthesized in present work. Double-four-ring units were used as the basic building blocks to construct the desired material. Both micropores and mesopores were found in the as synthesized material. The local structure of incorporated titanium species was carefully studied using various characterization techniques, such as XPS, UV-vis, XANES and EXAFS. Tetrahedral coordinated titanium can be mostly found in the as synthesized material in this work, the distorted the local structure was further revealed by using EXAFS.

Visa alla publikationer av Ning Yuan vid Stockholms universitet

Senast uppdaterad: 17 januari 2020

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