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Dan Xie

Bio: Dan Xie is an academic researcher from Chevron Corporation. The author has contributed to research in topics: Molecular sieve & Zeolite. The author has an hindex of 26, co-authored 106 publications receiving 1519 citations. Previous affiliations of Dan Xie include ETH Zurich & Central South University.


Papers
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Journal ArticleDOI
TL;DR: A similar approach, using the powder charge-flipping algorithm to combine the two types of data and molecular modelling to help to locate the structure-directing agent was applied to SSZ-74, which revealed a most unusual 23-Si-atom framework structure with ordered Si vacancies.
Abstract: Elucidation of the framework structure of zeolites can sometimes prove difficult. The combination of powder diffraction and electron microscopy using a charge-flipping algorithm enables ordered silicon vacancies in a zeolite catalyst to be revealed.

146 citations

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TL;DR: A new zeolite, related to the DeNOx catalyst Cu-SSZ-13, has been synthesized using an unusual polycyclic quaternary ammonium cation as the structure-directing agent and has considerable potential as a catalyst in the areas of gas conversion and sequestration.
Abstract: A new zeolite (SSZ-52, vertical bar(C14H28N)(6)Na-6(H2O)(18)vertical bar[Al12Si96O216]), related to the DeNOx catalyst Cu-SSZ-13 (CHA framework type), has been synthesized using an unusual polycyclic quaternary ammonium cation as the structure-directing agent. By combining X-ray powder diffraction (XPD), high-resolution transmission electron microscopy (HRTEM) and molecular modeling techniques, its porous aluminosilicate framework structure (R (3) over barm, a = 13.6373(1) angstrom, c = 44.7311(4) angstrom), which can be viewed as an 18-layer stacking sequence of hexagonally arranged (Si,Al)(6)O-6 rings (6-rings), has been elucidated. The structure has a three-dimensional 8-ring channel system and is a member of the ABC-6 family of zeolites (those that can be described in terms of 6-ring stacking sequences) like SSZ-13, but it has cavities that are twice as large. The code SFW has been assigned to this new framework type. The large cavities contain pairs of the bulky organic cations. HRTEM and XPD simulations show that stacking faults do occur, but only at the 5-10% level. SSZ-52 has considerable potential as a catalyst in the areas of gas conversion and sequestration.

83 citations

Journal ArticleDOI
TL;DR: In this paper, a microwave-assisted liquid phase synthesis route to LiFePO4 doped with divalent (Mn, Ni, Zn), trivalent (Al) and tetravalent(Ti) metal ions in varying concentrations is presented.
Abstract: A microwave-assisted liquid-phase synthesis route to LiFePO4 doped with divalent (Mn, Ni, Zn), trivalent (Al) and tetravalent (Ti) metal ions in varying concentrations is presented. In spite of the low synthesis temperature of 180 °C all the as-synthesized powders are highly crystalline. The short reaction times of just a few minutes represent the basis for an efficient and time-saving screening of different types of dopants with respect to optimized electrochemical performance in lithium-ion batteries. The Ni- and Zn-doped LiFePO4 with nominal dopant concentrations of 7 and 2 mol%, respectively, outperformed all the other samples, offering initial specific charge of 168 A h kg−1 and excellent capacity retention of 97% after 300 full cycles. A discharge rate of 8 C still resulted in 152 A h kg−1 after 50 cycles. The electrochemical investigations are accompanied by a detailed structural and morphological characterization. Whereas the elemental composition, obtained from quantitative energy dispersive X-ray (EDX) analysis, and the electric conductivity could not directly be correlated to the electrochemical performance, the Rietveld analysis showed that the better the fit the better the electrochemical performance. This observation points to a relation between the phase-purity of a sample and its electrochemical properties.

81 citations

Journal ArticleDOI
TL;DR: Comparative synthetic studies demonstrate that this new delamination method requires a borosilicate layered zeolite precursor, in which boron atoms can be isomorphously substituted by aluminum, neutral amine pore fillers instead of rigid and large quaternary amine SDAs, and careful temperature control.
Abstract: Layered borosilicate zeolite precursor ERB-1P (Si/B = 11) is delaminated via isomorphous substitution of Al for B using a simple aqueous Al(NO_3)_3 treatment. Characterization by PXRD shows loss of long-range order, and TEM demonstrates transformation of rectilinear layers in the precursor to single and curved layers in the delaminated material. N_2 physisorption and base titration confirm the expected decrease of micropore volume and increase in external surface area for delaminated materials relative to their calcined 3D zeolite counterpart, whereas FTIR and multinuclear NMR spectroscopies demonstrate synthesis of Bronsted acid sites upon delamination. Comparative synthetic studies demonstrate that this new delamination method requires (i) a borosilicate layered zeolite precursor, in which boron atoms can be isomorphously substituted by aluminum, (ii) neutral amine pore fillers instead of rigid and large quaternary amine SDAs, and (iii) careful temperature control, with the preferred temperature window being around 135 °C for ERB-1P delamination. Acylation of 2-methoxynaphthalene was used as a model reaction to investigate the catalytic benefits of delamination. A partially dealuminated delaminated material displays a 2.3-fold enhancement in its initial rate of catalysis relative to the 3D calcined material, which is nearly equal to its 2.5-fold measured increase in external surface area. This simple, surfactant- and sonication-free, mild delamination method is expected to find broad implementation for the synthesis of delaminated zeolite catalysts.

81 citations


Cited by
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TL;DR: ToposPro as mentioned in this paper is a topological analysis of crystal structures realized in the current version of the program package ToposPro, which can be used to analyze various classes of chemical compounds including coordination polymers, molecular crystals, supramolecular ensembles, inorganic ionic compounds, intermetallics, fast-ion conductors, microporous materials.
Abstract: Basic concepts of computer topological analysis of crystal structures realized in the current version of the program package ToposPro are considered. Applications of the ToposPro methods to various classes of chemical compounds—coordination polymers, molecular crystals, supramolecular ensembles, inorganic ionic compounds, intermetallics, fast-ion conductors, microporous materials—are illustrated by many examples. It is shown that chemically and crystallographically different structures can be automatically treated in a similar way with the ToposPro approaches.

2,232 citations

Journal ArticleDOI
TL;DR: This review addresses recent advances made in studies of hierarchically porous materials and methods to control their structure and morphology and hopes that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information.
Abstract: Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

941 citations

Journal ArticleDOI
TL;DR: This Review provides both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs.
Abstract: Defect engineering in metal–organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of “defect-engineering” concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.

847 citations

Journal ArticleDOI
TL;DR: The BOLS correlation mechanism has been initiated and intensively verified as discussed by the authors, which has enabled the tunability of a variety of properties of a nanosolid to be universally reconciled to the effect of bond order deficiency of atoms at sites surrounding defects or near the surface edges of the nano-material.

775 citations