Chemical and Biomolecular Engineering Research Works

Permanent URI for this collectionhttp://hdl.handle.net/1903/1656

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Author: search.filters.author.Liu, Dongxia

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    Two-Dimensional Zeolite Materials: Structural and Acidity Properties
    (MDPI, 2020-04-12) Schulman, Emily; Wu, Wei; Liu, Dongxia
    Zeolites are generally defined as three-dimensional (3D) crystalline microporous aluminosilicates in which silicon (Si4+) and aluminum (Al3+) are coordinated tetrahedrally with oxygen to form large negative lattices and consequent Brønsted acidity. Two-dimensional (2D) zeolite nanosheets with single-unit-cell or near single-unit-cell thickness (~2–3 nm) represent an emerging type of zeolite material. The extremely thin slices of crystals in 2D zeolites produce high external surface areas (up to 50% of total surface area compared to ~2% in micron-sized 3D zeolite) and expose most of their active sites on external surfaces, enabling beneficial effects for the adsorption and reaction performance for processing bulky molecules. This review summarizes the structural properties of 2D layered precursors and 2D zeolite derivatives, as well as the acidity properties of 2D zeolite derivative structures, especially in connection to their 3D conventional zeolite analogues’ structural and compositional properties. The timeline of the synthesis and recognition of 2D zeolites, as well as the structure and composition properties of each 2D zeolite, are discussed initially. The qualitative and quantitative measurements on the acid site type, strength, and accessibility of 2D zeolites are then presented. Future research and development directions to advance understanding of 2D zeolite materials are also discussed.
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    Noble Metal Ion-Directed Assembly of 2D Materials for Heterostructured Catalysts and Metallic Micro-Texturing
    (Wiley, 2023-05-07) Little, Joshua M.; Sun, Jiayue; Kamali, Ali; Chen, Amy; Leff, Asher C.; Li, Yang; Borden, Leah K.; Dissanayake, Thilini U.; Essumang, Deborah; Oseleononmen, Benita O.; Liu, Dongxia; Woehl, Taylor J.; Chen, Po-Yen
    Assembling 2D-material (2DM) nanosheets into micro- and macro-architectures with augmented functionalities requires effective strategies to overcome nanosheet restacking. Conventional assembly approaches involve external binders and/or functionalization, which inevitably sacrifice 2DM's nanoscale properties. Noble metal ions (NMI) are promising ionic crosslinkers, which can simultaneously assemble 2DM nanosheets and induce synergistic properties. Herein, a collection of NMI–2DM complexes are screened and categorized into two sub-groups. Based on the zeta potentials, two assembly approaches are developed to obtain 1) NMI-crosslinked 2DM hydrogels/aerogels for heterostructured catalysts and 2) NMI–2DM inks for templated synthesis. First, tetraammineplatinum(II) nitrate (TPtN) serves as an efficient ionic crosslinker to agglomerate various 2DM dispersions. By utilizing micro-textured assembly platforms, various TPtN–2DM hydrogels are fabricated in a scalable fashion. Afterward, these hydrogels are lyophilized and thermally reduced to synthesize Pt-decorated 2DM aerogels (Pt@2DM). The Pt@2DM heterostructures demonstrate high, substrate-dependent catalytic activities and promote different reaction pathways in the hydrogenation of 3-nitrostyrene. Second, PtCl4 can be incorporated into 2DM dispersions at high NMI molarities to prepare a series of PtCl4–2DM inks with high colloidal stability. By adopting the PtCl4–graphene oxide ink, various Pt micro-structures with replicated topographies are synthesized with accurate control of grain sizes and porosities.
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    Understanding the Impact of Hydrogen Activation by SrCe 0.8Zr0.2O 3−δ Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion
    (Frontiers, 2022-01-10) Cheng, Sichao; Oh, Su Cheun; Sakbodin, Mann; Qiu, Limei; Diao, Yuxia; Liu, Dongxia
    Understanding the Impact of Hydrogen Activation by SrCe 0.8Zr0.2O 3−δ Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion Sichao Cheng 1†, Su Cheun Oh 1†, Mann Sakbodin 1 , Limei Qiu 2 , Yuxia Diao 2 and Dongxia Liu 1 * 1 Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, United States, 2 Research Institute of Petroleum Processing, SINOPEC, Beijing, China Direct non-oxidative methane conversion (DNMC) converts methane (CH 4 ) in one step to olefin and aromatic hydrocarbons and hydrogen (H 2) co-product. Membrane reactors comprising methane activation catalysts and H 2 -permeable membranes can enhance methane conversion by in situ H 2 removal via Le Chatelier’s principle. Rigorous description of H 2 kinetic effects on both membrane and catalyst materials in the membrane reactor, however, has been rarely studied. In this work, we report the impact of hydrogen activation by hydrogen-permeable SrCe 0.8Zr 0.2O 3−δ (SCZO) perovskite oxide material on DNMC over an iron/silica catalyst. The SCZO oxide has mixed ionic and electronic conductivity and is capable of H2 activation into protons and electrons for H 2 permeation. In the fixed- bed reactor packed with a mixture of SCZO oxide and iron/silica catalyst, stable and high methane conversion and low coke selectivity in DNMC was achieved by co-feeding of H 2 in methane stream. The characterizations show that SCZO activates H 2 to favor “soft coke” formation on the catalyst. The SCZO could absorb H 2 in situ to lower its local concentration to mitigate the reverse reaction of DNMC in the tested conditions. The co-existence of H 2 co-feed, SCZO oxide, and DNMC catalyst in the present study mimics the conditions of DNMC in the H2 -permeable SCZO membrane reactor. The findings in this work offer the mechanistic understanding of and guidance for the design of H2 -permeable membrane reactors for DNMC and other alkane dehydrogenation reactions.