Now showing items 1-20 of 2489

    • Silicon carbide in catalysis: from inert bed filler to catalytic support and multifunctional material

      Kulkarni, Shekhar Rajabhau; Velisoju, Vijay Kumar; Tavares, F.; Dikhtiarenko, Alla; Gascon, Jorge; Castaño, Pedro (Catalysis Reviews, Informa UK Limited, 2022-01-22) [Article]
      Silicon carbide (SiC) or carborundum has unparalleled thermal stability and conductivity compared with many other materials. This feature together with its unique photoelectrical properties (tunable band gap: 2.39–3.33 eV), low thermal expansion, high strength, and good chemical and thermal stability makes it an ideal inert solid in catalysis. The evolution of methods for synthesizing SiC has also progressively endowed it with additional features at the multiscale. This review tracks the development of SiC from a secondary to a leading role material in catalysis. First, the intrinsic properties of SiC are discussed and compared with other state-of-the-art catalytic materials. The synthetic methods are systematically reviewed and compared. Then, the applications of SiC in catalysis are assessed, paying particular attention to those that involve C1 chemistry (Fischer–Tropsch Synthesis and the valorization of CO2 and CH4), photocatalysis and biomass conversion. Finally, the potential future applications of SiC are also addressed and discussed.
    • Self-Assembly and Regrowth of Metal Halide Perovskite Nanocrystals for Optoelectronic Applications

      Liu, Jiakai; Zheng, Xiaopeng; Mohammed, Omar F.; Bakr, Osman (Accounts of Chemical Research, American Chemical Society (ACS), 2022-01-16) [Article]
      Conspectus Over the past decade, the impressive development of metal halide perovskites (MHPs) has made them leading candidates for applications in photovoltaics (PVs), X-ray scintillators, and light-emitting diodes (LEDs). Constructing MHP nanocrystals (NCs) with promising optoelectronic properties using a low-cost approach is critical to realizing their commercial potential. Self-assembly and regrowth techniques provide a simple and powerful “bottom-up” platform for controlling the structure, shape, and dimensionality of MHP NCs. The soft ionic nature of MHP NCs, in conjunction with their low formation energy, rapid anion exchange, and ease of ion migration, enables the rearrangement of their overall appearance via self-assembly or regrowth. Because of their low formation energy and highly dynamic surface ligands, MHP NCs have a higher propensity to regrow than conventional hard-lattice NCs. Moreover, their self-assembly and regrowth can be achieved simultaneously. The self-assembly of NCs into close-packed, long-range-ordered mesostructures provides a platform for modulating their electronic properties (e.g., conductivity and carrier mobility). Moreover, assembled MHP NCs exhibit collective properties (e.g., superfluorescence, renormalized emission, longer phase coherence times, and long exciton diffusion lengths) that can translate into dramatic improvements in device performance. Further regrowth into fused MHP nanostructures with the removal of ligand barriers between NCs could facilitate charge carrier transport, eliminate surface point defects, and enhance stability against moisture, light, and electron-beam irradiation. However, the synthesis strategies, diversity and complexity of structures, and optoelectronic applications that emanate from the self-assembly and regrowth of MHPs have not yet received much attention. Consequently, a comprehensive understanding of the design principles of self-assembled and fused MHP nanostructures will fuel further advances in their optoelectronic applications. In this Account, we review the latest developments in the self-assembly and regrowth of MHP NCs. We begin with a survey of the mechanisms, driving forces, and techniques for controlling MHP NC self-assembly. We then explore the phase transition of fused MHP nanostructures at the atomic level, delving into the mechanisms of facet-directed connections and the kinetics of their shape-modulation behavior, which have been elucidated with the aid of high-resolution transmission electron microscopy (HRTEM) and first-principles density functional theory calculations of surface energies. We further outline the applications of assembled and fused nanostructures. Finally, we conclude with a perspective on current challenges and future directions in the field of MHP.
    • Bimetallic Cu(I)/Rh(II) Relay Catalysis for Multicomponent Polymerization through Carbene Intermediates

      Wang, Ying; Zhu, Linlin; Chen, Wenhao; Zhou, Zhi; Zhang, Zhen; Hadjichristidis, Nikos (Macromolecules, American Chemical Society (ACS), 2022-01-05) [Article]
      A highly efficient and multicomponent step-growth polymerization via carbene intermediates is established by bimetallic relay catalytic systems. This strategy, which provides a facile synthetic pathway to novel luminescent polysulfonamides, could overcome the limitation on the choice of carbene monomers and their difficulty in achieving high-molecular-weight polymers. The polymerizations occur through a tandem Cu(I)-catalyzed click reaction and an Rh(II)-catalyzed carbene 1,3-insertion reaction. The high reactivity of Rh(II)-bonded imino carbene intermediates allows a wide range of reactivity with various carboxylic acids, alcohols, and phenols. These results point to an untapped pathway for the use of metal carbene intermediates to construct new macromolecules.
    • Organic Acid Etching Strategy for Dendrite Suppression in Aqueous Zinc-Ion Batteries

      Wang, Wenxi; Huang, Gang; Wang, Yizhou; Cao, Zhen; Cavallo, Luigi; Hedhili, Mohamed N.; Alshareef, Husam N. (Advanced Energy Materials, Wiley, 2022-01-05) [Article]
      Aqueous zinc ion batteries (AZIBs) represent a promising technology for grid-scale energy storage due to their innate safety, low cost, and environmental friendliness. However, planar Zn foil intrinsically suffers from limited ion and electron transport pathways, poor wettability, and surface passivation, preventing the homogenous deposition of metallic Zn and poor durability of AZIBs. Herein, a 3D Zn foil with hierarchical porous architecture is developed through a facile non-aqueous organic acid etching strategy. The 3D Zn anode is pore-rich and cavity-rich, leading to significantly enhanced accessibility to aqueous electrolytes. Accordingly, this 3D Zn anode enables preferential plating of Zn in the porous texture with suppressed dendrite growth, as confirmed by ex situ scanning electron microscopy and finite element analysis. The cycle life of the 3D Zn anode is sustained over 930 and 1500 h at 4.0 mA cm−2-2.0 mAh cm−2 and 1.0 mA cm−2-1.0 mAh cm−2, respectively. Furthermore, the assembled 3D Zn and α-MnO2 full batteries demonstrate a prolonged cycle life of 3000 cycles with improved rate performance. The etching strategy using non-aqueous organic acid paves a new way to fabricate 3D metal anodes for Zn and other metal anode batteries.
    • Selective benzylic Csp3–H bond activations mediated by a phosphorus–nitrogen PN3P-nickel complex

      Huang, Kuo-Wei; Yao, Changguang; Zhang, Tonghuan; Goncalves, Theo (Chemical Communications, Royal Society of Chemistry (RSC), 2022) [Article]
      In contrast to the typical Csp2−H activation, a PN3P-Nickel complex chemoselectively cleaved the benzylic Csp3–H bond of toluene in the presence of KHMDS, presumably via an in situ generated potassium benzyl intermediate. Under similar conditions, CO underwent deoxygenation to afford the corresponding nickel cyano complex, and ethylbenzene was dehydrogenated to give styrene and a nickel hydride compound. 2,6-xylyl isocyanide was transformed into an unprecedented indolyl complex, likely by trapping the activated benzyl species with a isocyanide moiety.
    • Hydrodynamic Characteristics of an Internal Recycle Berty Catalytic Reactor in Batch/Continuous or Packed/Fluidized Bed Modes

      Cui, Mengmeng; Kulkarni, Shekhar Rajabhau; Wagner, Stefan; Berger-Karin, Claudia; Nagy, Anton; Castaño, Pedro (ACS Engineering Au, American Chemical Society (ACS), 2021-12-15) [Article]
      Berty-type internal recycle reactors offer great opportunities for screening catalysts and reproducing catalytic reacting conditions in multiple processes, thus approaching industrial reactions while amplifying kinetic information. However, the rational design of these reactors requires a deeper understanding of their governing hydrodynamics and equations so that they can be better utilized in batch or continuous mode or as packed or fluidized beds. In this work, by adopting a slice model to represent a three-dimensional symmetric geometry with porous zone settings for catalyst beds, coupled with a species transport model, multiple reference frame, and SST k–ω turbulence model, we developed a computational fluid dynamic simulation strategy of a commercial Berty reactor manufactured by Integrated Lab Solutions (ILS). We conducted experiments to validate the proposed modeling approach under continuous packed bed operations, through which the hydrodynamic behaviors with packed/fluidized beds under the batch mode were also investigated by studying the influences of the transient injection, bed porosities, and rotation rates. As a result, we reported a set of equations to assess the bed velocity and contact time under different porosities, which simplified the performance improvements while replacing the need to perform complex simulations or conduct costly experiments. On the grounds of these hydrodynamic simulations and under various operating conditions, we discussed the pertinence of these instruments for intrinsic kinetic measurements in the batch/continuous or packed/fluidized bed operational modes.
    • Preferred Orientation of TiN Coatings Enables Stable Zinc Anodes

      Zheng, Jiaxian; Cao, Zhen; Ming, Fangwang; Liang, Hanfeng; Qi, Zhengbing; Liu, Wanqiang; Xia, Chuan; Chen, Cuixue; Cavallo, Luigi; Wang, Zhoucheng; Alshareef, Husam N. (ACS Energy Letters, American Chemical Society (ACS), 2021-12-13) [Article]
      Metallic Zn is considered as an ideal anode while its widespread use in rechargeable aqueous batteries still faces many challenges, mostly associated with the dendritic growth and corrosion of Zn and the side reactions. In this work, we demonstrate that a TiN protective coating layer with the preferential (200) orientation can effectively suppress both the Zn dendritic growth and side reactions; more interestingly, it can regulate the growth pattern of the byproduct (zinc hydroxide sulfate or ZHS) by inducing a lateral growth. As a result, reversible Zn plating/stripping over 2300 h at a practical current density of 1 mA cm–2 is achieved along with a nearly 100% Coulombic efficiency. This work not only establishes TiN (200) coatings as an effective Zn anode protective layer but also provides insights into the role of ZHS byproduct as well as strategies to inhibit side reaction and to regulate the growth pattern of ZHS.
    • A Random Forest Classifier for Protein-Protein Docking Models

      Barradas Bautista, Didier; Cao, Zhen; Vangone, Anna; Oliva, Romina; Cavallo, Luigi (Bioinformatics Advances, Oxford University Press (OUP), 2021-12-10) [Article]
      Herein, we present the results of a machine learning approach we developed to single out correct 3D docking models of protein-protein complexes obtained by popular docking software. To this aim, we generated 3 × 104 docking models for each of the 230 complexes in the protein-protein benchmark, version 5 (BM5), using three different docking programs (HADDOCK, FTDock and ZDOCK), for a cumulative set of ≈ 7 × 106 docking models. Three different machine-learning approaches (Random Forest, Supported Vector Machine and Perceptron) were used to train classifiers with 158 different scoring functions (features). The Random Forest algorithm outperformed the other two algorithms and was selected for further optimization. Using a features selection algorithm, and optimizing the random forest hyperparameters, allowed us to train and validate a random forest classifier, named CoDES (COnservation Driven Expert System). Testing of CoDES on independent datasets, as well as results of its comparative performance with machine-learning methods recently developed in the field for the scoring of docking decoys, confirm its state-of-the-art ability to discriminate correct from incorrect decoys both in terms of global parameters and in terms of decoys ranked at the top positions.
    • Straightforward synthesis of [Cu(NHC)(alkynyl)] and [Cu(NHC)(thiolato)] complexes (NHC = N-heterocyclic carbene).

      Ibni Hashim, Ishfaq; Scattolin, Thomas; Tzouras, Nikolaos V; Bourda, Laurens; Van Hecke, Kristof; Ritacco, Ida; Caporaso, Lucia; Cavallo, Luigi; Nolan, Steven P.; Cazin, Catherine S. J. (Dalton transactions, Royal Society of Chemistry (RSC), 2021-12-09) [Article]
      Synthetic access to monomeric copper-alkynyl and copper-thiolato complexes of the type [(NHC)Cu(R)] (R = alkynyl or thiolato) using a weak base approach is reported. All reported reactions proceed under mild conditions in air and in environmentally acceptable solvents. The novel complexes are fully characterized and single crystal X-ray analyses unambiguously establish the atom connectivity in these mononuclear complexes. The importance of the supporting NHC ligand's steric properties in stabilizing mononuclear complexes is discussed.
    • Diblock dialternating terpolymers by one-step/one-pot highly selective organocatalytic multimonomer polymerization

      Xu, Jiaxi; Wang, Xin; Hadjichristidis, Nikos (Nature Communications, Springer Science and Business Media LLC, 2021-12-08) [Article]
      The synthesis of well-defined block copolymers from a mixture of monomers without additional actions (“one-pot/one-step”) is an ideal and industrially valuable method. In addition, the presence of controlled alternating sequences in one or both blocks increases the structural diversity of polymeric materials, but, at the same time, the synthetic difficulty. Here we show that the “one-pot/one-step” ring-opening terpolymerization of a mixture of three monomers ($\textit{N}$-sulfonyl aziridines; cyclic anhydrides and epoxides), with $\textit{tert}$-butylimino-tris(dimethylamino)phosphorene ($\textit{t}$-BuP$_1$) as a catalyst, results in perfect diblock dialternating terpolymers having a sharp junction between the two blocks, with highly-controllable molecular weights and narrow molecular weight distributions ($\textit{Ð}$ < 1.08). The organocatalyst switches between two distinct polymerization cycles without any external stimulus, showing high monomer selectivity and kinetic control. The proposed mechanism is based on NMR, in-situ FTIR, SEC, MALDI-ToF, reactivity ratios, and kinetics studies.
    • Advances in allylic and benzylic C–H bond functionalization enabled by metallaphotoredox catalysis

      Yue, Huifeng; Zhu, Chen; Huang, Long; Dewanji, Abhishek; Rueping, Magnus (Chemical Communications, Royal Society of Chemistry (RSC), 2021-12-06) [Article]
      Metallaphoto-catalysis has been established as a robust platform for efficient construction of a range of chemical bonds. Moreover, transformation of native functionalities such as C(sp3)–H bonds to produce functional molecules represents one of the most attractive strategies in organic synthesis. Merging two powerful methodologies, metallaphoto-catalyzed benzylic and allylic C(sp3)–H bond functionalizations provide a series of general and mild approaches for diversification of alkylbenzenes and alkenes.
    • Molecular engineering of intrinsically microporous polybenzimidazole for energy-efficient gas separation

      Abdulhamid, Mahmoud A.; Hardian, Rifan; Bhatt, Prashant; Datta, Shuvo Jit; Ramirez, Adrian; Gascon, Jorge; Eddaoudi, Mohamed; Szekely, Gyorgy (Applied Materials Today, Elsevier BV, 2021-12-04) [Article]
      Polybenzimidazole (PBI) is a high-performance polymer that exhibits high thermal and chemical stability. However, it suffers from low porosity and low fractional free volume, which hinder its application as separation material. Herein, we demonstrate the molecular engineering of gas separation materials by manipulating a PBI backbone possessing kinked moieties. PBI was selected as it contains NH groups which increase the affinity towards CO$_2$, increase sorption capacity, and favors CO$_2$ over other gasses. We have designed and synthesized an intrinsically microporous polybenzimidazole (iPBI) featuring a spirobisindane structure. Introducing a kinked moiety in conjunction with crosslinking enhanced the polymer properties, markedly increasing the gas separation performance. In particular, the BET surface area of PBI increased 30-fold by replacing a flat benzene ring with a kinked structure. iPBI displayed a good CO$_2$ uptake of 1.4 mmol g$^{−1}$ at 1 bar and 3.6 mmol g$^{−1}$ at 10 bar. Gas sorption uptake and breakthrough experiments were conducted using mixtures of CO$_2$/CH$_4$ (50%/50%) and CO$_2$/N$_2$ (50%/50%), which revealed the high selectivity of CO$_2$ over both CH$_4$ and N$_2$. The obtained CO$_2$/N$_2$ selectivity is attractive for power plant flue gas application requiring CO$_2$ capturing materials. Energy and process simulations of biogas CO$_2$ removal demonstrated that up to 70% of the capture energy could be saved when iPBI was used rather than the current amine technology (methyl diethanolamine [MDEA]). Similarly, the combination of iPBI and MDEA in a hybrid system exhibited the highest CO$_2$ capture yield (99%), resulting in nearly 50% energy saving. The concept of enhancing the porosity of PBI using kinked moieties provides new scope for designing highly porous polybenzimidazoles for various separation processes.
    • Tailored Pore Size and Microporosity of Covalent Organic Framework (COF) Membranes for Improved Molecular Separation

      Shinde, Digambar; Cao, Li; Liu, Xiaowei; Wonanke, Dinga A.D.; Zhou, Zongyao; Hedhili, Mohamed N.; Addicoat, Matthew; Huang, Kuo-Wei; Lai, Zhiping (Journal of Membrane Science Letters, Elsevier BV, 2021-12) [Article]
      Three highly crystalline truxene-based β-ketoenamine COF membranes (TFP-HETTA, TFP-HBTTA and TFP-HHTTA) are fabricated via a de novo monomer design approach to understand the fundamental correlations between pore structure and molecular separation performance. By introducing bulky alkyl groups into the truxene framework, the pore size of TFP-HETTA, TFP-HBTTA, and TFP-HHTTA are systematically tuned from 1.08 to 0.72 nm. Accordingly, the TFP-HETTA showed good water permeance of 47 L m−2 h−1 bar−1 along with a prominent rejection rate of Reactive Blue (RB, 800 Da) but less than 10% rejection rate of inorganic salts. In contrast, the TFP-HHTTA membrane with pore size of 0.72 nm can reject small dye molecules (SO, 350 Da) and trivalent salts but with a moderate water permeance of 19 L m−2 h−1 bar−1. The pore-flow model rooted from the viscous flow could well fit the observed organic solvent nanofiltration results of all three COF membranes.
    • Molecular characteristics of sulfur compounds in oxidative desulfurization for heavy fuel oil based on APPI FT-ICR MS analysis

      Fan, Jiyuan; Saxena, Saumitra; Xiao, Chengkun; Mei, Jinlin; Wang, Gang; Chen, Aiping; Zhang, Wen; Li, Haidong; Duan, Aijun; Roberts, William L. (Catalysis Today, Elsevier BV, 2021-12) [Article]
      Oxidative desulfurization of model oil and heavy fuel oil (HFO) was investigated under mild conditions using H2O2 as an oxidant and acetonitrile as an extractant. The influence factors in the oxidation and extraction processes were evaluated and optimized. The molecular characteristics of the raw feedstock and the desulfurized oils, and the corresponding extraction phases were systematically analyzed by APPI FT-ICR MS, 1H NMR, etc. The results showed that the desulfurization rate of dibenzothiophene reached 97.7% after 10 min reaction, while the sulfur removal efficiency of HFO was 30.7% under optimized conditions. The structures of sulfur compounds were described in heteroatom type, carbon number distribution vs unsaturation degree. The detected main sulfur-containing compounds are S1, S2, S3, NS, OS, O2S, O2S2, and O4S2. Based on the APPI FT-ICR MS results, it can be found that almost all the S1 species have been transformed into sulfone after the oxidation process. Furthermore, the sulfone of O2S1 and O4S2 species in extraction phases were in double bond equivalent (DBE) range from 9 to 25 and carbon number with ≤ 40. 1H NMR results showed that the α to aromatic CH3 combined naphthenic CH-CH2 group accounted for 73.2% in the extraction phase.
    • Stable near-to-ideal performance of a solution-grown single-crystal perovskite X-ray detector

      Kovalenko, Maksym V.; Sakhatskyi, Kostiantyn; Turedi, Bekir; Matt, Gebhard; Lintangpradipto, Muhammad; Naphade, Rounak; Mohammed, Omar F.; Yakunin, Sergii; Bakr, Osman (Research Square Platform LLC, 2021-12-01) [Preprint]
      Abstract The ideal photodetector is the one able to detect every single incoming photon. In particular, in X-ray medical imaging, the radiation dose for patients can then approach its fundamentally lowest limit set by the Poisson photon statistics. Such near-to-ideal X-ray detection characteristics have been demonstrated with only a few semiconductor materials such as Si1 and CdTe2; however, their industrial deployment in medical diagnostics is still impeded by elaborate and costly fabrication processes. Hybrid metal halide perovskites – newcomer semiconductors -– make for a viable alternative3,4,5 owing to their scalable, inexpensive, robust, and versatile solution growth and recent demonstrations of single gamma-photon counting under high applied bias voltages6,7. The major hurdle with perovskites as mixed electronic-ionic conductors, however, arises from the rapid material's degradation under high electric field8,9,10,11, thus far used in perovskite X-ray detectors12,13. Here we show that both near-to-ideal and long-term stable performance of perovskite X-ray detectors can be attained in the photovoltaic mode of operation at zero-voltage bias, employing thick and uniform methylammonium lead iodide (MAPbI3) single crystal (SC) films (up to 300 µm), solution-grown directly on hole-transporting electrodes. The operational device stability is equivalent to the intrinsic chemical shelf lifetime of MAPbI3, being at least one year in the studied case. Detection efficiency of 88% and noise equivalent dose of 90 pGyair (lower than the dose of a single incident photon) are obtained with 18 keV X-rays, allowing for single-photon counting, as well as low-dose and energy-resolved X-ray imaging. These findings benchmark hybrid perovskites as practically suited materials for developing low-cost commercial detector arrays for X-ray imaging technologies.
    • Nearly 100% energy transfer at the interface of metal-organic frameworks for X-ray imaging scintillators

      Wang, Jian-Xin; Gutierrez Arzaluz, Luis; Wang, Xiaojia; Almalki, Maram M.; Yin, Jun; Czaban-Jozwiak, Justyna; Shekhah, Osama; Zhang, Yuhai; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (Matter, Elsevier BV, 2021-12) [Article]
      In this work, we describe a highly efficient and reabsorption-free X-ray-harvesting system using luminescent metal-organic framework (MOF)-fluorescence chromophore composite films. The ultrafast time-resolved experiments and density functional theory calculations demonstrate that a nearly 100% energy transfer from a luminescent MOF with a high atomic number to an organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Such an unprecedented efficiency of interfacial energy transfer and the direct harnessing of singlet and triplet excitons of the TADF chromophore led to remarkable enhancement of radioluminescence upon X-ray radiation. A low detection limit of 256 nGy/s of the fabricated X-ray imaging scintillator was achieved, about 60 times lower than the MOF and 7 times lower than the organic chromophore counterparts. More importantly, this detection limit is about 22 times lower than the standard dosage for a medical examination, making it an excellent candidate for X-ray radiography.
    • AIE-Based Fluorescent Triblock Copolymer Micelles for Simultaneous Drug Delivery and Intracellular Imaging

      Kulkarni, Bhagyashree; Qutub, Somayah S.; Ladelta, Viko; Khashab, Niveen M.; Hadjichristidis, Nikos (Biomacromolecules, American Chemical Society (ACS), 2021-12-01) [Article]
      Fluorescent drug delivery systems have received increasing attention in cancer therapy because they combine drug delivery and bioimaging into a single platform. For example, polymers with aggregation-induced emission (AIE) fluorophores, such as tetraphenylethylene (TPE), have emerged as an elegant choice for drug delivery/bioimaging applications. In this work, we report one-pot sequential organocatalytic ring-opening polymerization of ε-caprolactone (CL) and ethylene oxide (EO) using TPE-(OH)2 as a difunctional initiator, in the presence of a t-BuP2/TEB Lewis pair (catalyst), in THF at room temperature. Two well-defined triblock copolymers with inverse block sequences, TPE-(PCL-b-PEO)2 and TPE-(PEO-b-PCL)2, were synthesized by altering the sequential addition of CL and EO. The physicochemical properties, including hydrodynamic diameter, morphology, and AIE properties of the synthesized amphiphilic triblock copolymers were investigated in aqueous media. The block copolymer micelles were loaded with anticancer drugs doxorubicin and curcumin to serve as drug delivery vehicles. In vitro studies revealed the accelerated drug release at lower pH (5.5), which mimics the tumor microenvironment, different from the physiological pH (7.4). In vitro cytotoxicity studies demonstrated that the neat block copolymer micelles are biocompatible, while drug-loaded micelles exhibited a significant cytotoxic effect in cancer cells. Cellular uptake, examined by confocal laser scanning microscopy, showed that the block copolymer micelles were rapidly internalized by the cells with simultaneous emission of TPE fluorophore. These results suggest that these triblock copolymers can be utilized for intracellular bioimaging.
    • Noncatalytic Oxidative Coupling of Methane (OCM): Gas-Phase Reactions in a Jet Stirred Reactor (JSR)

      Wang, Haoyi; Shao, Can; Gascon, Jorge; Takanabe, Kazuhiro; Sarathy, Mani (ACS Omega, American Chemical Society (ACS), 2021-11-30) [Article]
      Oxidative coupling of methane (OCM) is a promising technique for converting methane to higher hydrocarbons in a single reactor. Catalytic OCM is known to proceed via both gas-phase and surface chemical reactions. It is essential to first implement an accurate gas-phase model and then to further develop comprehensive homogeneous–heterogeneous OCM reaction networks. In this work, OCM gas-phase kinetics using a jet-stirred reactor are studied in the absence of a catalyst and simulated using a 0-D reactor model. Experiments were conducted in OCM-relevant operating conditions under various temperatures, residence times, and inlet CH4/O2 ratios. Simulations of different gas-phase models related to methane oxidation were implemented and compared against the experimental data. Quantities of interest (QoI) and rate of production analyses on hydrocarbon products were also performed to evaluate the models. The gas-phase models taken from catalytic reaction networks could not adequately describe the experimental gas-phase performances. NUIGMech1.1 was selected as the most comprehensive model to describe the OCM gas-phase kinetics; it is recommended for further use as the gas-phase model for constructing homogeneous–heterogeneous reaction networks.
    • Accessibility in Liquid Media: Cyclodehydration of Hexane-2,5-Diol for the Evaluation of Layered Catalysts

      Zaarour, Moussa; Fayad, Ghinwa; Boullay, Philippe; Clet, Guillaume (Advanced Materials Interfaces, Wiley, 2021-11-28) [Article]
      In order to establish layered materials as heterogeneous catalysts in the liquid phase, acidic layered materials are evaluated here through the conversion of hexane-2,5-diol used as a model reaction. Such polyoxygenate reactant is representative of some of the biomass components and the interactions of the reagent or furan product with the interlayers surface is a key to the understanding of these lamellar materials features. Layered HNbMoO6 catalyst is particularly active and stable for the studied reaction compared to several zeolites and its high activity is obtained without any pre-activation step prior to reaction. The influence of temperature and water content in the reaction mixture are also studied for this catalyst. The importance of intercalation in the reaction process is specifically evaluated using Raman spectroscopy and powder X-ray diffraction. On this layered catalyst, the reaction proceeds after intercalation of diol within the interlayer space followed by subsequent cyclodehydration giving rise to 2,5-dimethyltetrahydrofuran with high selectivity. Comparison with related layered materials such as HNbWO6 or H2W2O7 highlights a distinct behavior both in reactivity and intercalation and emphasizes the role of the accessibility to the active sites.
    • Perovskite-Nanosheet Sensitizer for Highly Efficient Organic X-ray Imaging Scintillator

      Wang, Jian-Xin; Wang, Xiaojia; Yin, Jun; Gutierrez Arzaluz, Luis; He, Tengyue; Chen, Cailing; Han, Yu; Zhang, Yuhai; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2021-11-27) [Article]
      The weak X-ray capture capability of organic scintillators always leads to poor imaging resolution and detection sensitivity. Here, we realize an efficient and reabsorption-free organic scintillator at the interface of perovskite nanosheets using a very efficient energy transfer strategy. Our steady-state and ultrafast time-resolved experiments supported by density functional theory calculations demonstrate that an efficient interfacial energy transfer from the perovskite nanosheet to the organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Interestingly, we found that the direct harnessing of both singlet and triplet excitons of the TADF chromophores also contributed greatly to its remarkably enhanced radioluminescence intensity and X-ray sensitivity. A high X-ray imaging resolution of 135 μm and a low detection limit of 38.7 nGy/s were achieved in the fabricated X-ray imaging scintillator.