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1. σ or π? Bonding interactions in a series of rhenium metallotetrylenes

   https://doi.org/10.1039/D1DT00129A  

   Ouellette, Erik T.; Carpentier, Ambre; Joseph Brackbill, I.; Lohrey, Trevor D.; Douair, Iskander; Maron, Laurent; Bergman, Robert G.; Arnold, John (February 2021, Dalton Transactions)

   null (Ed.)

   Salt metathesis reactions between a low-valent rhenium( i ) complex, Na[Re(η 5 -Cp)(BDI)] (BDI = N , N ′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and a series of amidinate-supported tetrylenes of the form ECl[PhC(N t Bu) 2 ] (E = Si, Ge, Sn) led to rhenium metallotetrylenes Re(E[PhC(N t Bu) 2 ])(η 5 -Cp)(BDI) (E = Si ( 1a ), Ge ( 2 ), Sn ( 4 )) with varying extents of Re–E multiple bonding. Whereas the rhenium–stannylene 4 adopts a σ-metallotetrylene arrangement featuring a Re–E single bond, the rhenium–silylene ( 1a ) and –germylene ( 2 ) both engage in π-interactions to form short Re–E multiple bonds. Temperature was found to play a crucial role in reactions between Na[Re(η 5 -Cp)(BDI)] and SiCl[PhC(N t Bu) 2 ], as manipulation of reaction conditions led to isolation of an unusual rhenium–silane, (BDI)Re(μ-η 5 :η 1 -C 5 H 4 )(SiH[PhC(N t Bu) 2 ]) ( 1b ) and a dinitrogen bridged rhenium–silylene, (η 5 -Cp)(BDI)Re(μ-N 2 )Si[PhC(N t Bu) 2 ] ( 1c ), in addition to 1a . Finally, the reaction of Na[Re(η 5 -Cp)(BDI)] with GeCl 2 ·dioxane led to a rare μ 2 -tetrelido complex, μ 2 -Ge[Re(η 5 -Cp)(BDI)] 2 ( 3 ). Bonding interactions within these complexes are discussed through the lens of various spectroscopic, structural, and computational investigations. 

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2. Studies of Functional Defects for Fast Na‐Ion Conduction in Na _{3− y} PS _{4− x} Cl _x with a Combined Experimental and Computational Approach

   https://doi.org/10.1002/adfm.201807951  

   Feng, Xuyong; Chien, Po‐Hsiu; Zhu, Zhuoying; Chu, Iek‐Heng; Wang, Pengbo; Immediato‐Scuotto, Marcello; Arabzadeh, Hesam; Ong, Shyue_Ping; Hu, Yan‐Yan (January 2019, Advanced Functional Materials)

   Abstract All‐solid‐state rechargeable sodium (Na)‐ion batteries are promising for inexpensive and high‐energy‐density large‐scale energy storage. In this contribution, new Na solid electrolytes, Na_3−yPS_4−xCl_x, are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x= 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm⁻¹at 25 °C is achieved for Na_3.0PS_3.8Cl_0.2, which is two orders of magnitude higher compared with that of tetragonal Na₃PS₄(t‐Na₃PS₄). The activation energy (E_a) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cl‐doping while maintaining low Na deficiency in enhanced Na‐ion conduction. Solid‐state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer‐exchange NMR method. The functional detects that promote Na ‐ion transport are maximized for further improvement in ionic conductivity. Full‐cell performance is demonstrated using Na/Na_3.0PS_3.8Cl_0.2/Na₃V₂(PO₄)₃with a reversible capacity of ≈100 mAh g^‐1at room temperature. 

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3. New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na ₂ WO ₄ /SiO ₂ Catalysts

   https://doi.org/10.1002/anie.202108201  

   Sourav, Sagar; Wang, Yixiao; Kiani, Daniyal; Baltrusaitis, Jonas; Fushimi, Rebecca_R; Wachs, Israel_E (August 2021, Angewandte Chemie International Edition)

   Abstract The complex structure of the catalytic active phase, and surface‐gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na₂WO₄/SiO₂catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H₂‐TPR, TAP and steady‐state kinetics) experiments, that the long speculated crystalline Na₂WO₄active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na‐WO_xsites. Kinetic analysis via temporal analysis of products (TAP) and steady‐state OCM reaction studies demonstrate that (i) surface Na‐WO_xsites are responsible for selectively activating CH₄to C₂H_xand over‐oxidizing CH_yto CO and (ii) molten Na₂WO₄phase is mainly responsible for over‐oxidation of CH₄to CO₂and also assists in oxidative dehydrogenation of C₂H₆to C₂H₄. These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na₂WO₄/SiO₂catalysts. 

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4. A combined computational and experimental study of methane activation during oxidative coupling of methane (OCM) by surface metal oxide catalysts

   https://doi.org/10.1039/D1SC02174E  

   Kiani, Daniyal; Sourav, Sagar; Wachs, Israel E.; Baltrusaitis, Jonas (November 2021, Chemical Science)

   The experimentally validated computational models developed herein, for the first time, show that Mn-promotion does not enhance the activity of the surface Na 2 WO 4 catalytic active sites for CH 4 heterolytic dissociation during OCM. Contrary to previous understanding, it is demonstrated that Mn-promotion poisons the surface WO 4 catalytic active sites resulting in surface WO 5 sites with retarded kinetics for C–H scission. On the other hand, dimeric Mn 2 O 5 surface sites, identified and studied via ab initio molecular dynamics and thermodynamics, were found to be more efficient in activating CH 4 than the poisoned surface WO 5 sites or the original WO 4 sites. However, the surface reaction intermediates formed from CH 4 activation over the Mn 2 O 5 surface sites are more stable than those formed over the Na 2 WO 4 surface sites. The higher stability of the surface intermediates makes their desorption unfavorable, increasing the likelihood of over-oxidation to CO x , in agreement with the experimental findings in the literature on Mn-promoted catalysts. Consequently, the Mn-promoter does not appear to have an essential positive role in synergistically tuning the structure of the Na 2 WO 4 surface sites towards CH 4 activation but can yield MnO x surface sites that activate CH 4 faster than Na 2 WO 4 surface sites, but unselectively. 

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5. Synthesis and molecular structure of model silica-supported tungsten oxide catalysts for oxidative coupling of methane (OCM)

   https://doi.org/10.1039/D0CY00289E  

   Kiani, Daniyal; Sourav, Sagar; Wachs, Israel E.; Baltrusaitis, Jonas (May 2020, Catalysis Science & Technology)

   The molecular and electronic structures and chemical properties of the active sites on the surface of supported Na 2 WO 4 /SiO 2 catalysts used for oxidative coupling of methane (OCM) are poorly understood. Model SiO 2 -supported, Na-promoted tungsten oxide catalysts (Na–WO x /SiO 2 ) were systematically prepared using various Na- and W-precursors using carefully controlled Na/W molar ratios and examined with in situ Raman, UV-vis DR, CO 2 -TPD-DRIFT and NH 3 -TPD-DRIFT spectroscopies. The traditionally-prepared catalysts corresponding to 5% Na 2 WO 4 nominal loading, with Na/W molar ratio of 2, were synthesized from the aqueous Na 2 WO 4 ·2H 2 O precursor. After calcination at 800 °C, the initially amorphous SiO 2 support crystallized to the cristobalite phase and the supported sodium tungstate phase consisted of both crystalline Na 2 WO 4 nanoparticles (Na/W = 2) and dispersed phase Na–WO 4 surface sites (Na/W < 2). On the other hand, the catalysts prepared via a modified impregnation method using individual precursors of NaOH + AMT, such that the Na/W molar ratio remained well below 2, resulted in: (i) SiO 2 remaining amorphous (ii) only dispersed phase Na–WO 4 surface sites. The dispersed Na–WO 4 surface sites were isolated, more geometrically distorted, less basic in nature, and more reducible than the crystalline Na 2 WO 4 nanoparticles. The CH 4 + O 2 -TPSR results reveal that the isolated, dispersed phase Na–WO 4 surface sites were significantly more C 2 selective, but slightly less active than the traditionally-prepared catalysts that contain crystalline Na 2 WO 4 nanoparticles (Na/W = 2). These findings demonstrate that the isolated, dispersed phase Na–WO 4 sites on the SiO 2 support surface are the selective-active sites for the OCM reaction. 

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