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1. Exsolution of nanoparticles on A-site-deficient lanthanum ferrite perovskites: its effect on co-electrolysis of CO ₂ and H ₂ O

   https://doi.org/10.1039/D1TA07389C  

   Kim, Jaesung; Ferree, Matthew; Gunduz, Seval; Millet, Jean-Marc M.; Aouine, Mimoun; Co, Anne C.; Ozkan, Umit S. (February 2022, Journal of Materials Chemistry A)

   La 0.7 Sr 0.2 Ni 0.2 Fe 0.8 O 3 (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs. Exsolution of nanoparticles by reduction of LSNF at elevated temperatures can modulate the characteristics of adsorption, electron transfer, and oxidation states of catalytically active atoms, consequently improving the electrocatalytic activity. The exsolution of NiFe and La 2 NiO 4 nanoparticles to the surface of LSNF under reducing atmosphere (5% H 2 /N 2 ) was verified at various temperatures (500–800 °C) by IFFT from ETEM, TPR and in situ XRD. The exsolved nanoparticles obtained uniform size distribution (4.2–9.2 nm) and dispersion (1.31 to 0.61 × 10 4 particle per μm 2 ) depending on the reduction temperature (700–800 °C) and time (0–10 h). The reoxidation of the reduced LSNF (Red-LSNF) was verified by the XRD patterns, indicative of its redox ability, which allows for redistribution of the nanoparticles between the surface and the bulk. TPD-DRIFTS analysis demonstrated that Red-LSNF had superior H 2 O and CO 2 adsorption behavior as compared to unreduced LSNF, which we attributed to the abundance of oxygen vacancy sites and the exsolved NiFe and La 2 NiO 4 nanoparticles. After the reduction of LSNF, the decreases in the oxidation states of the catalytically active ions, Fe and Ni, were characterized on the surface by XPS as well as in the bulk by XANES. The electrochemical performance of the Red-LSNF cell was superior to that of the LSNF cell for electrolysis of H 2 O, CO 2 , and H 2 O/CO 2 . 

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2. “Soft” oxidative coupling of methane to ethylene: Mechanistic insights from combined experiment and theory

   https://doi.org/10.1073/pnas.2012666118  

   Liu, Shanfu; Udyavara, Sagar; Zhang, Chi; Peter, Matthias; Lohr, Tracy L.; Dravid, Vinayak P.; Neurock, Matthew; Marks, Tobin J. (June 2021, Proceedings of the National Academy of Sciences)

   The oxidative coupling of methane to ethylene using gaseous disulfur (2CH 4 + S 2 → C 2 H 4 + 2H 2 S) as an oxidant (SOCM) proceeds with promising selectivity. Here, we report detailed experimental and theoretical studies that examine the mechanism for the conversion of CH 4 to C 2 H 4 over an Fe 3 O 4 -derived FeS 2 catalyst achieving a promising ethylene selectivity of 33%. We compare and contrast these results with those for the highly exothermic oxidative coupling of methane (OCM) using O 2 (2CH 4 + O 2 → C 2 H 4 + 2H 2 O). SOCM kinetic/mechanistic analysis, along with density functional theory results, indicate that ethylene is produced as a primary product of methane activation, proceeding predominantly via CH 2 coupling over dimeric S–S moieties that bridge Fe surface sites, and to a lesser degree, on heavily sulfided mononuclear sites. In contrast to and unlike OCM, the overoxidized CS 2 by-product forms predominantly via CH 4 oxidation, rather than from C 2 products, through a series of C–H activation and S-addition steps at adsorbed sulfur sites on the FeS 2 surface. The experimental rates for methane conversion are first order in both CH 4 and S 2 , consistent with the involvement of two S sites in the rate-determining methane C–H activation step, with a CD 4 /CH 4 kinetic isotope effect of 1.78. The experimental apparent activation energy for methane conversion is 66 ± 8 kJ/mol, significantly lower than for CH 4 oxidative coupling with O 2 . The computed methane activation barrier, rate orders, and kinetic isotope values are consistent with experiment. All evidence indicates that SOCM proceeds via a very different pathway than that of OCM. 

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3. Decoration of Ag nanoparticles on CoMoO4 rods for efficient electrochemical reduction of CO2

   https://doi.org/10.1038/s41598-024-51680-w  

   Ray, Schindra Kumar; Dahal, Rabin; Ashie, Moses D; Bastakoti, Bishnu Prasad (December 2024, Scientific Reports)

   Marszalek, R (Ed.)

   Hydrothermal and photoreduction/deposition methods were used to fabricate Ag nanoparticles (NPs) decorated CoMoO₄rods. Improvement of charge transfer and transportation of ions by making heterostructure was proved by cyclic voltammetry and electrochemical impedance spectroscopy measurements. Linear sweep voltammetry results revealed a fivefold enhancement of current density by fabricating heterostructure. The lowest Tafel slope (112 mV/dec) for heterostructure compared with CoMoO₄(273 mV/dec) suggested the improvement of electrocatalytic performance. The electrochemical CO₂reduction reaction was performed on an H-type cell. The CoMoO₄electrocatalyst possessed the Faraday efficiencies (FEs) of CO and CH₄up to 56.80% and 19.80%, respectively at  − 1.3 V versus RHE. In addition, Ag NPs decorated CoMoO₄electrocatalyst showed FEs for CO, CH₄, and C₂H₆were 35.30%, 11.40%, and 44.20%, respectively, at the same potential. It is found that CO₂reduction products shifted from CO/CH₄to C₂H₆when the Ag NPs deposited on the CoMoO₄electrocatalyst. In addition, it demonstrated excellent electrocatalytic stability after a prolonged 25 h amperometric test at  − 1.3 V versus RHE. It can be attributed to a synergistic effect between the Ag NPs and CoMoO₄rods. This study highlights the cooperation between Ag NPs on CoMoO₄components and provides new insight into the design of heterostructure as an efficient, stable catalyst towards electrocatalytic reduction of CO₂to CO, CH₄, and C₂H₆products. 

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4. Exsolution of nanoparticles on A-site-deficient lanthanum ferrite perovskites: its effect on co-electrolysis of CO2 and H2O

   https://doi.org/DOI https://doi.org/10.1039/D1TA07389C  

   Kim, J; Ferree, M; Gunduz, S; Millet, JMM; Aouine, M; Co, AC; Ozkan, US (November 2021, Journal of materials chemistry)

   La0.7Sr0.2Ni0.2Fe0.8O3 (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs. Exsolution of nanoparticles by reduction of LSNF at elevated temperatures can modulate the characteristics of adsorption, electron transfer, and oxidation states of catalytically active atoms, consequently improving the electrocatalytic activity. The exsolution of NiFe and La2NiO4 nanoparticles to the surface of LSNF under reducing atmosphere (5% H2/N2) was verified at various temperatures (500–800 °C) by IFFT from ETEM, TPR and in situ XRD. The exsolved nanoparticles obtained uniform size distribution (4.2–9.2 nm) and dispersion (1.31 to 0.61 × 104 particle per μm2) depending on the reduction temperature (700–800 °C) and time (0–10 h). The reoxidation of the reduced LSNF (Red-LSNF) was verified by the XRD patterns, indicative of its redox ability, which allows for redistribution of the nanoparticles between the surface and the bulk. TPD-DRIFTS analysis demonstrated that Red-LSNF had superior H2O and CO2 adsorption behavior as compared to unreduced LSNF, which we attributed to the abundance of oxygen vacancy sites and the exsolved NiFe and La2NiO4 nanoparticles. After the reduction of LSNF, the decreases in the oxidation states of the catalytically active ions, Fe and Ni, were characterized on the surface by XPS as well as in the bulk by XANES. The electrochemical performance of the Red-LSNF cell was superior to that of the LSNF cell for electrolysis of H2O, CO2, and H2O/CO2. 

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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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