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1. Phase Stabilized MOCVD Growth of β‐Ga 2 O 3 Using SiO x on c‐Plane Sapphire and AlN/Sapphire Template

   https://doi.org/10.1002/pssa.202300036  

   Jewel, Mohi Uddin ; Hasan, Samiul ; Crittenden, Scott R. ; Avrutin, Vitaliy ; Özgür, Ümit ; Morkoç, Hadis ; Ahmad, Iftikhar ( April 2023 , physica status solidi (a))

   The growth of monoclinic phase‐pure gallium oxide (β‐Ga₂O₃) layers by metal–organic chemical vapor deposition on c‐plane sapphire and aluminum nitride (AlN) templates using silicon‐oxygen bonding (SiO_x) as a phase stabilizer is reported. The β‐Ga₂O₃layers are grown using triethylgallium, oxygen, and silane for gallium, oxygen, and silicon precursors, respectively, at 700 °C, with and without silane flow in the process. The samples grown on sapphire with SiO_xphase stabilization show a notable change from samples without phase stabilization in the roughness and resistivity, from 16.2 to 4.2 nm and from 85.82 to 135.64 Ω cm, respectively. X‐ray diffraction reveals a pure‐monoclinic phase, and Raman spatial mapping exhibits higher tensile strain in the films in the presence of SiO_x. The β‐Ga₂O₃layers grown on an AlN template, using the same processes as for sapphire, show an excellent epitaxial relationship between β‐Ga₂O₃and AlN and have a significant change in β‐Ga₂O₃surface morphology.

    

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2. Micellar Nanoreactors Enabled Site‐Selective Decoration of Pt Nanoparticles Functionalized Mesoporous SiO 2 /WO 3‐x Composites for Improved CO Sensing

   https://doi.org/10.1002/smll.202301011  

   Ma, Junhao ; Xie, Wenhe ; Li, Jichun ; Yang, Haitao ; Wu, Limin ; Zou, Yidong ; Deng, Yonghui ( April 2023 , Small)

   Site‐selective and partial decoration of supported metal nanoparticles (NPs) with transition metal oxides (e.g., FeO_x) can remarkably improve its catalytic performance and maintain the functions of the carrier. However, it is challenging to selectively deposit transition metal oxides on the metal NPs embedded in the mesopores of supporting matrix through conventional deposition method. Herein, a restricted in situ site‐selective modification strategy utilizing poly(ethylene oxide)‐block‐polystyrene (PEO‐b‐PS) micellar nanoreactors is proposed to overcome such an obstacle. The PEO shell of PEO‐b‐PS micelles interacts with the hydrolyzed tungsten salts and silica precursors, while the hydrophobic organoplatinum complex and ferrocene are confined in the hydrophobic PS core. The thermal treatment leads to mesoporous SiO₂/WO_3‐xframework, and meanwhile FeO_xnanolayers are in situ partially deposited on the supported Pt NPs due to the strong metal‐support interaction between FeO_xand Pt. The selective modification of Pt NPs with FeO_xmakes the Pt NPs present an electron‐deficient state, which promotes the mobility of CO and activates the oxidation of CO. Therefore, mesoporous SiO₂/WO_3‐x‐FeO_x/Pt based gas sensors show a high sensitivity (31 ± 2 in 50 ppm of CO), excellent selectivity, and fast response time (3.6 s to 25 ppm) to CO gas at low operating temperature (66 °C, 74% relative humidity).

    

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3. M x La 1–x SiO 2–y N z ( M = Ca/Sr/Ba): Elucidating and Tuning the Structure and Eu 2+ Local Environments to Develop Full-Visible Spectrum Phosphors

   https://doi.org/10.1021/acs.chemmater.2c00252  

   Amachraa, Mahdi ; Li, Shuxing ; Huang, Po-Yuan ; Liu, Ru-Shi ; Wang, Zhenbin ; Xie, Rong-Jun ; Ong, Shyue Ping ( May 2022 , Chemistry of Materials)
4. Resolving the Types and Origin of Active Oxygen Species Present in Supported Mn-Na 2 WO 4 /SiO 2 Catalysts for Oxidative Coupling of Methane

   https://doi.org/10.1021/acscatal.1c02315  

   Sourav, Sagar ; Wang, Yixiao ; Kiani, Daniyal ; Baltrusaitis, Jonas ; Fushimi, Rebecca R. ; Wachs, Israel E. ( August 2021 , ACS Catalysis)

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5. 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/ange.202108201  

   Sourav, Sagar ; Wang, Yixiao ; Kiani, Daniyal ; Baltrusaitis, Jonas ; Fushimi, Rebecca R. ; Wachs, Israel E. ( August 2021 , Angewandte Chemie)

   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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