Development of Sinter-Resistant Core鈥揝hell LaMnxFe1鈥?i>xO3@mSiO2 Oxygen Carriers for Chemical Looping Combustion

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• 作者：Zahra Sarshar ; Zhenkun Sun ; Dongyuan Zhao ; Serge Kaliaguine
• 刊名：Energy & Fuels
• 出版年：2012
• 出版时间：May 17, 2012
• 年：2012
• 卷：26
• 期：5
• 页码：3091-3102
• 全文大小：715K
• 年卷期：v.26,no.5(May 17, 2012)
• ISSN：1520-5029

文摘

This work investigates the possibility of using LaMn_0.7Fe_0.3O_3.15@mSiO₂ as oxygen carriers for chemical looping combustion (CLC). CLC is a new combustion technique with inherent separation of CO₂ from atmospheric N₂. LaMn_0.7Fe_0.3O_3.15@mSiO₂ core鈥搒hell materials were prepared by coating a layer of mesostructured silica around the agglomerated perovskite particles. The oxygen carriers were characterized using different methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ sorption, hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of oxygen (TPD-O₂). The reactivity and stability of the carrier materials were tested in a special reactor, allowing for short contact time between the fluidized carrier and the reactive gas [Chemical Reactor Engineering Centre (CREC) fluidized riser simulator]. Multiple reduction鈥搊xidation cycles were performed. TEM images of the carriers showed that a perfect mesoporous silica layer was formed around samples with 4, 32, and 55 nm in thickness. The oxygen carriers having a core鈥搒hell structure showed higher reactivity and stability during 10 repeated redox cycles compared to the LaMn_0.7Fe_0.3O_3.15 core. This could be due to a protective role of the silica shell against sintering of the particles during repeated cycles under CLC conditions. The agglomeration of the particles, which occurred at high temperatures during CLC cycles, is more controllable in the core鈥搒hell-structured carriers, as confirmed by SEM images. XRD patterns confirmed that the crystal structure of all perovskites remained unchanged after multiple redox cycles. Methane conversion and partial conversion to CO₂ were observed to increase with the contact time between methane and the carrier. Indeed, more oxygen from the carrier surface, grain boundaries, and even from the bulk lattice was released to react with methane. Upon rising the contact time, less CO was formed, which is desirable for CLC application. Increasing the reaction temperature and methane partial pressure lead to enhanced conversions of CH₄ under CLC conditions.