1 research outputs found
Development of Sinter-Resistant Core–Shell LaMn<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>O<sub>3</sub>@mSiO<sub>2</sub> Oxygen Carriers for Chemical Looping Combustion
This work investigates the possibility of using LaMn<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3.15</sub>@mSiO<sub>2</sub> as oxygen
carriers for chemical looping combustion (CLC). CLC is a new combustion
technique with inherent separation of CO<sub>2</sub> from atmospheric
N<sub>2</sub>. LaMn<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3.15</sub>@mSiO<sub>2</sub> core–shell 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), N<sub>2</sub> sorption, hydrogen temperature-programmed
reduction (H<sub>2</sub>-TPR), and temperature-programmed desorption
of oxygen (TPD-O<sub>2</sub>). 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–oxidation 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–shell structure showed higher reactivity and
stability during 10 repeated redox cycles compared to the LaMn<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3.15</sub> 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–shell-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 CO<sub>2</sub> 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 CH<sub>4</sub> under CLC conditions