Interaction of Iron Oxide with Alumina in a Composite Oxygen Carrier during the Production of Hydrogen by Chemical Looping

Abstract

Solid solutions of hematite (α-Fe2O3) and corundum (α-Al2O3) have been synthesized by coprecipitation. The resulting particles have been used as oxygen carriers for the production of hydrogen by chemical looping and characterized using X-ray diffraction (XRD), temperature programmed reduction (TPR), specific surface area measurements (BET), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDXS). The particles were repeatedly (i) reduced with, e.g., CO to, nominally, Fe, (ii) then oxidized with steam to Fe3O4 to produce hydrogen, (iii) then returned to Fe2O3 by oxidizing with air. The optimum loading of Al2O3 in the composite particles was found to be 25 wt % for the production of hydrogen over 50 cycles, resulting in an average yield (mole H2 formed/theoretical amount possible on reduction to Fe and oxidation to Fe3O4) of hydrogen of ∼48%. It was found that although Al2O3 is often thought of as inert, it participates in the oxidation and reduction reactions by forming FeAl2O4 and various solid solutions with the iron oxides. This behavior has been explained with the help of phase diagrams, and the applicability of these particles for the production of hydrogen by chemical looping is discussed.

Phase distribution and stepwise kinetics of iron oxides reduction during chemical looping hydrogen generation in a packed bed reactor

“…It is thermodynamically supported to generate FeAl 2 O 4 when Al 2 O 3 was involved in the reaction [42,43]. FeAl 2 O 4 was a little difficult to further reduce to Fe and Al 2 O 3 due to the relatively slow reaction rate [44,45]. The impact of FeAl 2 O 4 on system efficiency needs to be confirmed in future work.…”

Effect of hot pressing temperature on microstructure, mechanical properties and grinding performance of vitrified-metal bond diamond wheels

“…When sintered at 850°C, some weak diffraction peaks of FeAl 2 O 4 appeared. When the hot pressing temperature increased to 900°C, the intensity of FeAl 2 O 4 diffraction peaks slightly increased, which indicated that the crystalline degree of FeAl 2 O 4 obviously improved [10,12].…”

Co3O4 nanoparticles as oxygen carriers for chemical looping combustion: A materials characterization approach to understanding oxygen carrier performance

“…Several transition metal oxides (e.g., those of copper, cobalt, iron, manganese, and nickel) have all been identified as promising oxygen carrier candidates due to their tendency to be easily reduced [4,5]. Fe 2 O 3 and CuO are among the most-investigated materials due to their low cost, but each has drawbacks that may limit their practical implementation at scale (e.g., low oxygen transport capacity of Fe 2 O 3 [6] and adverse environmental implications for CuO) [7]. Despite its higher cost, NiO is also considered a good oxygen carrier due to its high oxygen content and reactivity.…”