Cerium Oxide Promoted Iron-based Oxygen Carrier for Chemical Looping Combustion

Abstract

Oxygen carrier (OC) development is an important topic in chemical looping combustion (CLC). Bimetal oxide OCs usually impart better performance than monometal oxide OCs; one example of which is the introduction of CeO2 as a partially reducible material capable of generating oxygen vacancies that lead to faster oxygen transfer inside OC particle. In this study, CeO2 was used as an additive to a Fe2O3-based OC and its effect on physical properties, such as morphology, surface area and crushing strength, was analyzed in detail. The reactivity of OCs during reduction and oxidation was studied using thermogravimetric analysis mass spectrometry and a bench scale CLC setup. The results showed that the reduction reaction at the OC surface was independent of whether CeO2 was present or not, but after the surface oxygen had been consumed during the oxidation of fuel, the OC with CeO2 additive provided faster oxygen transfer rates from the bulk to the surface to produce better average reaction rates. The OCs after reduction and oxidation cycles were characterized by using X-ray diffraction and Raman scattering techniques. The promotional role of the CeO2 additive is postulated that it enables the creation of oxygen vacancies in a solid solution. These vacancies were able to transfer oxygen from Fe2O3 quickly to the surface of the OC by vacancy diffusion or even through an oxygen tunnel formed by vacancies. The formation of a CeO2 and Fe2O3 solid solution provides the prerequisite for these short-range interactions.

Deactivation mechanism of activated carbon supported copper oxide SCR catalysts in C2H4 reductant

“…The SEM imaging was performed on a FEI Quanta 250 embedded with a Bruker Quantax EDS. Raman spectroscopy was accomplished using a Horiba‐Jobin Yvon LabRam HR spectrometer and 442 nm laser excitation to minimize sample fluorescence . The laser was focused on the samples using a confocal microscope having a 50 x objective (Olympus BX‐30‐LWD, NA = 0.5) .…”

La‐hexaaluminate for synthesis gas generation by Chemical Looping Partial Oxidation of Methane Using CO2 as Sole Oxidant

“…After the 2nd cycle by CO 2 oxidation, A values of Fe 3+ (Tr)‐O 5 and Fe 3+ (Th)‐O 4 recovered almost to their original states (42% and 14% vs. 47% and 17% for the fresh sample, Table ), but Fe 3+ (Oh)‐O 6 with the weakest Fe‐O bond strength could not be regenerated corresponding to the absence of the Fe 3+ (Oh)‐O 6 doublet (Figure b). The creation of O 6 ‐Fe 3+ (Oh) vacancy sites might increase the migration rate of oxygen from the bulk to the surface through vacancy diffusion or oxygen tunnels formed by vacancies, which was supported by the enhanced CH 4 reactivity (Figure a) of CO 2 regenerated LF3A. This was quite different from the unselective regeneration of O 2 in which almost all of O 6 ‐Fe 3+ (Oh) (31% vs. 36% for the fresh sample) related to the formation of CO 2 and H 2 O were also recovered due to the high oxidation ability of O 2 .…”

Progress in oxygen carrier development of methane-based chemical-looping reforming: A review

“…The nature of solid OC is always a crucial matter in CLC applications [23]. Since CLC requires OC to be capable to undergo extended cyclic redox reactions with reproducible kinetics at elevated temperatures, materials only showing reactivity above or near their melting points should be eliminated.…”

“…These vacancies are able to transfer oxygen from the bulk of Fe 2 O 3 quickly to the surface of OC through vacancy diffusion or even oxygen tunnels formed by vacancies. Therefore, the formation of Ce-Fe solid solution provides a prerequisite for these short-range interactions [23].…”

“…One of the most important issues in CLC process is the selection of an appropriate OC [22,23]. Typically, OC is composed of a primary metal oxide for active lattice oxygen storage and a ceramic support for enhanced redox stability and activity.…”