Particulate Formation from a Copper Oxide-Based Oxygen Carrier in Chemical Looping Combustion for CO2 Capture

Tuning the Support Properties toward Higher CO2 Conversion during a Chemical Looping Scheme

The chemical looping process is promising for CO₂ conversion because of the much higher CO₂ conversion efficiency than the photocatalytic and electrocatalytic processes. Conventional oxygen carriers have to include a high content of inert support, typically Al₂O₃, to avoid sintering, thus leading to a trade-off between reactivity and stability. Here, we propose the use of ion-conductive Gd_xCe_2-xO_2-δ (GDC) to prepare the supported oxygen carriers. The resulting Fe₂O₃/GDC materials achieve both high reactivity and stability. Fe₂O₃/Gd_0.3Ce_1.7O_2-δ shows high CO productivity (∼10.79 mmol·g^-1) and CO production rate (∼0.77 mmol·g^-1·min^-1), which are twofold higher than that of Fe₂O₃/Al₂O₃. The performance remains stable even after 30 cycles. The mechanism study confirmed the rate-limiting role of the oxygen-ion conductivity, and the GDC support enhanced the oxygen-ion conductivity of oxygen carriers during the redox reactions, thus leading to improved CO₂ splitting performance. A roughly linear relationship between the oxygen-ion conductivity and CO₂ yield is also obtained and verified in our testing conditions. This relation can be used to predict and select oxygen carriers with high CO₂ splitting performance.

Autothermal CaO Looping Biomass Gasification for Renewable Syngas Production

Biomass gasification is regarded as a promising alternative to fossil fuels for producing sustainable and clean value-added products. However, the challenges including low energy efficiency, CO₂ emission, and ash agglomeration significantly delay the deployment of the technology. Herein, we first proposed a novel autothermal CaO looping biomass gasification (Auto-CaL-Gas) technology, in which CaO-based materials react with flue gas with a high concentration of CO₂ (>30 vol %) to produce heat inside the gasifier, simultaneously providing energy for low-temperature biomass gasification using CO₂ as a gasification agent. Upon use of this concept the syngas production exhibited a significant increase from 0.21 kg/h to 0.90 kg/h in the Aspen simulation results and more than 3-fold improvement in the experimental results.

Inert chemical looping conversion of biochar with iron ore as oxygen carrier: Products conversion kinetics and structural evolution

In this study, biochar obtained from pyrolysis of woody shavings at 550 °C was reacted with iron ore in N₂ to investigate its inert chemical looping conversion properties, including the gas products conversion kinetics and structural evolution process. Results found that both the release of CO and CO₂ could be divided into rapid release stage and stable chemical looping reaction stage with activation energies of 17.69 and 45.65 kJ/mol, respectively. During the chemical looping process, the reaction reactivity of biochar reduced gradually with the amorphous char structure turning into fused ring structure and finally into graphite crystal structure. Simultaneously, Fe₂O₃ was reduced into Fe₃O₄, FeO and Fe. This work highlighted the chemical conversion of biochar using natural iron ore as oxygen carrier in inert N₂ atmosphere from the common in-situ gasification chemical looping process using CO₂/H₂O as agent.