Chemical looping combustion (CLC) is one of the most efficient and advantageous CO2 capture technologies from an economic and energy point of view. An important key factor in this process is the oxygen carriers (OCs) used to transfer oxygen from the air to the fuel. In this work, three natural iron ores from Brazil were selected as interesting oxygen carriers for the CLC process due to their low cost and abundance in nature. Their chemical composition, redox properties, and structural evolution when submitted to a reactivity test in a thermobalance with 15% CH4 and H2 were investigated. The OCs (ItaHP-MG, ItaHP-RN, and ItaLP-RN) revealed good resistance to fracture, and their reactivity increased after the first reaction cycle due to the occurrence of an activation process, leading to a gain in reactivity in the following cycles. The reactivity tests showed that for all OCs, the reactivity with hydrogen was higher when compared to methane, highlighting ItaHP-MG oxygen carrier with relevant rate index values for both fuels (9.60%/min and 3.55%/min for H2 and CH4, respectively). However, OCs performed differently depending on the degree of use of the Fe2O3 phase. Interestingly, ItaHP-MG, with a high Fe2O3 content (96.5%), showed a regeneration of only 60%, while ItaLP-RN, whose Fe2O3 content is 41.5%, presented a degree of use above 85%. This effect is the result of preferential gas–solid interaction on the surface of the OC.

In this work, zinc aluminate spinel powders were prepared by a fast, simple, eco-friendly and low-cost modified Pechini method using commercial gelatin as the organic precursor. The materials were calcinated at 600, 700 and 800 °C and characterized by thermogravimetric analysis, in situ and ex situ X-ray diffraction (XRD), N2-adsorption/desorption isotherms and scanning electron microscopy. The results showed that single phase ZnAl2O4 particles with spinel structure were successfully obtained resulting in a high purity, nanometric, homogeneous and mesoporous materials. The in situ XRD results showed that the crystalline spinel structure of ZnAl2O4 started forming at a temperature lower than 600 °C, revealing powders with crystallite size smaller than 40 nm, which increased with increasing the temperature (91% of increase between 600 and 800 °C). The effect of calcination time showed that the materials calcinated at 600 °C for 3 h presented the higher percentage of crystallite growth due to the increase of crystallinity. The ZnAl2O4 samples retained their pore size up to 700 °C.

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Chemical Looping Combustion (CLC) technology has emerged as a promising alternative capable of restricting the effects of global warming due to anthropogenic gas emissions, especially CO2, through its inherent capture. This study aims to synthesize and evaluate Cu-based oxygen carriers supported on natural materials such as diatomite and kaolin, through the incipient wet impregnation method for CLC process applications. Oxygen carriers were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy with surface energy dispersive x-ray spectroscopy (SEM-EDS). The mechanical strength of the two oxygen carrier particles was determined after the sintering procedure resulting in high crushing force. Reactivity of oxygen carriers was evaluated in a thermobalance with CH4 and H2 gases. Different reaction pathways were attempted when undergoing the redox cycles: total direct reduction of CuO to Cu0 for Cu-K and partial reduction of CuO to Cu2O and CuO to Cu-D. However, the highest reactivity and reaction rate was achieved in Cu-D due to the pore structure of diatomite, the chemical composition and the resulting interaction between CuO and the support. H2 gas reactivity tests showed a higher conversion rate and greater stability between cycles for both oxygen carriers. Thus, the reducible CuO content present in Cu-Diatomite during the reactivity test with H2 as the fuel gas was ideal for achieving high solids conversion, tendency for greater stability and a higher reaction rate.