The amount of CO 2 in the atmosphere is rising due to the combustion of fossil fuels to fulfill the energy demand. The need to build cleaner and more efficient energy systems is motivated by the introduction of chemical looping combustion (CLC) as an alternative to conventional combustion by transferring oxygen. The transfer of oxygen from the air to fuel is carried out by a metal oxide known as an oxygen carrier (OC). For high fuel conversion and oxygen transport capacity, many efforts have been made for the preparation of an OC with minimal material cost. This review aims to summarize the recent advances and development of various types of OCs; particularly those developed within the previous five years are critically discussed in this paper. The main criteria for the selection of the OCs for CLC include their oxygen vacancies, oxygen transport capacities, costs, and tendencies over coke deposition, agglomeration, and attrition. OCs for CLC can be generally divided into single oxides, mixed oxides, natural mineral, spinel from mixed metal oxides, and perovskite. These have been critically discussed with their significance in CLC. The performances, advantages, and limitations of the OCs are presented and compared in detail.

With the recent advancement of the chemical looping combustion (CLC) industry, the development of materials with high stability, high oxidation and reduction rate, and high oxygen transport capacity (OTC) has become a research hotspot. In this paper, the behavior of nickel oxide (NiO) as an oxygen carrier (OC) has been analyzed using thermogravimetric analysis. The influences of the preparation methods and Ni composition have been evaluated to develop Ni-based carriers with high reduction and oxidation rates over 10 redox cycles without changes in the chemical and structural properties. It has been observed that the carriers prepared by the ultrasound irradiation method showed excellent stability and higher reduction and oxidation rate (less than 1–3 min) during multiple redox cycles. However, their OTC values were lower than those of impregnated carriers. It was found that, in the ultrasound irradiation method, the 15NA (15 wt % Ni loading supported with gamma alumina) OC exhibited the highest OTC (3.17%) while 5NA (5 wt % nickel loading supported with gamma alumina) exhibited the lowest OTC (1.34%). A similar trend was observed for the impregnated OC, where 15NA exhibited the highest OTC value (3.67%), whereas 5NA exhibited the lowest OTC value (1.38%). Overall, the carriers prepared via the impregnation method possessed a high value of OTC at approximately 3.67% while the carriers prepared by ultrasound irradiation possessed an OTC value of 3.17%. In terms of physicochemical properties, the carriers prepared using the ultrasound irradiation approach possessed comparatively lower oxidation and reduction temperatures, smaller particle size, higher specific surface area, and more uniform metal distribution on the support. These findings suggested that the Ni-based OC prepared by ultrasound irradiation is a good candidate for CLC reactions.

CO2 levels in the atmosphere are growing as a result of the burning of fossil fuels to meet energy demands. The introduction of chemical looping combustion (CLC) as an alternative to traditional combustion by transporting oxygen emphasizes the need to develop greener and more economical energy systems. Metal oxide, also defined as an oxygen carrier (OC), transports oxygen from the air to the fuel. Several attempts are being made to develop an OC with a reasonable material cost for superior fuel conversion and high oxygen transport capacity (OTC). This study aims to synthesize a potential OC using the wet impregnation method for the CLC process. Thermogravimetric analysis (TGA) was used to determine the cyclic redox properties using 5% CH4/N2 and air as reducing and oxidizing gases, respectively. The 10CuPA-based OC retained a high OTC of about 0.0267 mg O2/mg of OC for 10 cycles that was higher than 10CuA-based OC. Furthermore, the oxygen transfer rate for 10CuPA-based OC was relatively higher compared to 10CuA-based OC over 10 cycles. In comparison to 10CuA-based OC, the 10CuPA-based OC presented a steady X-ray diffraction (XRD) pattern after 10 redox cycles, implying that the phase was stably restored due to praseodymium-modified γ alumina support.

No abstract