Understanding the impact of ash metal components for the characteristics of CaSO4 (010) surface during chemical looping hydrogen production: A first-principles study and thermodynamics analysis

Chemical looping hydrogen production (CLHG) technology is an effective approach for transforming high-carbon energy sources to low-carbon ones while capturing carbon. CaSO4 oxygen carrier is advantageous in CLHG because it is inexpensive and has a high oxygen carrying capacity. When solid fuels, such as coal and sludge, are used, the ash interacts with the oxygen carriers, changing the reduction reaction mechanism. To better understand the micro-nanoscale impacts of ash on oxygen carriers, this research assessed the adsorption and oxygen release capabilities of different ash metal components modified CaSO4 oxygen carriers using a first-principles calculation and real-space functional analysis. According to the thermodynamic calculations, rising temperature lowers adsorption capacity and increases oxygen release capacity. The adsorption capability is as follows: Mg < pristine < Al < Ca < Na < K < Fe, whereas the oxygen release capacity is as follows: Ca < K < Na < Mg < pristine < Fe < Al. All of the adsorption energies of CO on the ash metal components modified CaSO4 surfaces are negative, suggesting that the ash elements can improve CO adsorption capabilities. The interactions between C and modified elements are based on closed-shell interactions, with the degree of interaction defined by their purity. Meanwhile, the correlation of the adsorption energy and information quantities (the absolute value of Shannon entropy and Fisher information) of un-adsorbed surfaces were calculated. The steric hindrance relationship promotes oxygen release, according to the IRI analysis. According to the comprehensive calculation findings of the various ash metal components modified CaSO4 system, Al and Fe have the most influence on enhancing the reduction process for CaSO4 oxygen carrier, with Fe having the highest comprehensive enhancement strength. The results would provide a theoretical basis for regulating the performance of CaSO4 oxygen carrier by ash during the chemical looping hydrogen production system operation.