## 1 Introduction  
Hydrogen as an alternative energy carrier has attracted much attention recently due to its high calorific value and non-polluting combustion, which produces water as a reaction product [1; 2]. About 80-85% of global hydrogen is produced from fossil fuels like natural gas and liquid hydrocarbons through three different processes: steam reforming (SR), partial oxidation (POX), and autothermal reforming (ATR) [3; 4]. These processes can contribute to the increase in annual global carbon emissions. Since carbon dioxide is produced as a by-product, the CO\({}_{2}\) should be captured to ensure a sustainable (zero-emission) process and to prevent its negative economic and environmental impact [5; 6]. The Paris Agreement on climate change emphasizes the crucial need to limit the temperature increase to 1.5 \({}^{\circ}\)C above pre-industrial levels. Hydrogen and its derivatives will contribute 10% of total emissions reduction by 2050. Fossil fuel-based hydrogen production is expected to expand from 0.04 Gt/year of captured CO\({}_{2}\) currently to 3.4 Gt/year of CO\({}_{2}\) in 2050 [7]. In the Paris Agreement 1.5 \({}^{\circ}\)C scenario, green and blue hydrogen production groups from negligible levels to 19 EJ (154 million tonnes) by 2030 and over 74 EJ (614 million tonnes) by 2050 [8]. Accordingly, the produced hydrogen needs to be low carbon (Blue Hydrogen) or zero carbon (Green Hydrogen), which is produced by water electrolysis using renewable electricity [9]. Clean hydrogen would play an important role in the industrial sector, such as steel production, chemicals, and petrochemicals. Clean hydrogen use is projected to grow to 16 EJ by 2030 and over 38 EJ by 2050. Hydrogen can also play a vital role in balancing renewable electricity supply and demand by offering alternative long-term storage and helping control the variability of energy production across seasons. Hydrogenstorage provides long-term seasonal flexibility from 2030 onwards, with an estimated storage capacity of 2000 TWh by 2050 [10]. The choice of suitable CO2 removal sorbents is based on criteria such as capacity, selectivity, adequate adsorption/desorption kinetics, significant stability, low cost, and ease of regeneration [11; 12]. The most commonly used sorbent for SESR is calcium oxide (CaO), which can reversibly react with CO2 to form calcium carbonate. Much attention has been given to CaO due to its high CO2 capture capacity and its low cost [13; 14]. The deactivation of CaO-based sorbent over multiple cycles of carbonation/decarbonation reactions is well known in the literature [12; 13]. It was reported that the CO2 adsorption capacity of natural CaO declines by 80% after a few cycles (10-20 cycles) [15]. CaO sintering and particle agglomeration were suggested to be the main causes of this dramatic drop. Sintering of the sorbents usually occurs at high regeneration temperatures and causes irreversible physical changes, such as the loss of the porous structure [12].  
In the current work, novel synthetic CaO-based sorbents for carbon dioxide (CO2) capture in sorption-enhanced steam reforming (SESR) were prepared by the co-precipitation method. Magnesium oxide (MgO) and cerium oxide (CeO2) were added to calcium oxide (CaO) in different molar percentages to obtain the optimum percentage for achieving high and efficient CO2 uptake capacity and cyclic stability. The prepared samples were structurally characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The thermal behavior and calcination temperature were obtained by thermogravimetric analysis (TGA) and the surface area by N2 adsorption analysis. Finally, the performance of the materials was studied and evaluated by multi-cycle carbonization/decarbonization test.