“…The successful development of the SESR process relies on the type of the employed catalyst and sorbent, as well as their mixing pattern, i.e., physical mixing or integrating the catalyst and sorbent into a single particle. , Regarding the type of catalyst and sorbent, Ni-based catalysts and CaO-based sorbents have received the most attention due to their high ability to, respectively, break C–C bonds and capture CO 2 , high availability, and low cost. , Concerning the mixing pattern, the CO 2 produced during the SR and WGS reactions needs to diffuse from the interior surface of the catalyst through the catalyst pore structure and the bulk of the fluid to the neighboring sorbent where it can be adsorbed in the case of physical mixing. Nevertheless, the direct on-site sorption of CO 2 can be realized if the catalyst and sorbent are integrated into a single particle, i.e., bifunctional catalyst sorbent. ,− Therefore, since the late 2000s, Ni–CaO-based catalyst-sorbent bifunctional materials have been receiving more and more attention for high-purity hydrogen production via SESRG process. − However, carbon deposition on Ni active sites can not only decrease the catalytic activity of the Ni–CaO-based bifunctional materials but also reduce the access of CO 2 to active CaO sites by blocking the pores and/or adhering to the surface of the sorbent at high temperatures . Embedding Ni in the NiAl 2 O 4 spinel structure, which provides a high distribution of small Ni active sites after reduction, has been well recognized as one of the most efficient approaches to reduce coke formation on metallic Ni. , However, the thermodynamic stability of NiAl 2 O 4 inhibits the diffusion of Ca 2+ into this spinel structure to create a close contact with Ni and Al species.…”