Preparation and hydrogen production performance of CaO-Ca₃Al₂O₆@Ni-SiO₂ composite catalyst

Sorption-enhanced steam methane reforming achieves one-step production of high purity hydrogen by in-situ removal of CO₂. However, the volume change of the adsorption component CaO in the composite catalyst during the adsorption and desorption of CO₂ generally caused the structure collapse of the composite catalyst. At the same time, the active component Ni would also be embedded by the generated CaCO₃, resulting in the decline of catalytic and adsorption performance and seriously affecting the purity of hydrogen production. How to prepare bifunctional composite catalyst with high stability is one of the key problems to be solved in the industrial application of this technology. In this work, CaO-Ca₃Al₂O₆@Ni-SiO₂ composite catalyst was prepared by the self-template approach using the cationic surfactant-assisted etching mechanism. In the experiment of hydrogen production by adsorption enhanced CH₄/H₂O reforming, the hydrogen production concentration over the composite catalyst reached 99.6%, and it still remained 97.3% after 10 cycles, which was closely related to the special structure of the prepared CaO-Ca₃Al₂O₆@Ni-SiO₂ composite catalyst. When the reaction was proceeded, the repeated expansion and contraction of CaO-Ca₃Al₂O₆ volume in the composite catalyst was performed in the SiO₂ cavity and would not cause the structure collapse of the composite catalyst. At the same time, the SiO₂ coating on catalytic component Ni could prevent its agglomeration and deactivation during the decarburization and regeneration process. However, it was found that only part of the catalytic component Ni possessed a core-shell structure with Ni as the core and SiO₂ as the shell, and there were some Ni directly loaded on the shell SiO₂, leading to CH₄ conversion dropping from 99.5% to 91.8% in 10 cycles.