Component synergy and armor protection induced superior catalytic activity and stability of ultrathin Co-Fe spinel nanosheets confined in mesoporous silica shells for ammonia decomposition reaction

[Display omitted] •Ultrathin Co-Fe spinel oxide nanosheets with adjustable stoichiometry confined in mesoporous SiO2 shell.•Ammonia decomposition reaction of encapsulating CoxFe3-xO4 nanosheets with mSiO2 shells was studied.•The mesoporous SiO2 shell effectively prevent the coalescence of CoxFe3-xO4 nanosheets during catalytic process.•The tunable stoichiometry of CoxFe3-xO4 regulates the electron structure and optimizes the nitrogen desorption ability.•The strong synergistic coupling effect between CoxFe3-xO4 and mSiO2 may account for excellent performance. We report the fabrication of ultrathin Co-Fe spinel oxide nanosheets with adjustable stoichiometry confined in mesoporous SiO2 shells (CoxFe3-xO4@mSiO2) by encapsulating Fe-Co layered double hydroxides (FeCo-LDHs) with mesoporous SiO2 shells followed with a calcination process. In this way, the unique 2D structured CoxFe3-xO4@mSiO2 nanosheets offers high specific surface area and intimate contact with NH3. The tunable stoichiometry of CoxFe3-xO4 nanosheets regulate the electron structure and thus optimize the nitrogen desorption ability. The encapsulation of mSiO2 shells not only effectively facilitates the generation of ultrathin Co-Fe spinel oxides nanosheets with abundant active sites, but also protects CoxFe3-xO4 nanosheets from detachment and agglomeration during the NH3 decomposition reaction. Benefiting from these advantages, the optimal Co0.89Fe2.11O4@mSiO2 nanosheet catalyst possesses 88% conversion of ammonia at 600 °C with a space velocity of 60 000 cm3 g−1 h−1 and maintains even 48 h without attenuation.