Selective Methane Oxybromination over Nanostructured\nCeria Catalysts

Abstract

This\narticle studies the impact of the carrier type (MgO, SiO₂, SiC, Al₂O₃, and ZrO₂) and\nsynthesis method (dry impregnation, coprecipitation, hydrothermal\nsynthesis, and mechanochemical synthesis) on the structure, redox\nproperties, and performance of supported CeO₂ catalysts\nfor methane oxybromination. Major distinctions are evidenced in the\nproduct distribution with respect to bulk CeO₂, and the\nselectivity to methyl bromide (CH₃Br) varies in the following\norder: CeO₂/MgO (61–81%) > CeO₂/SiC\n(56–73%)\n≈ CeO₂/SiO₂ (52–71%) > bulk\nCeO₂ (40%) ≈ CeO₂/ZrO₂ >\nCeO₂/Al₂O₃ (28–35%) at 6–40%\nmethane conversion. The selectivity is primarily governed by the catalyst\npropensity to combust CH₃Br and byproduct dibromomethane\n(CH₂Br₂), which is strongly affected by the\nchoice of the carrier. Specifically, the formation of carbon oxides\nis substantially suppressed over CeO₂ nanoparticles stabilized\non basic MgO (CO_<i>x</i> selectivity <10%)\nwith respect to bulk CeO₂ (CO_<i>x</i> selectivity ≥50%), whereas it is promoted by near atomic\ndispersions of CeO₂ on acidic ZrO₂ and Al₂O₃ carriers. Changes in the size and shape of CeO₂ nanoparticles on MgO had little impact on the selectivity,\nas they exhibit similar oxidation properties after exposure to the\nreaction environment. The synthesis–structure–performance\nrelationships developed demonstrate the great potential of supporting\nCeO₂ to enhance the oxybromination performance.