Porous hollow manganites with robust composite shells for oxidation of CO at low temperatureElectronic supplementary information (ESI) available. See DOI: 10.1039/c6ra20868a

Yolk- and hollow-type manganite-coated silica (SiO 2 ) microspheres were synthesized via the thermal hydrolysis of urea using a dissolution and deposition method. Core/shell SiO 2 microspheres were used as templates; the products were then annealed at 700 °C for 10 h under an O 2 atmosphere. Yolk microspheres (Mn 2 O 3 /SiO 2 _1T and Mn 2 O 3 /SiO 2 _2T) were obtained when the dissolution and deposition step was repeated once and twice, respectively, while hollow microspheres (Mn 2 O 3 /SiO 2 _3T) were produced when the method was repeated three times. The microspheres had average diameters of 300-310 nm. The Mn 2 O 3 /SiO 2 _3T product possessed the largest Brunauer-Emmett-Teller (BET) surface area and exhibited the best catalytic performance with regard to CO oxidation. The complete conversion of CO was achieved at approximately 200 °C. Other microspheres, including Mn 3 O 4 /SiO 2 _3T, NiO/SiO 2 _3T, and Ni/SiO 2 _3T, yielded much lower activities than the Mn 2 O 3 /SiO 2 _3T catalyst. The large surface area of the Mn 2 O 3 /SiO 2 _3T microsphere sample, as well as the presence of Mn 3+ ions, appears to be responsible for its superior catalytic CO oxidation activity amongst the tested catalysts. Hollow-type manganite-coated silica microspheres were synthesized via the thermal hydrolysis of urea. The Mn 2 O 3 /SiO 2 _3T microspheres with robust shells exhibit best catalytic performance for CO oxidation even at temperatures below 200 °C.