Ultrasonic-spray-assisted synthesis of metal oxide hollow/mesoporous microspheres for catalytic CO oxidation

Transition metal oxides with hollow or mesoporous microstructures represent a unique class of heterogeneous catalysts or catalyst supports with many fascinating features such as the large surface areas, tunable pore sizes and volumes, multitude of compositions, and ease of functionalization. In this work, we demonstrated a general ultrasonic-spray-assisted synthesis of various transition metal oxide hollow/mesoporous microspheres, using only low-cost commercial metal chlorides as precursors and water as solvent. As typical examples, five mono-component metal oxides (CeO2, alpha-Fe2O3, Co3O4, SnO2 and TiO2) hollow or mesoporous microspheres were prepared and their formation mechanisms were discussed. The catalytic carbon monoxide (CO) oxidation indicated that these metal oxide products exhibited improved catalytic activities than some of those reported previously, due to their tiny crystalline grains, large pore volume and specific surface area. The universality of this synthetic method was also demonstrated in producing multi-component and multi-functional metal oxides with hollow/mesoporous structures. This work therefore provides an industrial level producing method for the scalable preparation of various metal oxide hollow/mesoporous microspheres which are expected to be used as high-performance catalysts or catalyst supports in more chemical reactions.