“…Hollow spheres of metal oxides are intensively investigated for applications, such as controlled release capsules for drugs, fillers, filters [1], gas sensitive materials [1,2], absorbents and separation materials, especially for fixed-bed reactors or chromatography columns [3]. In recent years, hollow spheres of metal oxides have also been intensively investigated for applications as catalysts [3][4][5][6][7]. This is because metal oxide with hollow micro and nanospheres only has low density and good porous structure (usually contain both mesopores and macropores [3]), but also provides a high surface area with more active acid-base oxide centers on the pore surface [4].…”