Surfactant-free synthesis of sub-10 nm Co3O4 in a rotating packed bed and its high catalytic activity for AP pyrolysis.

• Sub-10 nm Co 3 O 4 is synthesized by surfactant-free precipitation in RPB reactor. • The size of Co 3 O 4 nanoparticle is inherited from the thickness of precursory Co(OH) 2. • Sub-10 nm Co 3 O 4 shows the best catalytic performance for AP decomposition. • Size effect of Co 3 O 4 in AP decomposition has been studied experimentally and theoretically. Sub-10 nm Co 3 O 4 nanoparticles with a narrow size distribution are prepared by a surfactant-free liquid precipitation method in a rotating packed bed (RPB) reactor. The mean size of the material is about 8.5 nm, and is the smallest among previous reports via surfactant-free liquid precipitation. The growth mechanisms show that the sizes of Co 3 O 4 nanoparticles inherit from the precursory Co(OH) 2. Compared to the traditional stirred tank reactor, RPB can enhance the nucleation of Co(OH) 2 through enhanced micro-mixing, which leads to thinner and more uniform products. As-prepared Co 3 O 4 can show enhanced catalytic performance for ammonium perchlorate (AP) decomposition. The peak temperatures of AP decomposition reduce to 296.8 °C, 291.8 °C, 290.0 °C, and 286.6 °C by adding 2 wt% 22.6 nm, 15.0 nm, 10.9 nm, and 8.5 nm of Co 3 O 4 nanoparticles, respectively. Density functional theory (DFT) calculations and thermogravimetry coupled with mass spectrometry (TG-MS) analysis reveal that the size-dependent catalytic activity of Co 3 O 4 for AP decomposition origin from varied O 2 activation ability and NH 3 adsorption capacity at the edge and corner sites. [ABSTRACT FROM AUTHOR]