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

Abstract

Sub-10 nm Co3O4 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 Co3O4 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 Co3O4 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 Co3O4 nanoparticles, respectively. Density functional theory (DFT) calculations and thermogravimetry coupled with mass spectrometry (TG-MS) analysis reveal that the size-dependent catalytic activity of Co3O4 for AP decomposition origin from varied O2 activation ability and NH3 adsorption capacity at the edge and corner sites.