Mesoporous Co₃O₄ with Controlled Porosity: Inverse Micelle Synthesis and High-Performance Catalytic CO Oxidation at −60 °C

Abstract

Crystalline mesoporous cobalt oxides with improved catalytic activity in CO oxidation were synthesized using an inverse surfactant micelle method. The prepared materials are monodispersed nanoparticle aggregates, and the mesopores are formed by connected intraparticle voids. Powder X-ray diffraction (PXRD), N 2 sorption, field emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed that both pore and nanoparticle sizes are enlarged with increasing thermal treatment temperatures (150–450 °C). Mesoporous cobalt oxide calcined at 350 °C exhibited the best oxidation activity and can achieve complete oxidization (100% conversion) of CO to CO 2 at −60 °C under normal conditions (∼3–10 ppm of H 2 O) and at 80 °C under moisture rich conditions (∼3% H 2 O). The commercial Co 3 O 4 reached 100% conversion at 220 °C under normal conditions. X-ray photoelectron spectroscopy (XPS), O 2 -temperature-programmed desorption (O 2 -TPD), H 2 -temperature-programmed reduction (H 2 -TPR), CO-TPD, and N 2 sorption analyses indicated that the surface oxygen vacancy and large surface area promoted the lattice oxygen mobility of the catalysts and further enhanced their catalytic performance. The catalysts were deactivated by accumulation of water and formation of carbonates, but their activities can be easily restored by expelling water and carbonates at moderate temperature (200 °C).