Catalytic activity of mesoporous cobalt oxides with controlled porosity and crystallite sizes: Evaluation using the reduction of 4-nitrophenol

Mesoporous cobalt oxides were synthesized using an inverse surfactant micelle method. The prepared materials are mono-dispersed nanoparticle aggregates with connected, well defined intra-particle voids. Powder X-ray diffraction, N₂ sorption, scanning electron microscopy and transmission electron microscopy revealed that both pore and nanoparticle sizes are enlarged with thermal treatment temperatures. Nitrogen sorption experiments revealed that the pore diameters increased from 12.1 to 31.9 nm with the final heat treatment increase from 150 to 550 °C. The reduction of 4-nitrophenol has been chosen as a well-controlled model reaction allowing us to determine the catalytic activity as a function of crystallite size and pore diameter. A comparison of the various cobalt oxide catalysts is made in terms of Langmuir-Hinshelwood kinetics.