In Search of Factors Determining Activity of Co3O4 Nanoparticles Dispersed in Partially Exfoliated Montmorillonite Structure.

The paper discusses a formation of Mt-PAA composite containing a natural montmorillonite structure partially exfoliated by poly(acrylic acid) introduced through intercalation polymerization of acrylic acid. Mt-PAA was subsequently modified by controlled adsorption of Co2+ ions. The presence of aluminosilicate packets (clay) and carboxyl groups (hydrogel) led to the deposition of significant amounts of Co2+ ions, which after calcination formed the Co3O4 spinel particles. The conditions of the Co2+ ions' deposition (pH, volume and concentration of Co(NO3)2 solution, as well as a type of pH-controlling agent) were widely varied. Physicochemical characterization of the prepared materials (including X-ray fluorescence (XRF), X-ray powder diffraction (XRD), low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H2-TPR)) revealed that the modification conditions strongly influenced the content as well as the distribution of the Co3O4 active phase, tuning its reducibility. The latter parameter was, in turn, very important from the point of view of catalytic activity in the combustion of aromatic volatile organic compounds (VOCs) following the Mars-van Krevelen mechanism.