Hydrotalcite-derived cobalt–aluminum mixed oxide catalysts for toluene combustion

Abstract

Hydrotalcite-like compounds (HTlcs) containing cobalt and aluminum (intended Co/Al molar ratio=3.0) were coprecipitated at 30, 50 and 70°C. Their crystallinity, which was confirmed by powder X-ray diffraction, increased with the precipitation temperature. Furthermore, HTlcs with various cobalt contents were prepared at 70°C. Thermogravimetric analysis showed that HTlcs were transformed into stable oxides at 550°C. The decrease in the crystallite size of the formed spinels with the increase in the precipitation temperature was observed. Low temperature sorption of nitrogen revealed meso-macroporous nature of the oxides with extended interparticle porosity. Aluminum segregated on the samples surface, which contained various amounts of lattice and adsorbed/electrophilic oxygen as detected by X-ray electron spectroscopy. The high ratio of lattice to adsorbed/electrophilic oxygen found for the sample with Co/Al=3:1 caused that it turned out to be the most efficient catalyst in the total oxidation of toluene (50% conversion at 257°C).