Combustão catalítica de metano utilizando espinélio de cobalto proveniente de óxidos mistos de Co, Mg e Al obtidos da calcinação de hidróxidos duplos lamelares

Abstract

The demand for electricity production, and the need for thermoelectric use as power generating units, makes it necessary to search for less polluting matrices. In this search the catalytic combustion of methane, both from natural gas and other sources (residue disposal, for example) have shown promising. It is known the use of cobalt oxides is an alternative to the use of catalysts based on noble metals which has shown high performance. In order to potentiate the activity of the cobalt based catalyst, thus reducing both the ignition temperature and the temperature of total burning of methane, this work proposes the production of cobalt-based precursors using different types of layered double hydroxides (LDHs). Cobalt based catalysts partially substituted in layered double hydroxides (LDH Mg, Al and CO32-) were prepared by co-precipitation and impregnation with a nominal content of 9% CoII in LDH, or by impregnating a commercial hydrotalcite (HT). The LDH precursors were characterized by X-ray powder diffraction (XRD) and infrared absorption spectroscopy (FTIR). The XRD patterns indicated a LDH of 3R polytype. XRD showed the presence of Gibbisite in the HT precursor. The infrared spectra of precursor LDHs presented bands related to ν1, ν2 and ν3 vibrations of the carbonate anion, and interlayer water characteristic bands, thus in line with the XRD data. Analysis by XRD of the catalysts after calcination at 800 °C showed the presence of periclase and spinel phases. Infrared spectra showed bands ascribed to the Mg-O and Co-O stretching in tetrahedral and octahedral sites as well as bands attributed to the Mg-O-Al bond and the cobalt spinel. The catalytic activity of these materials was investigated in the catalytic combustion of methane under kinetic regime, using predetermined reaction conditions to avoid diffusional limitations, resulting in a significant decrease in the combustion temperature, with the higher activity observed for the catalyst prepared by impregnating a commercial HT. Scanning electron microscopy (SEM) and quantitative chemical analysis (EDS) of catalysts with improved performance show both the homogeneous dispersion of the components in the sample surface and the higher aluminum content of the sample supported on HT.