A TEOM-MS study on the interaction of N2O with a hydrotalcite-derived multimetallic mixed oxide catalyst Original Research Article

The interaction of N2O with a multimetallic mixed oxide (ex-Co,Mg-Rh,Al-HTlc), prepared via calcination of a hydrotalcite-like compound, has been studied employing a tapered element oscillating microbalance coupled to a mass spectrometer (TEOM-MS), capable of simultaneous recording of mass and gas-phase composition variations during the process. The study is based on step–response experiments (SRE) carried out at different temperatures, ranging from 303 to 598 K. The observed mass variations are related to the amount of adsorbed species under reaction conditions and their stability. The gas analysis gave simultaneous information on the rate of N2O decomposition and the steady-state condition. Based on the results obtained and literature data, an interaction model of N2O with the mixed oxide, including the exchange of the adsorbed oxygen with the catalyst lattice oxygen, is proposed. At low temperatures (303 K) molecular adsorption of N2O is also considered. The experimental time- and temperature-dependent mass variations can be well described. Oxygen recombination/desorption and oxidation of the surface sites appeared to be the slowest processes, while the removal of adsorbed oxygen by N2O from the gas phase was much faster. Activation energies of the steps involved range between 16 and 40 kJ/mol. The observed mass changes are mainly attributed to the Co in the mixed oxide matrix.